1,336 research outputs found
Body-rock or lift-off in flow
Conditions are investigated under which a body lying at rest or rocking on a
solid horizontal surface can be removed from the surface by hydrodynamic forces
or instead continues rocking. The investigation is motivated by recent
observations on Martian dust movement as well as other small- and large-scale
applications. The nonlinear theory of fluid-body interaction here has unsteady
motion of an inviscid fluid interacting with a moving thin body. Various shapes
of body are addressed together with a range of initial conditions. The relevant
parameter space is found to be subtle as evolution and shape play substantial
roles coupled with scaled mass and gravity effects. Lift-off of the body from
the surface generally cannot occur without fluid flow but it can occur either
immediately or within a finite time once the fluid flow starts up: parameters
for this are found and comparisons are made with Martian observations.Comment: 28 pages, 9 figure
Quantum Immortality and Non-Classical Logic
The Everett Box is a device in which an observer and a lethal quantum
apparatus are isolated from the rest of the universe. On a regular basis,
successive trials occur, in each of which an automatic measurement of a quantum
superposition inside the apparatus either causes instant death or does nothing
to the observer. From the observer's perspective, the chances of surviving
trials monotonically decreases with increasing . As a result, if the
observer is still alive for sufficiently large she must reject any
interpretation of quantum mechanics which is not the many-worlds interpretation
(MWI), since surviving trials becomes vanishingly unlikely in a single
world, whereas a version of the observer will necessarily survive in the
branching MWI universe. Here we ask whether this conclusion still holds if
rather than a classical understanding of limits built on classical logic we
instead require our physics to satisfy a computability requirement by
investigating the Everett Box in a model of a computational universe running on
a variety of constructive logic, Recursive Constructive Mathematics. We show
that although the standard Everett argument rejecting non-MWI interpretations
is no longer valid, we can show that Everett's conclusion still holds within a
computable universe. Thus we argue that Everett's argument is strengthened and
any counter-argument must be strengthened, since it holds not only in classical
logic (with embedded notions of continuity and infinity) but also in a
computable logic.Comment: 12 page
Infinity in computable probability
Does combining a finite collection of objects infinitely many times guarantee
the construction of a particular object? Here we use recursive function theory
to examine the popular scenario of an infinite collection of typing monkeys
reproducing the works of Shakespeare. Our main result is to show that it is
possible to assign typing probabilities in such a way that while it is
impossible that no monkey reproduces Shakespeare's works, the probability of
any finite collection of monkeys doing so is arbitrarily small. We extend our
results to target-free writing, and end with a broad discussion and pointers to
future work
The Qualitative Interview in Psychology and the Study of Social Change: Sexual Identity Development, Minority Stress, and Health in the Generations Study.
Interviewing is considered a key form of qualitative inquiry in psychology that yields rich data on lived experience and meaning making of life events. Interviews that contain multiple components informed by specific epistemologies have the potential to provide particularly nuanced perspectives on psychological experience. We offer a methodological model for a multi-component interview that draws upon both pragmatic and constructivist epistemologies to examine generational differences in the experience of identity development, stress, and health among contemporary sexual minorities in the United States. Grounded in theories of life course, narrative, and intersectionality, we designed and implemented a multi-component protocol that was administered among a diverse sample of three generations of sexual minority individuals. For each component, we describe the purpose and utility, underlying epistemology, foundational psychological approach, and procedure, and we provide illustrative data from interviewees. We discuss procedures undertaken to ensure methodological integrity in process of data collection, illustrating the implementation of recent guidelines for qualitative inquiry in psychology. We highlight the utility of this qualitative multi-component interview to examine the way in which sexual minorities of distinct generations have made meaning of significant social change over the past half-century
Partial differential equation models for invasive species spread in the presence of spatial heterogeneity
Models of invasive species spread often assume that landscapes are spatially
homogeneous; thus simplifying analysis but potentially reducing accuracy. We
extend a recently developed partial differential equation model for invasive
conifer spread to account for spatial heterogeneity in parameter values and
introduce a method to obtain key outputs (e.g. spread rates) from computational
simulations. Simulations produce patterns of spatial spread remarkably similar
to observed patterns in grassland ecosystems invaded by exotic conifers,
validating our spatially explicit strategy. We find that incorporating spatial
variation in different parameters does not significantly affect the evolution
of invasions (which are characterised by a long quiescent period followed by
rapid evolution towards to a constant rate of invasion) but that distributional
assumptions can have a significant impact on the spread rate of invasions. Our
work demonstrates that spatial variation in site-suitability or other
parameters can have a significant impact on invasionsComment: 13 pages, 18 figure
Not so distinctively mathematical explanations: topology and dynamical systems
So-called ‘distinctively mathematical explanations’ (DMEs) are said to explain physical phenomena, not in terms of contingent causal laws, but rather in terms of mathematical necessities that constrain the physical system in question. Lange argues that the existence of four or more equilibrium positions of any double pendulum has a DME. Here we refute both Lange’s claim itself and a strengthened and extended version of the claim that would pertain to any n-tuple pendulum system on the ground that such explanations are actually causal explanations in disguise and their associated modal conditionals are not general enough to explain the said features of such dynamical systems. We argue and show that if circumscribing the antecedent for a necessarily true conditional in such explanations involves making a causal analysis of the problem, then the resulting explanation is not distinctively mathematical or non-causal. Our argument generalises to other dynamical systems that may have purported DMEs analogous to the one proposed by Lange, and even to some other counterfactual accounts of non-causal explanation given by Reutlinger and Rice
On the continuum fallacy: is temperature a continuous function?
