1,355,298 research outputs found
A Safeguarded Zienkiewicz-Zhu estimator
No full textFor the linear finite element approximation to a linear elliptic model problem, we propose to safeguard the Zienkiewicz-Zhu estimator by an additional estimator for the residual of the averaged gradient. We give a brief account of the theoretical results on reliability, (local) efficiency, and asymptotic exactness of the full estimator and illustrate these properties in numerical tests, incorporating singular solutions and anisotropic ellipticity
Wearable monitoring of central blood pressure using seismocardiography
Full text linkAbstract
Presented thesis aims to advance the field of blood pressure (BP) monitoring by investigating innovative, non-invasive techniques for clinical, research, and wearable applications. BP measurement is essential for cardiovascular health management, yet despite its long history as a clinical standard, the development of continuous, reliable, and unobtrusive BP monitoring remains a significant challenge. The aim of this study is to explore the potential of seismocardiography (SCG), a technique that detects chest vibrations induced by cardiac activity, as an effective method for BP estimation. Additionally, the research investigates how peripheral circulation influences BP measurement and emphasizes the need to account for these factors in BP monitoring systems.
The in vivo datasets used in this research include one collected from subjects performing various physiological tasks and another derived from data recorded during a highly invasive clinical procedure under deep anesthesia. Both datasets feature rapid changes in heart rate, BP, and cardiac output, and include reference BP measurements to assess the accuracy of the BP estimations. In addition to human subject data, the study employs a circulatory system phantom to investigate how vascular properties affect BP estimation in wave propagation-based methods. The phantom model allows for precise manipulation of pulsation rate and pressure, enabling detailed examination of how factors such as vessel elasticity, diameter, and blood viscosity influence signal characteristics and the accuracy of BP estimation. Furthermore, the study explores the potential applications of the method in assessing cerebral autoregulation and sleep studies, expanding the scope of its utility. This work represents the first comprehensive exploration of SCG for continuous BP monitoring, providing valuable insights into its potential as a reliable noninvasive tool for BP monitoring, and for assessing cardiovascular health. Original papers Zienkiewicz, A., Favre, M., Ferdinando, H., Iring, S., Serrador, J., & Myllylä, T. (2021). Blood pressure wave propagation—A multisensor setup for cerebral autoregulation studies. Physiological Measurement, 42(11), 115007. https://doi.org/10.1088/1361-6579/ac3629 https://doi.org/10.1088/1361-6579/ac3629 Self-archived version Zienkiewicz, A., Vihriala, E., Seppala, E., Ferdinando, H., & Myllyla, T. (2022). Wearable sensor system on chest for continuous measurement of blood pressure and other vital signs. 2022 IEEE 16th International Symposium on Medical Information and Communication Technology (ISMICT), 1–6. https://doi.org/10.1109/ISMICT56646.2022.9828307 https://doi.org/10.1109/ISMICT56646.2022.9828307 Zienkiewicz, A., Vihriälä, E., & Myllylä, T. (2024). Influence of arterial vessel diameter and blood viscosity on ptt in pulsatile flow model. In M. Särestöniemi, P. Keikhosrokiani, D. Singh, E. Harjula, A. Tiulpin, M. Jansson, M. Isomursu, M. Van Gils, S. Saarakkala, & J. Reponen (Eds.), Digital Health and Wireless Solutions (Vol. 2084, pp. 186–199). Springer Nature Switzerland. https://doi.org/10.1007/978-3-031-59091-7_13 https://doi.org/10.1007/978-3-031-59091-7_13 Self-archived version Zienkiewicz, A., Korhonen, V., Kiviniemi, V., & Myllylä, T. (2024). Continuous estimation of blood pressure by utilizing seismocardiogram signal features in relation to electrocardiogram. Biosensors, 14(12), 621. https://doi.org/10.3390/bios14120621 https://doi.org/10.3390/bios14120621 Self-archived version Tiivistelmä
Tämä väitöskirja pyrkii edistämään verenpaineen mittausmenetelmiä tutkimalla innovatiivisia, ei-invasiivisia tekniikoita kliinisiin, tutkimus- ja puettaviin sovelluksiin. Verenpaineen mittaaminen on keskeistä sydän- ja verisuoniterveyden hallinnassa, mutta huolimatta sen pitkästä historiasta kliinisenä standardina, jatkuvan, luotettavan ja huomaamattoman verenpaineen seurannan kehittäminen on edelleen merkittävä haaste. Tämän tutkimuksen tavoitteena on tutkia seismokardiografian potentiaalia, tekniikkaa, joka havaitsee sydämen toiminnasta johtuvat rintakehän värähtelyt, menetelmänä verenpaineen arvioimiseksi. Lisäksi tutkimus tarkastelee, kuinka perifeerinen verenkierto vaikuttaa verenpaineen mittaamiseen ja korostaa näiden tekijöiden huomioon ottamisen tarvetta verenpaineen seurantajärjestelmissä.
