276 research outputs found
Beat-to-beat variability of aortic pulse wave velocity:Implications for aortic stiffness measurements
Full text linkObjectives: Aortic pulse wave velocity (aPWV) predicts cardiovascular risk. Being the reference method for aortic stiffness evaluation, invasive aPWV is also recommended for validation of noninvasive devices. Because of intrinsic haemodynamic variability and processing issues, aPWV shows beat-to-beat variability. We aimed to quantify this variability and evaluate its implications for the reliability and use of aPWV as reference in validation and clinical application studies. Methods: The study included n = 84 patients, in whom two datasets of invasive data were recorded: 1) simultaneous ascending aorta and iliac pressure acquisitions using a dual-tip intra-aortic catheter, and 2) an additional ascending aorta pressure acquisition. By combining the iliac and ascending aorta pressure recordings from the first and second acquisitions, respectively, we evaluated how a sequential acquisition protocol affects variability. We compared three pressure waveform foot identification methods to investigate the effect of data processing on variability. Furthermore, we estimated how averaging over n beats consecutive heartbeats affects the standard deviation (SD) of such n beats-averaged estimate of aPWV. Results: The simultaneously acquired invasive aPWV showed a 5% beat-to-beat SD (variability), with small but significant differences between foot identification methods. The sequential acquisition protocol doubled aPWV variability compared to simultaneous acquisition. However, because averaging had a much stronger effect on sequentially measured aPWV, the two acquisition protocols yielded comparable variabilities at n beats = 10 (2% vs. 3%). Conclusions: Our study suggests that, independently from the acquisition protocol and data processing, the intrinsic beat-to-beat variability of aPWV becomes manageable when aPWV values of at least ten heartbeats are averaged
Accepting Optimally in Automated Negotiation with Incomplete Information (abstract)
No full textIntelligent SystemsElectrical Engineering, Mathematics and Computer Scienc
Constitutive interpretation of arterial stiffness in clinical studies:a methodological review
No full textClinical assessment of arterial stiffness relies on noninvasive measurements of regional pulse wave velocity or local distensibility. However, arterial stiffness measures do not discriminate underlying changes in arterial wall constituent properties (e.g., in collagen, elastin, or smooth muscle), which is highly relevant for development and monitoring of treatment. In ARTERIAL STIFFNESS IN RECENT CLINICAL-EPIDEMIOLOGICAL STUDIES, we systematically review clinical-epidemiological studies (2012-) that interpreted arterial stiffness changes in terms of changes in arterial wall constituent properties (63 studies included of 514 studies found). Most studies that did so were association studies (52 of 63 studies) providing limited causal evidence. Intervention studies (11 of 63 studies) addressed changes in arterial stiffness through the modulation of extracellular matrix integrity (5 of 11 studies) or smooth muscle tone (6 of 11 studies). A handful of studies (3 of 63 studies) used mathematical modeling to discriminate between extracellular matrix components. Overall, there exists a notable gap in the mechanistic interpretation of stiffness findings. In CONSTITUTIVE MODEL-BASED INTERPRETATION, we first introduce constitutive-based modeling and use it to illustrate the relationship between constituent properties and stiffness measurements ("forward" approach). We then review all literature on modeling approaches for the constitutive interpretation of clinical arterial stiffness data ("inverse" approach), which are aimed at estimation of constitutive properties from arterial stiffness measurements to benefit treatment development and monitoring. Importantly, any modeling approach requires a tradeoff between model complexity and measurable data. Therefore, the feasibility of changing in vivo the biaxial mechanics and/or vascular smooth muscle tone should be explored. The effectiveness of modeling approaches should be confirmed using uncertainty quantification and sensitivity analysis. Taken together, constitutive modeling can significantly improve clinical interpretation of arterial stiffness findings.</p
Acceptance conditions in automated negotiation
