980 research outputs found
An independent axiomatisation for free short-circuit logic
Short-circuit evaluation denotes the semantics of propositional connectives
in which the second argument is evaluated only if the first argument does not
suffice to determine the value of the expression. Free short-circuit logic is
the equational logic in which compound statements are evaluated from left to
right, while atomic evaluations are not memorised throughout the evaluation,
i.e., evaluations of distinct occurrences of an atom in a compound statement
may yield different truth values. We provide a simple semantics for free SCL
and an independent axiomatisation. Finally, we discuss evaluation strategies,
some other SCLs, and side effects.Comment: 36 pages, 4 tables. Differences with v2: Section 2.1: theorem
Thm.2.1.5 and further are renumbered; corrections: p.23, line -7, p.24, lines
3 and 7. arXiv admin note: substantial text overlap with arXiv:1010.367
Propositional logic with short-circuit evaluation: a non-commutative and a commutative variant
Short-circuit evaluation denotes the semantics of propositional connectives
in which the second argument is evaluated only if the first argument does not
suffice to determine the value of the expression. Short-circuit evaluation is
widely used in programming, with sequential conjunction and disjunction as
primitive connectives.
We study the question which logical laws axiomatize short-circuit evaluation
under the following assumptions: compound statements are evaluated from left to
right, each atom (propositional variable) evaluates to either true or false,
and atomic evaluations can cause a side effect. The answer to this question
depends on the kind of atomic side effects that can occur and leads to
different "short-circuit logics". The basic case is FSCL (free short-circuit
logic), which characterizes the setting in which each atomic evaluation can
cause a side effect. We recall some main results and then relate FSCL to MSCL
(memorizing short-circuit logic), where in the evaluation of a compound
statement, the first evaluation result of each atom is memorized. MSCL can be
seen as a sequential variant of propositional logic: atomic evaluations cannot
cause a side effect and the sequential connectives are not commutative. Then we
relate MSCL to SSCL (static short-circuit logic), the variant of propositional
logic that prescribes short-circuit evaluation with commutative sequential
connectives.
We present evaluation trees as an intuitive semantics for short-circuit
evaluation, and simple equational axiomatizations for the short-circuit logics
mentioned that use negation and the sequential connectives only.Comment: 34 pages, 6 tables. Considerable parts of the text below stem from
arXiv:1206.1936, arXiv:1010.3674, and arXiv:1707.05718. Together with
arXiv:1707.05718, this paper subsumes most of arXiv:1010.367
An instability mechanism for particulate pipe flow
We present linear stability analysis for a simple model of particle-laden
pipe flow. The model consists of a continuum approximation for the particles
two-way coupled to the fluid velocity field via Stokes drag (Saffman 1962). We
extend previous analysis in a channel (Klinkenberg et al. 2011) to allow for
the initial distribution of particles to be inhomogeneous and in particular
consider the effect of allowing the particles to be preferentially located
around one radius in accordance with experimental observations. This simple
modification of the problem is enough to alter the stability properties of the
flow, and in particular can lead to a linear instability at experimentally
realistic parameters. The results are compared to the experimental work of
Matas et al. (2004a) and are shown to be consistent with the reported flow
regimes.Comment: 15 pages, 11 figure
Ranking of food safety risks in pork from organic and free-range production systems
The objectives of this semi-quantitative risk assessment were to identify, assess and rank food safety risks in outdoor pig production (organic and free-range) compared to indoor pig production (conventional) in Denmark. In addition, high-risk pork products would be identified. Finally, risk-reducing strategies for handling the identified agents would be suggested. Data were obtained from the literature as well as in-house statistics. Data describing tetracycline-resistant E. coli in outdoor pigs were available from the Qualysafe project. The OIE framework for risk assessment was applied
Design of a carbon fiber suspension system for FSAE applications
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 35).Reducing weight while maintaining structural integrity is one of the key challenges Formula SAE teams face as they try and design the suspension of the formula car. The purpose of this paper is to present experimental data on designing and optimizing a carbon fiber suspension system for formula cars. The reason carbon fiber suspensions are favored over the current steel suspensions is because of they can reduce the weight of the suspension by 50%. Pull tests on an Instron machine were performed on over 15 specimens composed of a carbon fiber tube with an aluminum insert bonded to each end. Loctite E-120HP epoxy was used and the surface preparation, bond gap, and bond length were varied to find the optimal bond strength. An average bond strength of 2,382.6 pounds per square inch was determined for specimens with surface preparation. Furthermore a bond gap of 0.0065 to 0.008 inches was found to give the strongest bond.by Alban C. Cobi.S.B
Clogging by sieving in microchannels: Application to the detection of contaminants in colloidal suspensions
We report on a microfluidic method that allows measurement of a small
concentration of large contaminants in suspensions of solid micrometer-scale
particles. To perform the measurement, we flow the colloidal suspension through
a series of constrictions, i.e. a microchannel of varying cross-section. We
show and quantify the role of large contaminants in the formation of clogs at a
constriction and the growth of the resulting filter cake. By measuring the time
interval between two clogging events in an array of parallel microchannels, we
are able to estimate the concentration of contaminants whose size is selected
by the geometry of the microfluidic device. This technique for characterizing
colloidal suspensions offers a versatile and rapid tool to explore the role of
contaminants on the properties of the suspensions
Seagrass biofilm communities at a naturally CO2-rich vent
Seagrass meadows are a crucial component of tropical marine reef ecosystems. Seagrass plants are colonized by a multitude of epiphytic organisms that contribute to broadening the ecological role of seagrasses. To better understand how environmental changes like ocean acidification might affect epiphytic assemblages, the microbial community composition of the epiphytic biofilm of Enhalus acroides was investigated at a natural CO2 vent in Papua New Guinea using molecular fingerprinting and next generation sequencing of 16S and 18S rRNA genes. Both bacterial and eukaryotic epiphytes formed distinct communities at the CO2-impacted site compared to the control site. This site-related CO2 effect was also visible in the succession pattern of microbial epiphytes. We further found an increased abundance of bacterial types associated with coral diseases at the CO2-impacted site (Fusobacteria, Thalassomonas) whereas eukaryotes such as certain crustose coralline algae commonly related to healthy reefs were less diverse. These trends in the epiphytic community of E. acroides suggest a potential role of seagrasses as vectors of coral pathogens and may support previous predictions of a decrease in reef health and prevalence of diseases under future ocean acidification scenarios
Risk-mitigation for antimicrobial resistance in Danish swine herds at a national level
In Denmark, actions to mitigate the risk related to antimicrobial resistance have been put in place continuously. Due to an increase in the consumption of antimicrobials in the Danish pig production further actions were implemented in July 2010. These were: a voluntary ban on use of cephalosporin in Danish swine herds for a 2-year period and a so-called “Yellow card” scheme from the Danish Veterinary and Food Administration (DVFA). Farmers with the highest use of antibiotics receive a Yellow Card. Approximately 10% of Danish herds are above the yellow card threshold value. The consumption in pigs is evaluated as animal daily doses (ADD) per 100 animals seen over the last 9 months (by age group)
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