1,956 research outputs found
Influence of Sulfur-Containing Diamino Acid Structure on Covalently Crosslinked Copolypeptide Hydrogels.
Biologically occurring non-canonical di-α-amino acids were converted into new di-N-carboxyanhydride (di-NCA) monomers in reasonable yields with high purity. Five different di-NCAs were separately copolymerized with tert-butyl-l-glutamate NCA to obtain covalently crosslinked copolypeptides capable of forming hydrogels with varying crosslinker density. Comparison of hydrogel properties with residue structure revealed that different di-α-amino acids were not equivalent in crosslink formation. Notably, l-cystine was found to produce significantly weaker hydrogels compared to l-homocystine, l-cystathionine, and l-lanthionine, suggesting that l-cystine may be a sub-optimal choice of di-α-amino acid for preparation of copolypeptide networks. The di-α-amino acid crosslinkers also provided different chemical stability, where disulfide crosslinks were readily degraded by reduction, and thioether crosslinks were stable against reduction. This difference in response may provide a means to fine tune the reduction sensitivity of polypeptide biomaterial networks
On prevarieties of logic
It is proved that every prevariety of algebras is categorically equivalent to
a "prevariety of logic", i.e., to the equivalent algebraic semantics of some
sentential deductive system. This allows us to show that no nontrivial equation
in the language "meet, join, and relational product" holds in the congruence
lattices of all members of every variety of logic, and that being a
(pre)variety of logic is not a categorical property
Molecular confirmation of Sarcocystis fayeri in a donkey
Sarcocystis fayeri is a canine protozoan parasite with an equine intermediate host. Historically classified as an incidental pathogen, recent literature has described the toxic effects of Sarcocystis fayeri in human food poisoning, and highlighted potential involvement in equine neuromuscular disease. Until now, horses were believed to be the exclusive intermediate host. This study reports the first molecular confirmation of S. fayeri in a donkey, and gives rise to the consideration of donkeys being a potential reservoir for the parasite. This finding is of particular importance in understanding the epidemiology of this disease
Epimorphisms in varieties of subidempotent residuated structures
A commutative residuated lattice A is said to be subidempotent if the lower
bounds of its neutral element e are idempotent (in which case they naturally
constitute a Brouwerian algebra A*). It is proved here that epimorphisms are
surjective in a variety K of such algebras A (with or without involution),
provided that each finitely subdirectly irreducible algebra B in K has two
properties: (1) B is generated by lower bounds of e, and (2) the poset of prime
filters of B* has finite depth. Neither (1) nor (2) may be dropped. The proof
adapts to the presence of bounds. The result generalizes some recent findings
of G. Bezhanishvili and the first two authors concerning epimorphisms in
varieties of Brouwerian algebras, Heyting algebras and Sugihara monoids, but
its scope also encompasses a range of interesting varieties of De Morgan
monoids
Bringing Age Back In: Accounting for Population Age Distribution in Forecasting Migration
The link between age and migration propensity is long established, but
existing models of country-level net migration ignore the effect of population
age distribution on past and projected migration rates. We propose a method to
estimate and forecast international net migration rates for the 200 most
populous countries, taking account of changes in population age structure. We
use age-standardized estimates of country-level net migration rates and
in-migration rates over quinquennial periods from 1990 through 2020 to
decompose past net migration rates into in-migration rates and out-migration
rates. We then recalculate historic migration rates on a scale that removes the
influence of the population age distribution. This is done by scaling past and
projected migration rates in terms of a reference population and period. We
show that this can be done very simply, using a quantity we call the migration
age structure index (MASI). We use a Bayesian hierarchical model to generate
joint probabilistic forecasts of total and age- and sex- specific net migration
rates over five-year periods for all countries from 2020 through 2100. We find
that accounting for population age structure in historic and forecast net
migration rates leads to narrower prediction intervals by the end of the
century for most countries. Also, applying a Rogers & Castro-like migration age
schedule to migration outflows reduces uncertainty in population pyramid
forecasts. Finally, accounting for population age structure leads to less
out-migration among countries with rapidly aging populations that are forecast
to contract most rapidly by the end of the century. This leads to less drastic
population declines than are forecast without accounting for population age
structure.Comment: 29 pages, 8 figures, 3 table
Inconsistency lemmas in algebraic logic
In this paper, the inconsistency lemmas of intuitionistic and classical propositional logic are formulated abstractly.