No full textIn every negotiation with a deadline, one of the negotiating parties has to accept an offer to avoid a break off. A break off is usually an undesirable outcome for both parties, therefore it is important that a negotiator employs a proficient mechanism to decide under which conditions to accept. When designing such conditions one is faced with the acceptance dilemma: accepting the current offer may be suboptimal, as better offers may still be presented. On the other hand, accepting too late may prevent an agreement from being reached, resulting in a break off with no gain for either party. Motivated by the challenges of bilateral negotiations between automated agents and by the results and insights of the automated negotiating agents competition (ANAC), we classify and compare state-of-the-art generic acceptance conditions. We focus on decoupled acceptance conditions, i.e. conditions that do not depend on the bidding strategy that is used. We performed extensive experiments to compare the performance of acceptance conditions in combination with a broad range of bidding strategies and negotiation domains. Furthermore we propose new acceptance conditions and we demonstrate that they outperform the other conditions that we study. In particular, it is shown that they outperform the standard acceptance condition of comparing the current offer with the offer the agent is ready to send out. We also provide insight in to why some conditions work better than others and investigate correlations between the properties of the negotiation environment and the efficacy of acceptance conditions.MediamaticsElectrical Engineering, Mathematics and Computer Scienc
Altering Mechanical Properties to Improve Electrode Contacts by Organic Modification of Silica‐Based Ionogel Electrolytes for Sodium‐Ion Batteries
No full textThe author(s) would like to thank Johan Soogen and Koen Daniels for manufacturing the Teflon molds, Ude D. Hangen and Sergey Lemeshko from Bruker for nanoindentation tests, and Koen Van Vinckenroye for technical support. This research was made possible by the Research Foundation Flanders (FWO, project G053519N and 1S08921N) and the Special Research Fund (BOF) of Hasselt University (BOF20INCENT19). This work was further supported by Hasselt University and FWO Vlaanderen via the Hercules project AUHL/15/2 - GOH3816N
Arterial stiffness index beta and cardio-ankle vascular index inherently depend on blood pressure but can be readily corrected
Full text linkObjectives: Arterial stiffness index beta and cardio-ankle vascular index (CAVI) are widely accepted to quantify the intrinsic exponent (beta(0)) of the blood pressure (BP)-diameter relationship. CAVI and b assume an exponential relationship between pressure (P) and diameter (d). We aim to demonstrate that, under this assumption, beta and CAVI as currently implemented are inherently BP-dependent and to provide corrected, BP-independent forms of CAVI and beta. Methods and results: In P = P(ref)e(beta 0[(d/dref)-1)], usually reference pressure (P-ref) and reference diameter (d(ref)) are substituted with DBP and diastolic diameter to accommodate measurements. Consequently, the resulting exponent is not equal to the pressure-independent beta(0). CAVI does not only suffer from this 'reference pressure' effect, but also from the linear approximation of (dP=dd). For example, assuming beta(0) = 7, an increase of SBP/DBP from 110/70 to 170/120mmHg increased beta by 8.1% and CAVI by 14.3%. We derived corrected forms of b and of CAVI (CAVI(0)) that indeed did not change with BP and represent the pressure-independent beta(0). To substantiate the BP effect on CAVI in a typical follow-up study, we realistically simulated patients (n = 161) before and following BP-lowering 'treatment' (assuming no follow-up change in intrinsic beta(0) and therefore in actual P-d relationship). Lowering BP from 160 +/- 14/111 +/- 11 to 120 +/- 15/79 +/- 11 mmHg (p <0.001) resulted in a significant CAVI decrease (from 8.1 +/- 2.0 to 7.7 +/- 2.1, p = 0.008); CAVI(0) did not change (9.8 +/- 2.4 and 9.9 +/- 2.6, p = 0.499). Conclusion: beta and CAVI as currently implemented are inherently BP-dependent, potentially leading to erroneous conclusions in arterial stiffness trials. BP-independent forms are presented to readily overcome this problem
A method for three-dimensional quantification of vascular smooth muscle orientation: application in viable murine carotid arteries
No full textWhen studying in vivo arterial mechanical behaviour using constitutive models, smooth muscle cells (SMCs) should be considered, while they play an important role in regulating arterial vessel tone. Current constitutive models assume a strictly circumferential SMC orientation, without any dispersion. We hypothesised that SMC orientation would show considerable dispersion in three dimensions and that helical dispersion would be greater than transversal dispersion. To test these hypotheses, we developed a method to quantify the 3D orientation of arterial SMCs. Fluorescently labelled SMC nuclei of left and right carotid arteries of ten mice were imaged using two-photon laser scanning microscopy. Arteries were imaged at a range of luminal pressures. 3D image processing was used to identify individual nuclei and their orientations. SMCs showed to be arranged in two distinct layers. Orientations were quantified by fitting a Bingham distribution to the observed orientations. As hypothesised, orientation dispersion was much larger helically than transversally. With increasing luminal pressure, transversal dispersion decreased significantly, whereas helical dispersion remained unaltered. Additionally, SMC orientations showed a statistically significant () mean right-handed helix angle in both left and right arteries and in both layers, which is a relevant finding from a developmental biology perspective. In conclusion, vascular SMC orientation (1) can be quantified in 3D; (2) shows considerable dispersion, predominantly in the helical direction; and (3) has a distinct right-handed helical component in both left and right carotid arteries. The obtained quantitative distribution data are instrumental for constitutive modelling of the artery wall and illustrate the merit of our method
