552 research outputs found
Provenance and geochemistry of exotic clasts in conglomerates of the Oligocene Torehina Formation, Coromandel Peninsula, New Zealand
Non-marine pebble to cobble conglomerates of the lower Torehina Formation (Oligocene) crop out along western Coromandel Peninsula and overlie, with strong angular discordance, continental-margin metasedimentary rocks (Manaia Hill Group) of Mesozoic (Late Jurassic to ?Early Cretaceous) age. The conglomerates contain provenance information that identifies a pre-Oligocene depositional history obscured by the unconformable juxtaposition of these Tertiary and Mesozoic strata. Most clasts in the lower Torehina Formation are visually similar to local bedrock lithologies, including metamorphosed sandstones and argillites, but are kaolinitic and contain more detrital and authigenic chert, quartz, and potash feldspar. Local derivation of these clasts seems unlikely. By comparing geochemical ratios with those defined for continental margin sandstones, and well characterised New Zealand tectonic terranes, we interpret the majority of clasts in the lower Torehina Formation to have been derived from a dissected orogen, with mixtures of felsic and volcanogenic-derived sediment. The most likely sources are the Waipapa and Torlesse Terranes. The remaining 20–30% of the clasts in the lower Torehina Formation were originally friable, are coarse grained, and appear to be lithologically exotic relative to known metamorphosed sandstones in basement terrane sources on North Island. Some clasts contain coal laminae and particles, and all contain detrital kaolinite as lithic fragments and matrix. Such characteristics imply a non-marine to marginal-marine source containing sediment derived from strongly weathered granite or granodiorite. Mechanical fragility implies a likely proximal, easily erodible source. We propose that this group of clasts was derived from an Upper Cretaceous sedimentary cover, either part of a locally developed basin fill or part of a once regionally extensive cover on North Island. Either case defines a more widely distributed Cretaceous source than found today
Ab initio studies of phonon softening and high pressure phase transitions of alpha-quartz SiO2
Density functional perturbation theory calculations of alpha-quartz using
extended norm conserving pseudopotentials have been used to study the elastic
properties and phonon dispersion relations along various high symmetry
directions as a function of bulk, uniaxial and non-hydrostatic pressure. The
computed equation of state, elastic constants and phonon frequencies are found
to be in good agreement with available experimental data. A zone boundary (1/3,
1/3, 0) K-point phonon mode becomes soft for pressures above P=32 GPa. Around
the same pressure, studies of the Born stability criteria reveal that the
structure is mechanically unstable. The phonon and elastic softening are
related to the high pressure phase transitions and amorphization of quartz and
these studies suggest that the mean transition pressure is lowered under
non-hydrostatic conditions. Application of uniaxial pressure, results in a
post-quartz crystalline monoclinic C2 structural transition in the vicinity of
the K-point instability. This structure, intermediate between quartz and
stishovite has two-thirds of the silicon atoms in octahedral coordination while
the remaining silicon atoms remain tetrahedrally coordinated. This novel
monoclinic C2 polymorph of silica, which is found to be metastable under
ambient conditions, is possibly one of the several competing dense forms of
silica containing octahedrally coordinated silicon. The possible role of high
pressure ferroelastic phases in causing pressure induced amorphization in
silica are discussed.Comment: 17 pages, 8 figs., 8 Table
Deep Memory Networks for Attitude Identification
We consider the task of identifying attitudes towards a given set of entities
from text. Conventionally, this task is decomposed into two separate subtasks:
target detection that identifies whether each entity is mentioned in the text,
either explicitly or implicitly, and polarity classification that classifies
the exact sentiment towards an identified entity (the target) into positive,
negative, or neutral.
Instead, we show that attitude identification can be solved with an
end-to-end machine learning architecture, in which the two subtasks are
interleaved by a deep memory network. In this way, signals produced in target
detection provide clues for polarity classification, and reversely, the
predicted polarity provides feedback to the identification of targets.
Moreover, the treatments for the set of targets also influence each other --
the learned representations may share the same semantics for some targets but
vary for others. The proposed deep memory network, the AttNet, outperforms
methods that do not consider the interactions between the subtasks or those
among the targets, including conventional machine learning methods and the
state-of-the-art deep learning models.Comment: Accepted to WSDM'1
Applying machine learning to improve simulations of a chaotic dynamical system using empirical error correction
Dynamical weather and climate prediction models underpin many studies of the
Earth system and hold the promise of being able to make robust projections of
future climate change based on physical laws. However, simulations from these
models still show many differences compared with observations. Machine learning
has been applied to solve certain prediction problems with great success, and
recently it's been proposed that this could replace the role of
physically-derived dynamical weather and climate models to give better quality
simulations. Here, instead, a framework using machine learning together with
physically-derived models is tested, in which it is learnt how to correct the
errors of the latter from timestep to timestep. This maintains the physical
understanding built into the models, whilst allowing performance improvements,
and also requires much simpler algorithms and less training data. This is
tested in the context of simulating the chaotic Lorenz '96 system, and it is
shown that the approach yields models that are stable and that give both
improved skill in initialised predictions and better long-term climate
statistics. Improvements in long-term statistics are smaller than for single
time-step tendencies, however, indicating that it would be valuable to develop
methods that target improvements on longer time scales. Future strategies for
the development of this approach and possible applications to making progress
on important scientific problems are discussed.Comment: 26p, 7 figures To be published in Journal of Advances in Modeling
Earth System
Modeling Long-Range Context for Concurrent Dialogue Acts Recognition
In dialogues, an utterance is a chain of consecutive sentences produced by
one speaker which ranges from a short sentence to a thousand-word post. When
studying dialogues at the utterance level, it is not uncommon that an utterance
would serve multiple functions. For instance, "Thank you. It works great."
