10,319 research outputs found
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Experimental and bond graph based sensitivity calculations for micro-scale robust engineering design
Copyright @ 2005 IEEEBond graph modeling and sensitivity analysis are used to provide a platform for the robust design of a small mechatronic device, a behind-the-ear (BTE) hearing aid. Two key components of the device, namely the telecoil and the receiver, are considered. Experimental measurements, bond graph simulation models and analytic sensitivity analysis are used to investigate the interaction between these components in order to gain insight into the effect of component placement on the robustness of the final product
Bond graph based sensitivity and uncertainty analysis modelling for micro-scale multiphysics robust engineering design
Components within micro-scale engineering systems are often at the limits of commercial miniaturization and this can cause unexpected behavior and variation in performance. As such, modelling and analysis of system robustness plays an important role in product development. Here schematic bond graphs are used as a front end in a sensitivity analysis based strategy for modelling robustness in multiphysics micro-scale engineering systems. As an example, the analysis is applied to a behind-the-ear (BTE) hearing aid.
By using bond graphs to model power flow through components within different physical domains of the hearing aid, a set of differential equations to describe the system dynamics is collated. Based on these equations, sensitivity analysis calculations are used to approximately model the nature and the sources of output uncertainty during system operation. These calculations represent a robustness evaluation of the current hearing aid design and offer a means of identifying potential for improved designs of multiphysics systems by way of key parameter identification
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Sensitivity analysis modelling for microscale multiphysics robust engineering design
Sensitivity Analysis (SA) plays an important role in the development of any practical engineering model. It can help to reveal the sources and mechanisms of variability that provide the key to understanding system uncertainty. SA can also be used to calibrate simulation models for closer agreement with experimental results. Robust Engineering Design (RED) seeks to exploit such knowledge in the search for design solutions that are optimal in terms of performance in the face of variability.
Microscale and multiphysics problems present challenges to modelling due to their complexity, which puts increased demands on computational methods. For example, in developing a model of a piezoelectric actuator, the process of calibration is prolonged by the number of parameters that are difficult to verify with the physical device.
In the approach presented in this paper, normalised sensitivity coefficients are determined directly and accurately using the governing finite element model formulation, offering an efficient means of identifying parameters that affect the output of the model, leading to increased accuracy and knowledge of system performance in the face of variability
Modeling Agglomeration of Dust Particles in Plasma
The charge on an aggregate immersed in a plasma environment distributes
itself over the aggregate's surface; this can be approximated theoretically by
assuming a multipole distribution. The dipole-dipole (or higher order) charge
interactions between fractal aggregates lead to rotations of the grains as they
interact. Other properties of the dust grains also influence the agglomeration
process, such as the monomer shape (spherical or ellipsoidal) or the presence
of magnetic material. Finally, the plasma and grain properties also determine
the morphology of the resultant aggregates. Porous and fluffy aggregates are
more strongly coupled to the gas, leading to reduced collisional velocities,
and greater collisional cross sections. These factors in turn can determine the
growth rate of the aggregates and evolution of the dust cloud. This paper gives
an overview of the numerical and experimental methods used to study dust
agglomeration at CASPER and highlights some recent results
Definition and composition of motor primitives using latent force models and hidden Markov models
In this work a different probabilistic motor primitive parameterization is proposed using latent force models (LFMs). The sequential composition of different motor primitives is also addressed using hidden Markov models (HMMs) which allows to capture the redundancy over dynamics by using a limited set of hidden primitives. The capability of the proposed model to learn and identify motor primitive occurrences over unseen movement realizations is validated using synthetic and motion capture data
Wavefunction-Independent Relations between the Nucleon Axial-Coupling g_A and the Nucleon Magnetic Moments
We calculate the proton's magnetic moment and its axial-vector
coupling as a function of its Dirac radius using a relativisitic
three-quark model formulated on the light-cone. The relationship between
and is found to be independent of the assumed form of the
light-cone wavefunction. At the physical radius fm, one obtains the
experimental values for both and , and the helicity carried by the
valence and quarks are each reduced by a factor relative
to their non-relativistic values. At large proton radius, and are
given by the usual non-relativistic formulae. At small radius, becomes
equal to the Dirac moment, as demanded by the Drell-Hearn-Gerasimov sum rule.
