292 research outputs found
Mode Selection for Component Mode Synthesis with Guaranteed Assembly Accuracy
In this work, a modular approach is introduced to select the most important
eigenmodes for each component of a composed structural dynamics system to
obtain the required accuracy of the reduced-order assembly model. To enable the
use of models of complex (structural) dynamical systems in engineering
practice, e.g., in a design, optimization and/or control context, the
complexity of the models needs to be reduced. When the model consist of an
assembly of multiple interconnected structural components, component mode
synthesis is often the preferred model reduction method. The standard approach
to component mode synthesis for such system is to select the eigenmodes of a
component that are most important to accurately model the dynamic behavior of
this component in a certain frequency range of interest. However, often, a more
relevant goal is to obtain, in this frequency range, an accurate model of the
assembly. In the proposed approach, accuracy requirements on the level of the
assembly are translated to accuracy requirements on component level, by
employing techniques from the field of systems and control. With these
component-level requirements, the eigenmodes that are most important to
accurately model the dynamic behavior of the assembly can be selected in a
modular fashion. We demonstrate with two structural dynamics benchmark systems
that this method based on assembly accuracy allows for a computationally
efficient selection of eigenmodes that 1) guarantees satisfaction of the
assembly accuracy requirements and 2) results in most cases in reduced-order
models of significantly lower order with respect to the industrial standard
approach in which component eigenmodes are selected using a frequency
criterion
Translating Assembly Accuracy Requirements to Cut-Off Frequencies for Component Mode Synthesis
One of the most popular methods for reducing the complexity of assemblies of
finite element models in the field of structural dynamics is component mode
synthesis. A main challenge of component mode synthesis is balancing model
complexity and model accuracy, because it is difficult to predict how component
reduction influences assembly model accuracy. This work introduces an approach
that allows for the translation of assembly model accuracy requirements in the
frequency domain to the automatic selection of the cut-off frequencies for the
model-order reduction (MOR) of components. The approach is based on a
mathematical approach for MOR for coupled linear systems in the field of
systems and control. We show how this approach is also applicable to structural
dynamics models. We demonstrate the use of this approach in the scope of
component mode synthesis (CMS) methods with the aim to reduce the complexity of
component models while guaranteeing accuracy requirements of the assembly
model. The proposed approach is illustrated on a mechanical, three-component
structural dynamics system for which reduced-order models are computed that are
reduced further compared to reduction using standard methods. This results in
lower simulation cost, while maintaining the required accuracy
Modular Redesign of Mechatronic Systems: Formulation of Module Specifications Guaranteeing System Dynamics Specifications
Complex mechatronic systems are typically composed of interconnected modules,
often developed by independent teams. This development process challenges the
verification of system specifications before all modules are integrated. To
address this challenge, a modular redesign framework is proposed in this paper.
Herein, first, allowed changes in the dynamics (represented by frequency
response functions (FRFs)) of the redesigned system are defined with respect to
the original system model, which already satisfies system specifications.
Second, these allowed changes in the overall system dynamics (or system
redesign specifications) are automatically translated to dynamics (FRF)
specifications on module level that, when satisfied, guarantee overall system
dynamics (FRF) specifications. This modularity in specification management
supports local analysis and verification of module design changes, enabling
design teams to work in parallel without the need to iteratively rebuild the
system model to check fulfilment of system FRF specifications. A modular
redesign process results that shortens time-to-market and decreases redesign
costs. The framework's effectiveness is demonstrated through three examples of
increasing complexity, highlighting its potential to enable modular mechatronic
system (re)design
Can incontinence be cured? A systematic review of cure rates
Background
Incontinence constitutes a major health problem affecting millions of people worldwide. The present study aims to assess cure rates from treating urinary (UI) or fecal incontinence (FI) and the number of people who may remain dependent on containment strategies.
Methods
Medline, Embase, PsycINFO, Cochrane Central Register of Controlled Trials (CENTRAL), CINAHL, and PEDro were searched from January 2005 to June 2015. Supplementary searches included conference abstracts and trials registers (2013–2015). Included studies had patients ≥ 18 years with UI or FI, reported treatment cure or success rates, had ≥ 50 patients treated with any intervention recognized in international guideline algorithms, a follow-up ≥ 3 months, and were published from 2005 onwards. Title and abstract screening, full paper screening, data extraction and risk-of-bias assessment were performed independently by two reviewers. Disagreements were resolved through discussion or referral to a third reviewer where necessary. A narrative summary of included studies is presented.
Results
Most evidence was found for UI: Surgical interventions for stress UI showed a median cure rate of 82.3% (interquartile range (IQR), 72–89.5%); people with urgency UI were mostly treated using medications (median cure rate for antimuscarinics = 49%; IQR, 35.6–58%). Pelvic floor muscle training and bulking agents showed lower cure rates for UI. Sacral neuromodulation for FI had a median cure rate of 38.6% (IQR, 35.6–40.6%).