It is often argued that the indispensability of continuum models comes from their empirical adequacy despite their decoupling from the microscopic details of the modelled physical system. There is thus a commonly held misconception that temperature varying across a region of space or time can always be accurately represented as a continuous function. We discuss three inter-related cases of temperature modelling — in phase transitions, thermal boundary resistance and slip flows — and show that the continuum view is fallacious on the ground that the microscopic details of a physical system are not necessarily decoupled from continuum models. We show how temperature discontinuities are present in both data (experiments and simulations) and phenomena (theory and models) and how discontinuum models of temperature variation may have greater empirical adequacy and explanatory power. The conclusions of our paper are: a) continuum idealisations are not indispensable to modelling physical phenomena and both continuous and discontinuous representations of phenomena work depending on the context; b) temperature is not necessarily a continuously defined function in our best scientific representations of the world; and c) that its continuity, where applicable, is a contingent matter. We also raise a question as to whether discontinuous representations should be considered truly de-idealised descriptions of physical phenomena
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The Breathe Easier through Weight Loss Lifestyle (BE WELL) Intervention: A randomized controlled trial
<p>Abstract</p> <p>Background</p> <p>Obesity and asthma have reached epidemic proportions in the US. Their concurrent rise over the last 30 years suggests that they may be connected. Numerous observational studies support a temporally-correct, dose-response relationship between body mass index (BMI) and incident asthma. Weight loss, either induced by surgery or caloric restriction, has been reported to improve asthma symptoms and lung function. Due to methodological shortcomings of previous studies, however, well-controlled trials are needed to investigate the efficacy of weight loss strategies to improve asthma control in obese individuals.</p> <p>Methods/Design</p> <p>BE WELL is a 2-arm parallel randomized clinical trial (RCT) of the efficacy of an evidence-based, comprehensive, behavioral weight loss intervention, focusing on diet, physical activity, and behavioral therapy, as adjunct therapy to usual care in the management of asthma in obese adults. Trial participants (n = 324) are patients aged 18 to 70 years who have suboptimally controlled, persistent asthma, BMI between 30.0 and 44.9 kg/m<sup>2</sup>, and who do not have serious comorbidities (e.g., diabetes, heart disease, stroke). The 12-month weight loss intervention to be studied is based on the principles of the highly successful Diabetes Prevention Program lifestyle intervention. Intervention participants will attend 13 weekly group sessions over a four-month period, followed by two monthly individual sessions, and will then receive individualized counseling primarily by phone, at least bi-monthly, for the remainder of the intervention. Follow-up assessment will occur at six and 12 months. The primary outcome variable is the overall score on the Juniper Asthma Control Questionnaire measured at 12 months. Secondary outcomes include lung function, asthma-specific and general quality of life, asthma medication use, asthma-related and total health care utilization. Potential mediators (e.g., weight loss and change in physical activity level and nutrient intake) and moderators (e.g., socio-demographic characteristics and comorbidities) of the intervention effects also will be examined.</p> <p>Discussion</p> <p>This RCT holds considerable potential for illuminating the nature of the obesity-asthma relationship and advancing current guidelines for treating obese adults with asthma, which may lead to reduced morbidity and mortality related to the comorbidity of the two disorders.</p> <p>Trial registration</p> <p>NCT00901095</p
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