Tutkimuksessa käytetyt aineistot kattavat mittauksia koehenkilöiltä heidän suorittaessa erilaisia fysiologisia tehtäviä, sekä potilasmittauksia invasiivisen kliinisen toimenpiteen aikana syvässä anestesiassa. Molemmat aineistot sisältävät nopeita muutoksia sykkeen, verenpaineen ja sydämen minuutti-tilavuuden osalta, ja niihin sisältyy vertailuarvot verenpaineen arvioiden tarkkuuden arvioimiseksi. In vivo aineiston lisäksi tutkimuksessa käytetään verisuoniston mallinnusta, jonka avulla voitiin tutkia kuinka verisuonten ominaisuudet vaikuttavat verenpaineen arviointiin verenpaineaaltojen etenemiseen perustuvissa menetelmissä. Malli mahdollistaa pulssinopeuden ja paineen tarkan manipulaation, mikä mahdollistaa verisuonten elastisuuden, läpimitan ja veren viskositeetin vaikutusten yksityiskohtaisen tarkastelun signaalin ominaisuuksiin ja verenpaineen arvioinnin tarkkuuteen. Lisäksi tutkimuksessa arvioidaan menetelmän mahdollisia sovelluksia aivoverenkierron autoregulaation tutkimuksessa ja unitutkimuksissa, laajentaen sen käyttömahdollisuuksia. Tämä työ edustaa ensimmäistä kattavaa seismokardiografian tutkimusta jatkuvassa verenpaineen seurannassa, tarjoten näkemyksiä sen potentiaalista luotettavana, ei-invasiivisena työkaluna verenpaineen mittaamiseksi, sekä sydän- ja verisuoniterveyden seurantaan. Osajulkaisut Zienkiewicz, A., Favre, M., Ferdinando, H., Iring, S., Serrador, J., & Myllylä, T. (2021). Blood pressure wave propagation—A multisensor setup for cerebral autoregulation studies. Physiological Measurement, 42(11), 115007. https://doi.org/10.1088/1361-6579/ac3629 https://doi.org/10.1088/1361-6579/ac3629 Rinnakkaistallennettu versio Zienkiewicz, A., Vihriala, E., Seppala, E., Ferdinando, H., & Myllyla, T. (2022). Wearable sensor system on chest for continuous measurement of blood pressure and other vital signs. 2022 IEEE 16th International Symposium on Medical Information and Communication Technology (ISMICT), 1–6. https://doi.org/10.1109/ISMICT56646.2022.9828307 https://doi.org/10.1109/ISMICT56646.2022.9828307 Zienkiewicz, A., Vihriälä, E., & Myllylä, T. (2024). Influence of arterial vessel diameter and blood viscosity on ptt in pulsatile flow model. In M. Särestöniemi, P. Keikhosrokiani, D. Singh, E. Harjula, A. Tiulpin, M. Jansson, M. Isomursu, M. Van Gils, S. Saarakkala, & J. Reponen (Eds.), Digital Health and Wireless Solutions (Vol. 2084, pp. 186–199). Springer Nature Switzerland. https://doi.org/10.1007/978-3-031-59091-7_13 https://doi.org/10.1007/978-3-031-59091-7_13 Rinnakkaistallennettu versio Zienkiewicz, A., Korhonen, V., Kiviniemi, V., & Myllylä, T. (2024). Continuous estimation of blood pressure by utilizing seismocardiogram signal features in relation to electrocardiogram. Biosensors, 14(12), 621. https://doi.org/10.3390/bios14120621 https://doi.org/10.3390/bios14120621 Rinnakkaistallennettu versio Academic dissertation to be presented with the assent of the Doctoral Programme Committee of Information Technology and Electrical Engineering of the University of Oulu for public defence in the OP auditorium (L10), Linnanmaa, on 14 November 2025, at 12 noonAbstract
