1,526 research outputs found
Sensitivity analysis as an aid in modelling and control of (poorly-defined) ecological systems
A literature review of the use of sensitivity analyses in modelling nonlinear, ill-defined systems, such as ecological interactions is presented. Discussions of previous work, and a proposed scheme for generalized sensitivity analysis applicable to ill-defined systems are included. This scheme considers classes of mathematical models, problem-defining behavior, analysis procedures (especially the use of Monte-Carlo methods), sensitivity ranking of parameters, and extension to control system design
Decoherence in a Talbot Lau interferometer: the influence of molecular scattering
We study the interference of C70 fullerenes in a Talbot-Lau interferometer
with a large separation between the diffraction gratings. This permits the
observation of recurrences of the interference contrast both as a function of
the de Broglie wavelength and in dependence of the interaction with background
gases. We observe an exponential decrease of the fringe visibility with
increasing background pressure and find good quantitative agreement with the
predictions of decoherence theory. From this we extrapolate the limits of
matter wave interferometry and conclude that the influence of collisional
decoherence may be well under control in future experiments with proteins and
even larger objects.Comment: 8 pages, 5 figure
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Mechanical properties and microstructure of In-Ceram, a ceramic-glass composite for dental crowns
The mechanical properties and microstructure of In-Ceram have been investigated. In-Ceram is an alumina-glass composite used for the core of dental crowns produced by infiltrating a glass through a porous alumina skeleton framework. A key property of dental cores besides aesthetic is mechanical strength. The factors affecting strength and microstructure of In-Ceram are discussed in comparison with conventional dental core porcelain. The mean strength of In-Ceram has been found to exceed 600 MPa (ballon- ring tests), but the variance of the measurements is high, demonstrating the importance of the precise preparation of the composite. The influence of aqueous and acidic environment on strength was also studied. The results indicate that In-Ceram, although sensitive to acetic and aqueous environments, combines a level of strength and toughness which should result in an improved clinical performance. EDX-analysis and dilatometry showed that the composition and thermal expansion of the composite phases, glass phase and alumina particles, contribute to the fracture resistance and strength of the composite
Abnormal connectivity between the default mode and the visual system underlies the manifestation of visual hallucinations in Parkinson’s disease:A task-based fMRI study
Background: The neural substrates of visual hallucinations remain an enigma, due primarily to the difficulties associated with directly interrogating the brain during hallucinatory episodes. Aims: To delineate the functional patterns of brain network activity and connectivity underlying visual hallucinations in Parkinson’s disease. Methods: In this study, we combined functional magnetic resonance imaging (MRI) with a behavioral task capable of eliciting visual misperceptions, a confirmed surrogate for visual hallucinations, in 35 patients with idiopathic Parkinson’s disease. We then applied an independent component analysis to extract time series information for large-scale neuronal networks that have been previously implicated in the pathophysiology of visual hallucinations. These data were subjected to a task-based functional connectivity analysis, thus providing the first objective description of the neural activity and connectivity during visual hallucinations in patients with Parkinson’s disease. Results: Correct performance of the task was associated with increased activity in primary visual regions; however, during visual misperceptions, this same visual network became actively coupled with the default mode network (DMN). Further, the frequency of misperception errors on the task was positively correlated with the strength of connectivity between these two systems, as well as with decreased activity in the dorsal attention network (DAN), and with impaired connectivity between the DAN and the DMNs, and ventral attention networks. Finally, each of the network abnormalities identified in our analysis were significantly correlated with two independent clinical measures of hallucination severity. Conclusions: Together, these results provide evidence that visual hallucinations are due to increased engagement of the DMN with the primary visual system, and emphasize the role of dysfunctional engagement of attentional networks in the pathophysiology of hallucinations
Revisiting Orientations in Language Planning: Problem, Right, and Resource as an Analytical Heuristic