expresses both gratitude and positive feedback in the same utterance. Multiple
dialogue acts (DA) for one utterance breeds complex dependencies across
dialogue turns. Therefore, DA recognition challenges a model's predictive power
over long utterances and complex DA context. We term this problem Concurrent
Dialogue Acts (CDA) recognition. Previous work on DA recognition either assumes
one DA per utterance or fails to realize the sequential nature of dialogues. In
this paper, we present an adapted Convolutional Recurrent Neural Network (CRNN)
which models the interactions between utterances of long-range context. Our
model significantly outperforms existing work on CDA recognition on a tech
forum dataset.Comment: Accepted to CIKM '1
An Exploratory Analysis of the Latent Structure of Process Data via Action Sequence Autoencoder
Computer simulations have become a popular tool of assessing complex skills
such as problem-solving skills. Log files of computer-based items record the
entire human-computer interactive processes for each respondent. The response
processes are very diverse, noisy, and of nonstandard formats. Few generic
methods have been developed for exploiting the information contained in process
data. In this article, we propose a method to extract latent variables from
process data. The method utilizes a sequence-to-sequence autoencoder to
compress response processes into standard numerical vectors. It does not
require prior knowledge of the specific items and human-computers interaction
patterns. The proposed method is applied to both simulated and real process
data to demonstrate that the resulting latent variables extract useful
information from the response processes.Comment: 28 pages, 13 figure
A combined XAS and XRD Study of the High-Pressure Behaviour of GaAsO4 Berlinite
Combined X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD)
experiments have been carried out on GaAsO4 (berlinite structure) at high
pressure and room temperature. XAS measurements indicate four-fold to six-fold
coordination changes for both cations. The two local coordination
transformations occur at different rates but appear to be coupled. A reversible
transition to a high pressure crystalline form occurs around 8 GPa. At a
pressure of about 12 GPa, the system mainly consists of octahedral gallium
atoms and a mixture of arsenic in four-fold and six-fold coordinations. A
second transition to a highly disordered material with both cations in six-fold
coordination occurs at higher pressures and is irreversible.Comment: 8 pages, 5 figures, LaTeX2
The walking speed-dependency of gait variability in bilateral vestibulopathy and its association with clinical tests of vestibular function
Understanding balance and gait deficits in vestibulopathy may help improve clinical care and our knowledge of the vestibular contributions to balance. Here, we examined walking speed effects on gait variability in healthy adults and in adults with bilateral vestibulopathy (BVP). Forty-four people with BVP, 12 healthy young adults and 12 healthy older adults walked at 0.4m/s to 1.6m/s in 0.2m/s increments on a dual belt, instrumented treadmill. Using motion capture and kinematic data, the means and coefficients of variation for step length, time, width and double support time were calculated. The BVP group also completed a video head impulse test and examinations of ocular and cervical vestibular evoked myogenic potentials and dynamic visual acuity. Walking speed significantly affected all gait parameters. Step length variability at slower speeds and step width variability at faster speeds were the most distinguishing parameters between the healthy participants and people with BVP, and among people with BVP with different locomotor capacities. Step width variability, specifically, indicated an apparent persistent importance of vestibular function at increasing speeds. Gait variability was not associated with the clinical vestibular tests. Our results indicate that gait variability at multiple walking speeds has potential as an assessment tool for vestibular interventions
Symptom-led staging for semantic and non-fluent/agrammatic variants of primary progressive aphasia. Alzheimer's & Dementia
INTRODUCTION: Here we set out to create a symptom-led staging system for the
canonical semantic and non-fluent/agrammatic variants of primary progressive aphasia (PPA), which present unique diagnostic and management challenges not well captured by functional scales developed for Alzheimer’s disease and other dementias.
METHODS: An international PPA caregiver cohort was surveyed on symptom development under six provisional clinical stages and feedback was analyzed using a mixed-methods sequential explanatory design.
RESULTS: Both PPA syndromes were characterized by initial communication dysfunction and non-verbal behavioral changes, with increasing syndromic convergence and functional dependency at later stages. Milestone symptoms were distilled to create a prototypical progression and severity scale of functional impairment: the PPA Progression Planning Aid (“PPA-Squared”).
DISCUSSION: This work introduces a symptom-led staging scheme and functional
scale for semantic and non-fluent/agrammatic variants of PPA. Our findings have implications for diagnostic and care pathway guidelines, trial design, and personalized prognosis and treatment for PPA
Symptom-based staging for logopenic variant primary progressive aphasia
Background and purpose
Logopenic variant primary progressive aphasia (lvPPA) is a major variant presentation of Alzheimer's disease (AD) that signals the importance of communication dysfunction across AD phenotypes. A clinical staging system is lacking for the evolution of AD-associated communication difficulties that could guide diagnosis and care planning. Our aim was to create a symptom-based staging scheme for lvPPA, identifying functional milestones relevant to the broader AD spectrum.
Methods
An international lvPPA caregiver cohort was surveyed on symptom development under an ‘exploratory’ survey (34 UK caregivers). Feedback from this survey informed the development of a ‘consolidation’ survey (27 UK, 10 Australian caregivers) in which caregivers were presented with six provisional clinical stages and feedback was analysed using a mixed-methods approach.
Results
Six clinical stages were endorsed. Early symptoms included word-finding difficulty, with loss of message comprehension and speech intelligibility signalling later-stage progression. Additionally, problems with hearing in noise, memory and route-finding were prominent early non-verbal symptoms. ‘Milestone’ symptoms were identified that anticipate daily-life functional transitions and care needs.
Conclusions
This work introduces a new symptom-based staging scheme for lvPPA, and highlights milestone symptoms that could inform future clinical scales for anticipating and managing communication dysfunction across the AD spectrum
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