We prove that, when a (finitary) deductive system is algebraized by a variety K, then has an inconsistency
lemma—in the abstract sense—iff every algebra in K has a dually pseudo-complemented join semilattice of
compact congruences. In this case, the following are shown to be equivalent: (1) has a classical inconsistency
lemma; (2) has a greatest compact theory and K is filtral, i.e., semisimple with EDPC; (3) the compact
congruences of any algebra in K form a Boolean lattice; (4) the compact congruences of any A ∈ K constitute
a Boolean sublattice of the full congruence lattice of A. These results extend to quasivarieties and relative
congruences. Except for (2), they extend even to protoalgebraic logics, with deductive filters in the role of
congruences. A protoalgebraic system with a classical inconsistency lemma always has a deduction-detachment
theorem (DDT), while a system with a DDT and a greatest compact theory has an inconsistency lemma. The
converses are false.http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1521-3870hb201
Latent class analysis variable selection
We propose a method for selecting variables in latent class analysis, which is the most common model-based clustering method for discrete data. The method assesses a variable's usefulness for clustering by comparing two models, given the clustering variables already selected. In one model the variable contributes information about cluster allocation beyond that contained in the already selected variables, and in the other model it does not. A headlong search algorithm is used to explore the model space and select clustering variables. In simulated datasets we found that the method selected the correct clustering variables, and also led to improvements in classification performance and in accuracy of the choice of the number of classes. In two real datasets, our method discovered the same group structure with fewer variables. In a dataset from the International HapMap Project consisting of 639 single nucleotide polymorphisms (SNPs) from 210 members of different groups, our method discovered the same group structure with a much smaller number of SNP
Admissible rules and the Leibniz hierarchy
This paper provides a semantic analysis of admissible rules
and associated completeness conditions for arbitrary deductive systems,
using the framework of abstract algebraic logic. Algebraizability is not
assumed, so the meaning and signi cance of the principal notions vary
with the level of the Leibniz hierarchy at which they are presented. As
a case study of the resulting theory, the non-algebraizable fragments of
relevance logic are considered.This work is based on research supported in part by
the National Research Foundation of South Africa (UID 85407).https://www.dukeupress.edu/notre-dame-journal-of-formal-logichb2016Mathematics and Applied Mathematic
Tests of Bayesian Model Selection Techniques for Gravitational Wave Astronomy
The analysis of gravitational wave data involves many model selection
problems. The most important example is the detection problem of selecting
between the data being consistent with instrument noise alone, or instrument
noise and a gravitational wave signal. The analysis of data from ground based
gravitational wave detectors is mostly conducted using classical statistics,
and methods such as the Neyman-Pearson criteria are used for model selection.
Future space based detectors, such as the \emph{Laser Interferometer Space
Antenna} (LISA), are expected to produced rich data streams containing the
signals from many millions of sources. Determining the number of sources that
are resolvable, and the most appropriate description of each source poses a
challenging model selection problem that may best be addressed in a Bayesian
framework. An important class of LISA sources are the millions of low-mass
binary systems within our own galaxy, tens of thousands of which will be
detectable. Not only are the number of sources unknown, but so are the number
of parameters required to model the waveforms. For example, a significant
subset of the resolvable galactic binaries will exhibit orbital frequency
evolution, while a smaller number will have measurable eccentricity. In the
Bayesian approach to model selection one needs to compute the Bayes factor
between competing models. Here we explore various methods for computing Bayes
factors in the context of determining which galactic binaries have measurable
frequency evolution. The methods explored include a Reverse Jump Markov Chain
Monte Carlo (RJMCMC) algorithm, Savage-Dickie density ratios, the Schwarz-Bayes
Information Criterion (BIC), and the Laplace approximation to the model
evidence. We find good agreement between all of the approaches.Comment: 11 pages, 6 figure
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