2,727 research outputs found
Regression calibration for Cox regression under heteroscedastic measurement error - Determining risk factors of cardiovascular diseases from error-prone nutritional replication data
For instance nutritional data are often subject to severe measurement error, and an adequate adjustment of the estimators is indispensable to avoid deceptive conclusions. This paper discusses and extends the method of regression calibration to correct for measurement error in Cox regression. Special attention is paid to the modelling of quadratic predictors, the role of heteroscedastic measurement error, and the efficient use of replicated measurements of the surrogates. The method is used to analyze data from the German part of the MONICA cohort study on cardiovascular diseases. The results corroborate the importance of taking into account measurement error carefully
A Topos Foundation for Theories of Physics: III. The Representation of Physical Quantities With Arrows
This paper is the third in a series whose goal is to develop a fundamentally
new way of viewing theories of physics. Our basic contention is that
constructing a theory of physics is equivalent to finding a representation in a
topos of a certain formal language that is attached to the system. In paper II,
we studied the topos representations of the propositional language PL(S) for
the case of quantum theory, and in the present paper we do the same thing for
the, more extensive, local language L(S). One of the main achievements is to
find a topos representation for self-adjoint operators. This involves showing
that, for any physical quantity A, there is an arrow
\breve{\delta}^o(A):\Sig\map\SR, where \SR is the quantity-value object for
this theory. The construction of is an extension of the
daseinisation of projection operators that was discussed in paper II. The
object \SR is a monoid-object only in the topos, , of the theory,
and to enhance the applicability of the formalism, we apply to \SR a topos
analogue of the Grothendieck extension of a monoid to a group. The resulting
object, \kSR, is an abelian group-object in . We also discuss
another candidate, \PR{\mathR}, for the quantity-value object. In this
presheaf, both inner and outer daseinisation are used in a symmetric way.
Finally, there is a brief discussion of the role of unitary operators in the
quantum topos scheme.Comment: 38 pages, no figure
Into the wild? How a film can change adolescents' values
In adolescence, behavior and attitudes are constantly rethought and value priorities are established. Still, there is hardly any research addressing how values are shaped throughout this sensitive period. We employed an experimental design, testing whether adolescentsâ values can be influenced by exposure to a film. In our study, 154 German adolescents (80 females, ages 13-15) were randomly assigned to an experimental group that watched excerpts from the film âInto the wildâ or to a control group. Value change was assessed in a pre-post-test design with a one-week interval. As hypothesized, values changed in the direction of those displayed by the filmâs protagonist: Universalism values increased significantly and conformity values decreased significantly as compared to the control group. Our findings suggest that single exposure to a film may initiate value change, indicating that not only major live events, but also everyday experiences significantly affect adolescentsâ values
A Topos Foundation for Theories of Physics: IV. Categories of Systems
This paper is the fourth in a series whose goal is to develop a fundamentally
new way of building theories of physics. The motivation comes from a desire to
address certain deep issues that arise in the quantum theory of gravity. Our
basic contention is that constructing a theory of physics is equivalent to
finding a representation in a topos of a certain formal language that is
attached to the system. Classical physics arises when the topos is the category
of sets. Other types of theory employ a different topos. The previous papers in
this series are concerned with implementing this programme for a single system.
In the present paper, we turn to considering a collection of systems: in
particular, we are interested in the relation between the topos representation
for a composite system, and the representations for its constituents. We also
study this problem for the disjoint sum of two systems. Our approach to these
matters is to construct a category of systems and to find a topos
representation of the entire category.Comment: 38 pages, no figure
Topos quantum theory with short posets
Topos quantum mechanics, developed by Isham et. al., creates a topos of
presheaves over the poset V(N) of abelian von Neumann subalgebras of the von
Neumann algebra N of bounded operators associated to a physical system, and
established several results, including: (a) a connection between the
Kochen-Specker theorem and the non-existence of a global section of the
spectral presheaf; (b) a version of the spectral theorem for self-adjoint
operators; (c) a connection between states of N and measures on the spectral
presheaf; and (d) a model of dynamics in terms of V(N). We consider a
modification to this approach using not the whole of the poset V(N), but only
its elements of height at most two. This produces a different topos with
different internal logic. However, the core results (a)--(d) established using
the full poset V(N) are also established for the topos over the smaller poset,
and some aspects simplify considerably. Additionally, this smaller poset has
appealing aspects reminiscent of projective geometry.Comment: 14 page
Biotic indicators of carabid species richness on organically and conventionally managed arable fields
Carabids, a species rich arthropod family, potentially contribute much to biodiversity in agroecosystems, but assessing and monitoring carabid diversity is costly and time consuming. Therefore, this study aimed at finding more easily measurable parameters indicating high carabid diversity within organic and conventional management systems. Cover and number of weed species as well as activity density of single carabid species and of total carabids were investigated as potential indicators of carabid species richness. The study was carried out near Reckenfeld in Westphalia on sandy Plaggenesch soils. Three organically and four conventionally managed fields (cereals and corn) were investigated at the field margins and in the field centres from April to August 1999. Additionally, data of carabid catches and weed flora in winter cereals from an extended study in DĂŒren (Northrhine-Westphalia) were reanalysed to validate the results. However, neither of the potential indicators showed consistently significant positive correlation with carabid diversity. This is partly attributed to the low variability of management conditions within the management systems in the studies presented
Development of Intra-Individual Value Structures in Middle-Childhood: A Multicultural and Longitudinal Investigation
Introduction
We examined changes in value inter-relations during middle-childhood. In line with the Personal Values Theory (Schwartz, 1992), we expected a value system, with individuals similarly valuing related motivations, and setting priorities between conflicting motivations (Döring et al., 2016; Schwartz, 1992). We hypothesized this system to develop dynamically during middle-childhood, as children deepen their understanding of their own values (Shachnai & Daniel, 2020).
Method
Using unfolding analysis (Borg et al., 2017; Skimina et al., 2021), we estimated intra-individual value structure coherence, i.e., the extent to which the inter-relations among a childâs values are similar to the hypothesized inter-relations. Cross-Cultural Study 1 (N=â4,615 6-12-year-old children) included children from 12 countries. Cross-Sequential Study 2 (N=â629, 6-10-year-old children at Time 1), included three annual measurements.
Results
In Study 1, we found a curvilinear association between age and intra-individual value structure coherence: Childrenâs values were more coherent at ages 9-10 than before or after. Study 2 confirmed this pattern of within-individual development.
Conclusions
We propose that development in coherence with the theoretical value structure offers insight into childrenâs understanding of values as well as changes in value priorities
Charge fluctuations and electric mass in a hot meson gas
Net-Charge fluctuations in a hadron gas are studied using an effective
hadronic interaction. The emphasis of this work is to investigate the
corrections of hadronic interactions to the charge fluctuations of a
non-interacting resonance gas. Several methods, such as loop, density and
virial expansions are employed. The calculations are also extended to SU(3) and
some resummation schemes are considered. Although the various corrections are
sizable individually, they cancel to a large extent. As a consequence we find
that charge fluctuations are rather well described by the free resonance gas.Comment: 32 pages, 18 figure
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