Conclusions
Many individuals were not cured and hence may continue to rely on containment. No studies were found assessing success of containment strategies. There was a lack of data in the disabled and in those with neurological diseases, in the elderly and those with cognitive impairment. Surgical interventions were effective for stress UI. Other interventions for UI and FI showed lower cure rates. Many individuals are likely to be reliant on containment strategies
Hypertension Is Associated with Marked Alterations in Sphingolipid Biology: A Potential Role for Ceramide
Background
Hypertension is, amongst others, characterized by endothelial dysfunction and vascular remodeling. As sphingolipids have been implicated in both the regulation of vascular contractility and growth, we investigated whether sphingolipid biology is altered in hypertension and whether this is reflected in altered vascular function. Methods and Findings
In isolated carotid arteries from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats, shifting the ceramide/S1P ratio towards ceramide dominance by administration of a sphingosine kinase inhibitor (dimethylsphingosine) or exogenous application of sphingomyelinase, induced marked endothelium-dependent contractions in SHR vessels (DMS: 1.4±0.4 and SMase: 2.1±0.1 mN/mm; n = 10), that were virtually absent in WKY vessels (DMS: 0.0±0.0 and SMase: 0.6±0.1 mN/mm; n = 9, p Conclusions
Hypertension is associated with marked alterations in vascular sphingolipid biology such as elevated ceramide levels and signaling, that contribute to increased vascular tone
Elevated Uptake of Plasma Macromolecules by Regions of Arterial Wall Predisposed to Plaque Instability in a Mouse Model
Atherosclerosis may be triggered by an elevated net transport of lipid-carrying
macromolecules from plasma into the arterial wall. We hypothesised that whether
lesions are of the thin-cap fibroatheroma (TCFA) type or are less fatty and more
fibrous depends on the degree of elevation of transport, with greater uptake leading
to the former. We further hypothesised that the degree of elevation can depend on
haemodynamic wall shear stress characteristics and nitric oxide synthesis. Placing
a tapered cuff around the carotid artery of apolipoprotein E -/- mice modifies
patterns of shear stress and eNOS expression, and triggers lesion development at
the upstream and downstream cuff margins; upstream but not downstream lesions
resemble the TCFA. We measured wall uptake of a macromolecular tracer in the
carotid artery of C57bl/6 mice after cuff placement. Uptake was elevated in the
regions that develop lesions in hyperlipidaemic mice and was significantly more
elevated where plaques of the TCFA type develop. Computational simulations and
effects of reversing the cuff orientation indicated a role for solid as well as fluid
mechanical stresses. Inhibiting NO synthesis abolished the difference in uptake
between the upstream and downstream sites. The data support the hypothesis that
excessively elevated wall uptake of plasma macromolecules initiates the
development of the TCFA, suggest that such uptake can result from solid and fluid
mechanical stresses, and are consistent with a role for NO synthesis. Modification
of wall transport properties might form the basis of novel methods for reducing
plaque rupture
Valid and reliable instruments for arm-hand assessment at ICF activity level in persons with hemiplegia: a systematic review
Contains fulltext :
110141.pdf (publisher's version ) (Open Access)BACKGROUND: Loss of arm-hand performance due to a hemiparesis as a result of stroke or cerebral palsy (CP), leads to large problems in daily life of these patients. Assessment of arm-hand performance is important in both clinical practice and research. To gain more insight in e.g. effectiveness of common therapies for different patient populations with similar clinical characteristics, consensus regarding the choice and use of outcome measures is paramount. To guide this choice, an overview of available instruments is necessary. The aim of this systematic review is to identify, evaluate and categorize instruments, reported to be valid and reliable, assessing arm-hand performance at the ICF activity level in patients with stroke or cerebral palsy. METHODS: A systematic literature search was performed to identify articles containing instruments assessing arm-hand skilled performance in patients with stroke or cerebral palsy. Instruments were identified and divided into the categories capacity, perceived performance and actual performance. A second search was performed to obtain information on their content and psychometrics. RESULTS: Regarding capacity, perceived performance and actual performance, 18, 9 and 3 instruments were included respectively. Only 3 of all included instruments were used and tested in both patient populations. The content of the instruments differed widely regarding the ICF levels measured, assessment of the amount of use versus the quality of use, the inclusion of unimanual and/or bimanual tasks and the inclusion of basic and/or extended tasks. CONCLUSIONS: Although many instruments assess capacity and perceived performance, a dearth exists of instruments assessing actual performance. In addition, instruments appropriate for more than one patient population are sparse. For actual performance, new instruments have to be developed, with specific focus on the usability in different patient populations and the assessment of quality of use as well as amount of use. Also, consensus about the choice and use of instruments within and across populations is needed
American Gut: an Open Platform for Citizen Science Microbiome Research
McDonald D, Hyde E, Debelius JW, et al. American Gut: an Open Platform for Citizen Science Microbiome Research. mSystems. 2018;3(3):e00031-18
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