Presented thesis aims to advance the field of blood pressure (BP) monitoring by investigating innovative, non-invasive techniques for clinical, research, and wearable applications. BP measurement is essential for cardiovascular health management, yet despite its long history as a clinical standard, the development of continuous, reliable, and unobtrusive BP monitoring remains a significant challenge. The aim of this study is to explore the potential of seismocardiography (SCG), a technique that detects chest vibrations induced by cardiac activity, as an effective method for BP estimation. Additionally, the research investigates how peripheral circulation influences BP measurement and emphasizes the need to account for these factors in BP monitoring systems.
The in vivo datasets used in this research include one collected from subjects performing various physiological tasks and another derived from data recorded during a highly invasive clinical procedure under deep anesthesia. Both datasets feature rapid changes in heart rate, BP, and cardiac output, and include reference BP measurements to assess the accuracy of the BP estimations. In addition to human subject data, the study employs a circulatory system phantom to investigate how vascular properties affect BP estimation in wave propagation-based methods. The phantom model allows for precise manipulation of pulsation rate and pressure, enabling detailed examination of how factors such as vessel elasticity, diameter, and blood viscosity influence signal characteristics and the accuracy of BP estimation. Furthermore, the study explores the potential applications of the method in assessing cerebral autoregulation and sleep studies, expanding the scope of its utility. This work represents the first comprehensive exploration of SCG for continuous BP monitoring, providing valuable insights into its potential as a reliable noninvasive tool for BP monitoring, and for assessing cardiovascular health.Tiivistelmä
Tämä väitöskirja pyrkii edistämään verenpaineen mittausmenetelmiä tutkimalla innovatiivisia, ei-invasiivisia tekniikoita kliinisiin, tutkimus- ja puettaviin sovelluksiin. Verenpaineen mittaaminen on keskeistä sydän- ja verisuoniterveyden hallinnassa, mutta huolimatta sen pitkästä historiasta kliinisenä standardina, jatkuvan, luotettavan ja huomaamattoman verenpaineen seurannan kehittäminen on edelleen merkittävä haaste. Tämän tutkimuksen tavoitteena on tutkia seismokardiografian potentiaalia, tekniikkaa, joka havaitsee sydämen toiminnasta johtuvat rintakehän värähtelyt, menetelmänä verenpaineen arvioimiseksi. Lisäksi tutkimus tarkastelee, kuinka perifeerinen verenkierto vaikuttaa verenpaineen mittaamiseen ja korostaa näiden tekijöiden huomioon ottamisen tarvetta verenpaineen seurantajärjestelmissä.