In 1984, Richard Ruiz set forth three orientations to language planning: language as problem, language as right, and language as resource. Since that time, the orientations have only become more powerful, rising to the level of paradigm in the field of language policy and planning (LPP). In this paper, we revisit Ruiz’s orientations. By drawing upon Ruiz’s own work as well as the work of other scholars who have been inspired by him, we unpack the ideas aligned with each orientation in order to reflect upon the application of the three orientations as a heuristic for LPP. In contrast to critiques that the three orientations do not map onto the political reality of policy situations, we argue that they are analytically useful as both etic concepts that can be used by researchers to guide deductive analysis about the values that emerge from messy policy debate and negotiation and as (latent) emic concepts in situations when people express their beliefs about language
Decoherence suppression via environment preparation
To protect a quantum system from decoherence due to interaction with its
environment, we investigate the existence of initial states of the environment
allowing for decoherence-free evolution of the system. For models in which a
two-state system interacts with a dynamical environment, we prove that such
states exist if and only if the interaction and self-evolution Hamiltonians
share an eigenstate. If decoherence by state preparation is not possible, we
show that initial states minimizing decoherence result from a delicate
compromise between the environment and interaction dynamics.Comment: 4 pages, 2 figure
Casimir-Polder interaction of fullerene molecules with surfaces
We calculate the thermal Casimir--Polder potential of C60 and C70 fullerene
molecules near gold and silicon nitride surfaces, motivated by their relevance
for molecular matter wave interference experiments. We obtain the coefficients
governing the asymptotic power laws of the interaction in the thermal, retarded
and nonretarded distance regimes and evaluate the full potential numerically.
The interaction is found to be dominated by electronic transitions, and hence
independent of the internal temperature of the molecules. The contributions
from phonon transitions, which are affected by the molecular temperature, give
rise to only a small correction. Moreover, we find that the sizeable molecular
line widths of thermal fullerenes may modify the nonretarded interaction,
depending on the model used. Detailed measurements of the nonretarded potential
of fullerene thus allow one to distinguish between different theories of
incorporating damping.Comment: 9 pages, 8 figures, 9 table
Quechua Language Shift, Maintenance, and Revitalization in the Andes: The Case for Language Planning
Although Quechua is spoken by eight to twelve million people across six South American countries, by most measures, Quechua is an endangered language. This article provides an overview of the current situation of Quechua language shift, maintenance, and revitalization, and makes a case for the importance of language planning for the survival and development of the language. We use Fishman’s notion of physical/demographic, social, and cultural dislocations as an organizing rubric for discussing Quechua’s current situation (Fishman 1991: 55–65), and the typology of status, corpus, and acquisition planning to discuss the role of language planning in Quechua’s position, both current and future. We take into account the role of linguistic ideologies and language attitudes in language shift, maintenance, and revitalization and in the language-planning process, working from the assumption that language is a critical element of ethnic identity for many Quechua speakers in the Andes
Thermal limitation of far-field matter-wave interference
We assess the effect of the heat radiation emitted by mesoscopic particles on
their ability to show interference in a double slit arrangement. The analysis
is based on a stationary, phase-space based description of matter wave
interference in the presence of momentum-exchange mediated decoherence.Comment: 8 pages, 2 figures; published versio
Influence of molecular temperature on the coherence of fullerenes in a near-field interferometer
We study C70 fullerene matter waves in a Talbot-Lau interferometer as a
function of their temperature. While the ideal fringe visibility is observed at
moderate molecular temperatures, we find a gradual degradation of the
interference contrast if the molecules are heated before entering the
interferometer. A method is developed to assess the distribution of the
micro-canonical temperatures of the molecules in free flight. This way the
heating-dependent reduction of interference contrast can be compared with the
predictions of quantum theory. We find that the observed loss of coherence
agrees quantitatively with the expected decoherence rate due to the thermal
radiation emitted by the hot molecules.Comment: 11 pages, 9 figure
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