2,182 research outputs found
Defining determinism
The article puts forward a branching - style framework for the analysis of determinism and indeterminism of scientific theories, starting from the core idea that an indeterministic system is one whose present allows for more than one alternative possible future. We describe how a definition of determinism stated in terms of branching models supplements and improves current treatments of determinism of theories of physics. In these treatments, we identify three main approaches: one based on the study of (differential) equations, one based on mappings between temporal realizations, and one based on branching models. We first give an overview of these approaches and show that current orthodoxy advocates a combination of the mapping- and the equations - based approaches. After giving a detailed formal explication of a branching - based definition of determinism, we consider three concrete applications and end with a formal comparison of the branching- and the mapping-based approach. We conclude that the branching - based definition of determinism most usefully combines formal clarity, connection with an underlying philosophical notion of determinism, and relevance for the practical assessment of theories
A Protocol for Cast-as-Intended Verifiability with a Second Device
Numerous institutions, such as companies, universities, or non-governmental
organizations, employ Internet voting for remote elections. Since the main
purpose of an election is to determine the voters' will, it is fundamentally
important to ensure that the final election result correctly reflects the
voters' votes. To this end, modern secure Internet voting schemes aim for what
is called end-to-end verifiability. This fundamental security property ensures
that the correctness of the final result can be verified, even if some of the
computers or parties involved are malfunctioning or corrupted.
A standard component in this approach is so called cast-as-intended
verifiability which enables individual voters to verify that the ballots cast
on their behalf contain their intended choices. Numerous approaches for
cast-as-intended verifiability have been proposed in the literature, some of
which have also been employed in real-life Internet elections.
One of the well established approaches for cast-as-intended verifiability is
to employ a second device which can be used by voters to audit their submitted
ballots. This approach offers several advantages - including support for
flexible ballot/election types and intuitive user experience - and it has been
used in real-life elections, for instance in Estonia.
In this work, we improve the existing solutions for cast-as-intended
verifiability based on the use of a second device. We propose a solution which,
while preserving the advantageous practical properties sketched above, provides
tighter security guarantees. Our method does not increase the risk of
vote-selling when compared to the underlying voting protocol being augmented
and, to achieve this, it requires only comparatively weak trust assumptions. It
can be combined with various voting protocols, including commitment-based
systems offering everlasting privacy
Magnetorotational Instability in Core-Collapse Supernovae
We discuss the relevance of the magnetorotational instability (MRI) in
core-collapse supernovae (CCSNe). Our recent numerical studies show that in
CCSNe, the MRI is terminated by parasitic instabilities of the Kelvin-Helmholtz
type. To determine whether the MRI can amplify initially weak magnetic fields
to dynamically relevant strengths in CCSNe, we performed three-dimensional
simulations of a region close to the surface of a differentially rotating
proto-neutron star in non-ideal magnetohydrodynamics with two different
numerical codes. We find that under the conditions prevailing in proto-neutron
stars, the MRI can amplify the magnetic field by (only) one order of magnitude.
This severely limits the role of MRI channel modes as an agent amplifying the
magnetic field in proto-neutron stars starting from small seed fields.Comment: Proceedings in Acta Physica Polonica B, Proceedings Supplement, Vol.
10, No. 2, p.361, 4 pages, 1 figur
New foundations for branching space-times
The theory of branching space-times, put forward by Belnap (Synthese 92, 1992), considers indeterminism as local in space and time. In the axiomatic foundations of that theory, so-called choice points mark the points at which the (local) possible future can turn out in different ways. Working under the assumption of choice points is suitable for many applications, but has an unwelcome topological consequence that makes it difficult to employ branching space-times to represent a range of possible physical space-times.