Tutkimuksessa käytetyt aineistot kattavat mittauksia koehenkilöiltä heidän suorittaessa erilaisia fysiologisia tehtäviä, sekä potilasmittauksia invasiivisen kliinisen toimenpiteen aikana syvässä anestesiassa. Molemmat aineistot sisältävät nopeita muutoksia sykkeen, verenpaineen ja sydämen minuutti-tilavuuden osalta, ja niihin sisältyy vertailuarvot verenpaineen arvioiden tarkkuuden arvioimiseksi. In vivo aineiston lisäksi tutkimuksessa käytetään verisuoniston mallinnusta, jonka avulla voitiin tutkia kuinka verisuonten ominaisuudet vaikuttavat verenpaineen arviointiin verenpaineaaltojen etenemiseen perustuvissa menetelmissä. Malli mahdollistaa pulssinopeuden ja paineen tarkan manipulaation, mikä mahdollistaa verisuonten elastisuuden, läpimitan ja veren viskositeetin vaikutusten yksityiskohtaisen tarkastelun signaalin ominaisuuksiin ja verenpaineen arvioinnin tarkkuuteen. Lisäksi tutkimuksessa arvioidaan menetelmän mahdollisia sovelluksia aivoverenkierron autoregulaation tutkimuksessa ja unitutkimuksissa, laajentaen sen käyttömahdollisuuksia. Tämä työ edustaa ensimmäistä kattavaa seismokardiografian tutkimusta jatkuvassa verenpaineen seurannassa, tarjoten näkemyksiä sen potentiaalista luotettavana, ei-invasiivisena työkaluna verenpaineen mittaamiseksi, sekä sydän- ja verisuoniterveyden seurantaan
Large strain static and dynamic semisaturated soil behaviour
No full textThe theoretical and computational aspects of large strain static and dynamic partially saturated soil analysis are presented. The soil is assumed to be a three-phase material with a solid phase which may yield according to a generalized plasticity theory, whose liquid phase flows according to Darcy's law and where gaseous phase remains equal to the external ambient pressure. Permeability varies not only as a function of the degree of water saturation, but also as a function of the void ratio. These aspects are shown on several examples
Professor Olgierd Cecil Zienkiewicz – a distinguished engineer
No full textThe article discusses both private and professional life of prof. Olgierd Cecil Zienkiewicz who spent most of his life in England. He was a distinguished engineer, specialising in
designing and building huge architectural constructions. What brought him international recognition, however, was his creation of Finite Elements Method, which found its practical use. The method enables the simulation of a design issue in the computer memory without the necessity to build an actual prototype, which greatly facilitates the design process
Leadership emergence in a data-driven model of zebrafish shoals with speed modulation
Full text linkModels of collective animal motion can greatly aid in the design and interpretation of behavioural experiments that seek to unravel, isolate, and manipulate the determinants of leader-follower relationships. Here, we develop an initial model of zebrafish social behaviour, which accounts for both speed and angular velocity regulatory interactions among conspecifics. Using this model, we analyse the macroscopic observables of small shoals influenced by an 'informed' agent, showing that leaders which actively modulate their speed with respect to their neighbours can entrain and stabilise collective dynamics of the naive shoal
The finite element method in the 1990’s A Book Dedicated to O.C. Zienkiewicz
No full textEdited on the occasion of Prof. Olgierd C. Zienkiewicz' 70th birthday, this book contains original contributions from eminent scientists dealing with a wide range of theoretical aspects of the Finite Element Method and its application to a variety of engineering problems. The book provides an overview of the state-of-the-art of finite element technology in the last decade of the 20th centur
Exact integration for singular Zienkiewicz and Guzmán–Neilan finite elements with implementation
No full textDiening L, Storn J, Tscherpel T. Exact integration for singular Zienkiewicz and Guzmán–Neilan finite elements with implementation. Computers & Mathematics with Applications. 2025;191:60-85.We develop a recursive integration formula for a class of rational polynomials in 2D. Based on this, we present implementations of finite elements that have rational basis functions. Specifically, we provide simple MATLAB implementations of the singular Zienkiewicz and the lowest-order Guzmán–Neilan finite element in 2D
Sphingolipid-Induced Programmed Cell Death is a Salicylic Acid and EDS1-Dependent Phenotype in Arabidopsis fatty acid hydroxylase (fah1, fah2) and ceramide synthase (loh2) Triple Mutants
