1,285 research outputs found
Simultaneous inference for misaligned multivariate functional data
We consider inference for misaligned multivariate functional data that
represents the same underlying curve, but where the functional samples have
systematic differences in shape. In this paper we introduce a new class of
generally applicable models where warping effects are modeled through nonlinear
transformation of latent Gaussian variables and systematic shape differences
are modeled by Gaussian processes. To model cross-covariance between sample
coordinates we introduce a class of low-dimensional cross-covariance structures
suitable for modeling multivariate functional data. We present a method for
doing maximum-likelihood estimation in the models and apply the method to three
data sets. The first data set is from a motion tracking system where the
spatial positions of a large number of body-markers are tracked in
three-dimensions over time. The second data set consists of height and weight
measurements for Danish boys. The third data set consists of three-dimensional
spatial hand paths from a controlled obstacle-avoidance experiment. We use the
developed method to estimate the cross-covariance structure, and use a
classification setup to demonstrate that the method outperforms
state-of-the-art methods for handling misaligned curve data.Comment: 44 pages in total including tables and figures. Additional 9 pages of
supplementary material and reference
Statistical modelling of conidial discharge of entomophthoralean fungi using a newly discovered Pandora species
Entomophthoralean fungi are insect pathogenic fungi and are characterized by
their active discharge of infective conidia that infect insects. Our aim was to
study the effects of temperature on the discharge and to characterize the
variation in the associated temporal pattern of a newly discovered Pandora
species with focus on peak location and shape of the discharge. Mycelia were
incubated at various temperatures in darkness, and conidial discharge was
measured over time. We used a novel modification of a statistical model
(pavpop), that simultaneously estimates phase and amplitude effects, into a
setting of generalized linear models. This model is used to test hypotheses of
peak location and discharge of conidia. The statistical analysis showed that
high temperature leads to an early and fast decreasing peak, whereas there were
no significant differences in total number of discharged conidia. Using the
proposed model we also quantified the biological variation in the timing of the
peak location at a fixed temperature.Comment: 23 pages including supplementary materia
Changes of pH in β-Lactoglobulin and β-Casein Solutions during High Pressure Treatment
The pH changes in the milk systems, β-lactoglobulin B, β-casein, and mixture of β-lactoglobulin and β-casein (pH 7 and ionic strength 0.08 M) were measured in situ during increasing pressure up to 500 MPa. An initial decrease to pH 6.7 was observed from 0.1 to 150 MPa for β-lactoglobulin, followed by an increase to pH 7.3 at 500 MPa. The initial decrease is suggested to be caused by the deprotonation of histidine, while the increase is suggested to result from an increase of hydroxide ions due to the loss of tertiary structure. The change in pH of the β-casein solution displayed an almost linear increasing pressure dependency up to a pH of 7.7 at 500 MPa. The limited tertiary structure of β-casein could allow exposure of all amino acids; thus the increase of pH can be caused by binding of water protons resulting in an increase of hydroxide ions. Addition of β-casein to β-lactoglobulin (1:1) was found to suppress the initial pH decrease found for the β-lactoglobulin solution. The pH change of the mixture did not suggest any intermolecular interaction, and a simple additive model is proposed to calculate the pH change of the mixture from the corresponding individual samples
Frequency Dependent Specific Heat from Thermal Effusion in Spherical Geometry
We present a novel method of measuring the frequency dependent specific heat
at the glass transition applied to 5-polyphenyl-4-ether. The method employs
thermal waves effusing radially out from the surface of a spherical thermistor
that acts as both a heat generator and thermometer. It is a merit of the method
compared to planar effusion methods that the influence of the mechanical
boundary conditions are analytically known. This implies that it is the
longitudinal rather than the isobaric specific heat that is measured. As
another merit the thermal conductivity and specific heat can be found
independently. The method has highest sensitivity at a frequency where the
thermal diffusion length is comparable to the radius of the heat generator.