Temperature dependence of the spectral line-width of charge-transfer state emission in organic solar cells; static vs. dynamic disorder
No full textThe origin of energetic disorder in organic semiconductors and its impact on opto-electronic properties remains a topic of intense controversy. Particularly the disorder at electron donor-acceptor interfaces for organic photovoltaics is pivotal to understand as it is expected to affect photo-carrier generation, recombination and consequently device efficiency parameters. In this work we evaluate the temperature dependence of the line-shape of the photoluminescence (PL) and electroluminescence (EL) spectra of small molecule:fullerene blend devices, with the ambition to disentangle dynamic and static disorder contributions. The EL emission spectra are dominated by charge-transfer (CT) state emission and are confirmed to be of Gaussian character and almost completely voltage independent. More importantly, a strong line-width narrowing is persistently observed upon cooling, down to a certain material specific low temperature, below which the line-width remains constant. It is consequently clear that the main portion of the line-width measured at operating conditions of room temperature or higher, is originating from thermally activated, or dynamic, disorder. The observed temperature dependence of the high-energy emission tail can be fully described by taking into account high and low frequency molecular vibrational modes, without having to rely on static disorder. The presence of low frequency molecular modes with large Huang-Rhys factors results in a Gaussian line-shape, which is additionally broadened at high temperature by thermal population of high frequency intra-molecular modes. We therefore cast strong doubts regarding the commonly used assumption that single temperature optical measurements of absorption or emission tails are able to provide meaningful information regarding the shape of a static density of states tail.K. T. acknowledges the German Research Foundation (DFG) through project 382633022 (RECOLPER) and the Experimental Physics VI chair of Prof. Vladimir Dyakonov at Wurzburg University. J. B. acknowledges the DFG project VA 1035/5-1 (Photogen) and the Sachsische Aufbaubank through project no. 100325708 (Infrakart). The authors also acknowledge discussion on the topic with Robert Street, Thomas Kirchartz, Frank Ortmann and Carsten Deibel.Tvingstedt, K (corresponding author), Julius Maximilian Univ Wurzburg, Expt Phys 6, D-97074 Wurzburg, Germany.
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Optimizing the gradient ring of a low-field MRI scanner
No full textThis report describes the study on the optimization of the magnetic field generated by a low-field magnetic resonance imaging modality. In the optimization the Genetic Algorithm and a quasi-Newton Algorithm are used.Low-Field MRIApplied Mathematics | Applied Physic
Cypria ophtalmica Brady & Norman 1889
No full text(7) Cypria ophtalmica (Jurine, 1820) and Cypria lacustris Lilljeborg, 1890: (a) When describing Cypria lacustris, Sars (1890) mentioned that he relied on the description of the species in an unpublished manuscript by Lilljeborg. We here follow Kempf (1980 a–d) who lists the species with Lilljeborg as being the author: Cypria lacustris Lilljeborg, 1890 (in Sars 1890). (b) Cypria lacustris is usually considered an intraspecific form, without a formal taxonomic status of its own, of Cypria ophtalmica because of the occurrence of animals with transitional characters, mainly seen in the number and structure of the female genital processes (Meisch 2000: 217). From the examination, in recent years, of a very large number of individuals belonging to both ‘forms’ from various regions in Europe, one of us (CM) could not confirm the occurrence of ‘transitional’ animals. Furthermore, the ecology differs: Cypria lacustris almost exclusively colonizes springs, waters connected to springs and the profundal zone of lakes, while Cypria ophtalmica occurs in ponds and the littoral zone of lakes. The rare ‘transitional’ individuals recorded in the literature might be the result of very occasional hybridisation between two separate species, though this needs to be confirmed, preferably with molecular methods. In conclusion, Cypria lacustris is listed as a valid species in the present list.Published as part of Meisch, Claude, Smith, Robin J. & Martens, Koen, 2019, A subjective global checklist of the extant non-marine Ostracoda (Crustacea), pp. 1-135 in European Journal of Taxonomy 492 on page 4, DOI: 10.5852/ejt.2019.492, http://zenodo.org/record/327109
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