No full textAbstract Ceramides and long chain bases (LCBs) are plant sphingolipids involved in the induction of plant programmed cell death (PCD). The fatty acid hydroxylase mutant fah1 fah2 exhibits high ceramide levels and moderately elevated LCB levels. Salicylic acid glucoside (SAG) level is increased in this mutant, but no cell death can be detected by trypan blue staining. To determine the effect of ceramides with different chain lengths, fah1 fah2 was crossed with ceramide synthase mutants longevity assurance gene one homologue1-3 (loh1, loh2 and loh3). Surprisingly, only triple mutants with loh2 show cell death detected by trypan blue staining under the selected conditions. Sphingolipid profiling revealed that the greatest differences between the triple mutant plants are in the LCB and LCB-phosphate (LCB-P) fraction. fah1 fah2 loh2 plants accumulate LCB d18:0, LCB t18:0and LCB-P d18:0. Crossing fah1 fah2 loh2 with the SA synthesis mutant sid2-2, and with the SA signaling mutants enhanced disease susceptibility 1-2 (eds1-2) and phytoalexin deficient 4-1 (pad4-1), revealed that lesions are SA- and EDS1-dependent. These quadruple mutants also confirm that there may be a feedback loop between SA and sphingolipid metabolism as they accumulated less ceramides and LCBs. In conclusion, PCD in fah1 fah2 loh2 is a SA and EDS1-dependent phenotype, which is likely due to accumulation of LCBs.Abstract Ceramides and long chain bases (LCBs) are plant sphingolipids involved in the induction of plant programmed cell death (PCD). The fatty acid hydroxylase mutant fah1 fah2 exhibits high ceramide levels and moderately elevated LCB levels. Salicylic acid glucoside (SAG) level is increased in this mutant, but no cell death can be detected by trypan blue staining. To determine the effect of ceramides with different chain lengths, fah1 fah2 was crossed with ceramide synthase mutants longevity assurance gene one homologue1-3 (loh1, loh2 and loh3). Surprisingly, only triple mutants with loh2 show cell death detected by trypan blue staining under the selected conditions. Sphingolipid profiling revealed that the greatest differences between the triple mutant plants are in the LCB and LCB-phosphate (LCB-P) fraction. fah1 fah2 loh2 plants accumulate LCB d18:0, LCB t18:0and LCB-P d18:0. Crossing fah1 fah2 loh2 with the SA synthesis mutant sid2-2, and with the SA signaling mutants enhanced disease susceptibility 1-2 (eds1-2) and phytoalexin deficient 4-1 (pad4-1), revealed that lesions are SA- and EDS1-dependent. These quadruple mutants also confirm that there may be a feedback loop between SA and sphingolipid metabolism as they accumulated less ceramides and LCBs. In conclusion, PCD in fah1 fah2 loh2 is a SA and EDS1-dependent phenotype, which is likely due to accumulation of LCBs
Computational geomechanics: The heritage of Olek Zienkiewicz
No full textGeotechnical engineering design is based on mathematical, constitutive and numerical models implemented in computer codes which are able to predict the behaviour of geostructures and foundations under a wide variety of loading conditions, sometimes demanding or extreme. Prediction is fundamental in areas such as seismic engineering, marine foundations or landslide hazard analysis. No computer code is better than the mathematical, constitutive and numerical models which it implements. This paper is devoted to (i) reviewing the decisive contributions of Professor Olek Zienkiewicz to the development of mathematical, constitutive and numerical models in geotechnical engineering and (ii) presenting some extensions based on his work which have been proposed by the authors. The extensions to be described here are the following: (i) a particularization of the u - p(w) Zienkiewicz model to the case of fast catastrophic landslides (ii) an extension of the generalized plasticity model proposed by him and (iii) an SPH numerical model for the propagation of fast catastrophic landslides. Copyright (C) 2011 John Wiley & Sons, Ltd
Elastoplastic soil constitutive laws generalized to partially saturated states
No full textThis paper deals with the plastic behaviour of partially saturated soils by modifying an existing model for fully saturated soils. The saturated
soil model, formulated in the framework of generalized plasticity, considers volumetric as well as deviatoric strain hardening and takes
account of the memory of past stress history and possible limit states. The generalization of the existing model to simulate the experimentally observed behaviour of partially saturated soils has been obtained by introducing Bishop's stress and suction as independent stress parameters and by modifying the hardening parameter and the yield condition to take into account the role of suction
- …