Therefore it is interesting to develop a branching space-times theory without choice points. This is what we set out to do in this paper, providing new foundations for branching spacetimes in terms of choice sets rather than choice points. After motivating and developing the resulting theory in formal detail, we show that it is possible to translate structures of one style into structures of the other style and vice versa. This result shows that the underlying idea of indeterminism as the branching of spatio-temporal histories is robust with respect to different implementations, making a choice between them a matter of expediency rather than of principle
Growth patterns of the pan‐European freshwater mussel, Anodonta anatina (Linnaeus, 1758) (Bivalvia: Unionidae), vary with sex and mortality in populations
Coherent Backscattering of Ultracold Matter Waves: Momentum Space Signatures
Using analytical and numerical methods, it is shown that the momentum
distribution of a matter wave packet launched in a random potential exhibits a
pronounced coherent backscattering (CBS) peak. By analyzing the momentum
distribution, key transport times can be directly measured. The CBS peak can be
used to prove that transport occurs in the phase-coherent regime, and measuring
its time dependence permits monitoring the transition from classical diffusion
to Anderson localization.Comment: 4 pages, 4 figure
SHEARING TESTS APPLIED TO PANTOGRAPHIC STRUCTURES
With the advancements in 3D printing technology, rapid manufacturing of fabric materials with complex geometries became possible. By exploiting this technique, different materials with different structures have been developed in the recent past with the objective of making generalized continuum theories useful for technological applications. So-called pantographic structures are introduced: Inextensible fibers are printed in two arrays orthogonal to each other in parallel planes. These superimposed planes are inter-connected by elastic cylinders. Five differently-sized samples were subjected to shear-like loading while their deformation response was analyzed. Results show that deformation behavior is strong non-linear for all samples. Furthermore, all samples were capable to resist considerable external shear loads without leading to complete failure of the whole structure. This extraordinary behavior makes these structures attractive to serve as an extremely tough metamaterial
Factors affecting trematode infection rates in freshwater mussels
Mussels are intermediate hosts of digenean trematodes, but determinants of these infections remain unknown. To address this problem, we collected duck mussels Anodonta anatina in eighteen lakes from northeastern Poland and examined how
mussel age, sex, and the encrustation with zebra mussels Dreissena polymorpha and environmental conditions in lakes influenced infection rates. We also assessed parasitic preferences to host gonads and hepatopancreas and the impact of parasites on female fertility. Mussels were infected with Rhipidocotyle campanula and Phyllodistomum sp. Infection rates were higher in older and female mussels but were unrelated to the biomass of encrusting D. polymorpha and the trophy, thermal conditions, and Ca2? availability. Parasites occupied gonads more often than hepatopancreas. Infected females were less likely to carry glochidia and incubated fewer glochidia. We suggest that the risk of infection by digenean trematodes increases with the amount of water processed by filter-feeding hosts and/or that parasites actively seek hosts which can provide them with abundant
resources. This mechanism explains why parasites more often occupied older and female mussels and targeted their gonads. Future research on trematodemussel
interactions should integrate knowledge on different elements of the complex trematode life cycles, including effects of higher-order hosts such as fish
Changes in European eel ovary development and body and ovary chemistry during stimulated maturation under controlled conditions -preliminary data
This study compared changes in the biochemical composition of muscles and ovaries of maturing female European eels during hormonal stimulation with carp pituitary homogenate under controlled conditions and in the development of oocytes. It has been found that differentiation of oocyte size in eel is visible from the beginning of the gamete maturation process. This differentiation increases as gonads grow. Furthermore, oocytes are at different development stages and are still highly differentiated in terms of size during
ovulation. Moreover, the biochemical composition of the body and gonads was found to change. During the process of maturation, the relative fat content in the eel body decreases both in the muscles (from 21.99 ± 4.3 to 18.48 ± 3.3 %) and in gonads (from 25.76 ± 2.71 to 15.21 ± 4.7 %), with the changes in ovaries being more rapid. Protein
content in muscles also decreased (from 15.98 ± 3.13 to 12.35 ± 1.6 %) during the process of female maturation. Different trends were observed for polyunsaturated fatty
acids (EPA and DHA). The total amount of these acids decreased in muscles (P\0.05) but increased in ovaries (P[0.05)
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