In addition, as the constituent quark helicities become completely
disoriented and .Comment: 17 pages, RevTeX, 4 uuencoded figures, SLAC-PUB-643
Reef fish carbonate production assessments highlight regional variation in sedimentary significance (article)
This is the final published version.Available from GSA via the DOI in this record.The dataset associated with this article is located in ORE at: https://doi.org/10.24378/exe.485Recent studies show that all marine bony fish produce mud-sized (<63 ”m) carbonate at rates relevant to carbonate sediment budgets, thus adding to the debate about the often enigmatic origins of fine-grained marine carbonates. However, existing production data are geographically and taxonomically limited, and because different fish families are now known to produce different carbonate polymorphsâan issue relevant to predicting their preservation potentialâthese limitations represent an important knowledge gap. Here we present new data from sites in the Western Pacific Ocean, based on an analysis of 45 fish species. Our data show that previously reported production outputs (in terms of rates and family-specific mineralogies) are applicable across different biogeographic regions. On this basis, we model carbonate production for nine coral reef systems around Australia, with production rates averaging 2.1â9.6 g mâ2 yrâ1, and up to 105 g mâ2 yrâ1 at discrete sites with high fish biomass. With projected production rates on lower-latitude reefs up to two-fold higher, these outputs indicate that carbonate production rates by fish can be comparable with other fine-grained carbonate-producing taxa such as codiacean algae. However, carbonates produced by Australian reef fish assemblages are dominated by a highly unstable amorphous polymorph; a marked contrast to Caribbean assemblages in which Mg calcite dominates. These findings highlight important regional differences in the sedimentary relevance and preservation potential of fish carbonates as a function of historical biogeographic processes that have shaped the worldâs marine fish faunas.Salter, Perry, and Wilson were funded through Natural Environment Research Council (NERC) grants NE/K003143/1 and NE/G010617/1. Harborne was funded through NERC fellowship NE/F015704/1 and Australian Research Council (ARC) fellowship DE120102459
Fish as major carbonate mud producers and missing components of the tropical carbonate factory
This a post-print, author-produced version of an article accepted for publication in Proceedings of the National Academy of Sciences of the United States of America. Copyright © 2011 National Academy of Sciences. The definitive version is available at http://www.pnas.org/content/108/10/3865.fullCarbonate mud is a major constituent of recent marine carbonate sediments and of ancient limestones, which contain unique records of changes in ocean chemistry and climate shifts in the geological past. However, the origin of carbonate mud is controversial and often problematic to resolve. Here we show that tropical marine fish produce and excrete various forms of precipitated (nonskeletal) calcium carbonate from their guts (âlowâ and âhighâ Mg-calcite and aragonite), but that very fine-grained (mostly < 2 ÎŒm) high Mg-calcite crystallites (i.e., MgCO3) are their dominant excretory product. Crystallites from fish are morphologically diverse and species-specific, but all are unique relative to previously known biogenic and abiotic sources of carbonate within open marine systems. Using site specific fish biomass and carbonate excretion rate data we estimate that fish produce âŒ6.1 Ă 106 kg CaCO3/year across the Bahamian archipelago, all as mud-grade (the < 63 ÎŒm fraction) carbonate and thus as a potential sediment constituent. Estimated contributions from fish to total carbonate mud production average âŒ14% overall, and exceed 70% in specific habitats. Critically, we also document the widespread presence of these distinctive fish-derived carbonates in the finest sediment fractions from all habitat types in the Bahamas, demonstrating that these carbonates have direct relevance to contemporary carbonate sediment budgets. Fish thus represent a hitherto unrecognized but significant source of fine-grained carbonate sediment, the discovery of which has direct application to the conceptual ideas of how marine carbonate factories function both today and in the past
Substitutions in the redox-sensing PAS domain of the NifL regulatory protein define an inter-subunit pathway for redox signal transmission
The Per-ARNT-Sim (PAS) domain is a conserved a/Ă fold present within a plethora of signalling proteins from all kingdoms of life. PAS domains are often dimeric and act as versatile sensory and interaction modules to propagate environmental signals to effector domains. The NifL regulatory protein from Azotobacter vinelandii senses the oxygen status of the cell via an FAD cofactor accommodated within the first of two amino-terminal tandem PAS domains, termed PAS1 and PAS2. The redox signal perceived at PAS1 is relayed to PAS2 resulting in conformational reorganization of NifL and consequent inhibition of NifA activity. We have identified mutations in the cofactor-binding cavity of PAS1 that prevent 'release' of the inhibitory signal upon oxidation of FAD. Substitutions of conserved Ă-sheet residues on the distal surface of the FAD-binding cavity trap PAS1 in the inhibitory signalling state, irrespective of the redox state of the FAD group. In contrast, substitutions within the flanking A'a-helix that comprises part of the dimerization interface of PAS1 prevent transmission of the inhibitory signal. Taken together, these results suggest an inter-subunit pathway for redox signal transmission from PAS1 that propagates from core to the surface in a conformation-dependent manner requiring a flexible dimer interface
Revisiting protein aggregation as pathogenic in sporadic Parkinson and Alzheimer diseases.
The gold standard for a definitive diagnosis of Parkinson disease (PD) is the pathologic finding of aggregated α-synuclein into Lewy bodies and for Alzheimer disease (AD) aggregated amyloid into plaques and hyperphosphorylated tau into tangles. Implicit in this clinicopathologic-based nosology is the assumption that pathologic protein aggregation at autopsy reflects pathogenesis at disease onset. While these aggregates may in exceptional cases be on a causal pathway in humans (e.g., aggregated α-synuclein in SNCA gene multiplication or aggregated ÎČ-amyloid in APP mutations), their near universality at postmortem in sporadic PD and AD suggests they may alternatively represent common outcomes from upstream mechanisms or compensatory responses to cellular stress in order to delay cell death. These 3 conceptual frameworks of protein aggregation (pathogenic, epiphenomenon, protective) are difficult to resolve because of the inability to probe brain tissue in real time. Whereas animal models, in which neither PD nor AD occur in natural states, consistently support a pathogenic role of protein aggregation, indirect evidence from human studies does not. We hypothesize that (1) current biomarkers of protein aggregates may be relevant to common pathology but not to subgroup pathogenesis and (2) disease-modifying treatments targeting oligomers or fibrils might be futile or deleterious because these proteins are epiphenomena or protective in the human brain under molecular stress. Future precision medicine efforts for molecular targeting of neurodegenerative diseases may require analyses not anchored on current clinicopathologic criteria but instead on biological signals generated from large deeply phenotyped aging populations or from smaller but well-defined genetic-molecular cohorts
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