This limits in practise the frequency range to 2-3 decades. An account of the
3omega-technique used including higher order terms in the temperature
dependency of the thermistor and in the power generated is furthermore given.Comment: 17 pages, 15 figures, Substantially revised versio
Impaired transmission in the corticospinal tract and gait disability in spinal cord injured persons
Rehabilitation following spinal cord injury is likely to depend on recovery of corticospinal systems. Here we investigate whether transmission in the corticospinal tract may explain foot drop (inability to dorsiflex ankle) in persons with spinal cord lesion. The study was performed in 24 persons with incomplete spinal cord lesion (C1 to L1) and 15 healthy controls. Coherence in the 10- to 20-Hz frequency band between paired tibialis anterior muscle (TA) electromyographic recordings obtained in the swing phase of walking, which was taken as a measure of motor unit synchronization. It was significantly correlated with the degree of foot drop, as measured by toe elevation and ankle angle excursion in the first part of swing. Transcranial magnetic stimulation was used to elicit motor-evoked potentials (MEPs) in the TA. The amplitude of the MEPs at rest and their latency during contraction were correlated to the degree of foot drop. Spinal cord injured participants who exhibited a large foot drop had little or no MEP at rest in the TA muscle and had little or no coherence in the same muscle during walking. Gait speed was correlated to foot drop, and was the lowest in participants with no MEP at rest. The data confirm that transmission in the corticospinal tract is of importance for lifting the foot during the swing phase of human gait
Urban-rural divides in preferences for wetland conservation in Malaysia
We examined the preferences for wetland conservation among urban and rural dwellers in Malaysia. A choice experiment using face-to-face interviews with urban and rural households was employed. Wetland conservation alternatives were described in terms of environmental protection zones, biodiversity protection, recreational services and flood. Each alternative was connected to a cost for the household, which was a reduction in subsidies for daily goods. Using a latent class model, we identified three groups with distinctly different preferences. The first group comprised mainly rural people with negative willingness to pay for conservation, while the second group included mostly urban people who favored wetland conservation and exhibited positive preference for wetland attributes. The third group was also consisted of mainly urban people who exhibited both negative and positive preferences toward different aspects of conservation. All three groups, however, asserted a strong preference for significant flood risk reduction. The results indicated potential conflicts over wetland conservation impacts and targets. Accordingly, the divide in preferences should be taken into account in policy-making, and the insights provided here may inform efforts to avoid conflict across the population
Beta relaxation in the shear mechanics of equilibrium viscous liquids: Phenomenology and network modeling of the alpha-beta merging region
The phenomenology of the beta relaxation process in the shear-mechanical
response of glass-forming liquids is summarized and compared to that of the
dielectric beta process. Furthermore, we discuss how to model the observations
by means of standard viscoelastic modeling elements. Necessary physical
requirements to such a model are outlined, and it is argued that physically
relevant models must be additive in the shear compliance of the alpha and beta
parts. A model based on these considerations is proposed and fitted to data for
Polyisobutylene 680.Comment: 8 pages, 6 figures, Minor correction
Statistical modelling of conidial discharge of entomophthoralean fungi using a newly discovered Pandora species
Entomophthoralean fungi are insect pathogenic fungi and are characterized by their active discharge of infective conidia that infect insects. Our aim was to study the effects of temperature on the discharge and to characterize the variation in the associated temporal pattern of a newly discovered Pandora species with focus on peak location and shape of the discharge. Mycelia were incubated at various temperatures in darkness, and conidial discharge was measured over time. We used a novel modification of a statistical model (pavpop), that simultaneously estimates phase and amplitude effects, into a setting of generalized linear models. This model is used to test hypotheses of peak location and discharge of conidia. The statistical analysis showed that high temperature leads to an early and fast decreasing peak, whereas there were no significant differences in total number of discharged conidia. Using the proposed model we also quantified the biological variation in the timing of the peak location at a fixed temperature
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