Academic literature on the topic 'Biological artificial valve'
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Journal articles on the topic "Biological artificial valve"
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Kowalska, Wiktoria, Ewa Jędrzejczyk-Patej, Aleksandra Konieczny, Jonasz Kozielski, Maciej Bugajski, Aleksandra Woźniak, Oskar Kowalski, and Beata Średniawa. "Medtronic Micra leadless pacemaker implantation to patient with artificial tricuspid valve." In a good rythm 4, no. 45 (December 29, 2017): 16–19. http://dx.doi.org/10.5604/01.3001.0010.7492.
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In case of the need of pacemaker implantation, patients with artificial tricuspid valve are a special group of subjects, because of high risk of dysfunction of the prosthesis. In case of mechanical prosthesis of tricuspid valve the leads of pacemaker are usually located in coronary sinus. In case of biological prosthesis of tricuspid valve despite of the risk of prosthesis damage the electrodes are implanted endocardially. The leadless pacemakers seems to be promising alternative in patients with artificial tricuspid valve because of minor risk of valve damage. The case report concerns to the patient with tachycardia-bradycardia syndrome and biological prosthesis of tricuspid valve in whom the leadless pacemaker Micra was implanted.
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Askadinov, M. N., B. K. Kadyraliev, S. H. Lilotkhia, O. G. Musaev, and V. B. Arutyunyan. "Aortic valve leaflet replacement using autopericardium as an alternative approach of aortic valve stenosis treatment: literature review." Perm Medical Journal 37, no. 5 (January 7, 2021): 52–60. http://dx.doi.org/10.17816/pmj37552-60.
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Regarding degenerative defects of the aortic valve, the main method of treatment is dissection of malformed leaflets and placement of prosthetic valve. In most cases, mechanical and biological prostheses are used. Each type of prosthesis has shortcomings related to both the implantation technique and essential medication support to keep it functioning. Patients with implanted mechanical prosthesis need lifelong anticoagulation therapy and constant monitoring of blood coagulation rates, where on the one hand there is a risk of occurring thromboembolic complications, and on the other hand haemorrhagic complications. The peculiarity of biological prostheses is a high probability of degeneration and the need for re-operation, especially in young patients, therefore the implantation of such prostheses is mainly carried out in elderly patients. Despite continuous change and modification of artificial valves, the ideal aortic valve prosthesis does not exist today. Various attempts to replace aortic valve leaflets with artificial and biological materials have not succeeded or gained great recognition. In 2007, Shigeyuki Ozaki introduced a technique to replace the aortic valve leaflets with an autopericardium treated with 0.6 % glutar aldehyde solution. Inspite of the encouraging mid-term results, this surgery has not yet become widespread among cardiac surgeons due to the complicated operating technique and lack of long-term results. Considering the research of literature, experience of different cardiosurgical centers in this field as well as our own experience, there is a need to systematize the results of Ozaki procedure, among patients with aortic valve pathology, presented in the recent publications.
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Askadinov, M. N., B. K. Kadyraliev, S. H. Lilotkhia, O. G. Musaev, and V. B. Arutyunyan. "Aortic valve leaflet replacement using autopericardium as an alternative approach of aortic valve stenosis treatment: literature review." Perm Medical Journal 37, no. 5 (January 7, 2021): 52–60. http://dx.doi.org/10.17816/pmj37552-60.
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Regarding degenerative defects of the aortic valve, the main method of treatment is dissection of malformed leaflets and placement of prosthetic valve. In most cases, mechanical and biological prostheses are used. Each type of prosthesis has shortcomings related to both the implantation technique and essential medication support to keep it functioning. Patients with implanted mechanical prosthesis need lifelong anticoagulation therapy and constant monitoring of blood coagulation rates, where on the one hand there is a risk of occurring thromboembolic complications, and on the other hand haemorrhagic complications. The peculiarity of biological prostheses is a high probability of degeneration and the need for re-operation, especially in young patients, therefore the implantation of such prostheses is mainly carried out in elderly patients. Despite continuous change and modification of artificial valves, the ideal aortic valve prosthesis does not exist today. Various attempts to replace aortic valve leaflets with artificial and biological materials have not succeeded or gained great recognition. In 2007, Shigeyuki Ozaki introduced a technique to replace the aortic valve leaflets with an autopericardium treated with 0.6 % glutar aldehyde solution. Inspite of the encouraging mid-term results, this surgery has not yet become widespread among cardiac surgeons due to the complicated operating technique and lack of long-term results. Considering the research of literature, experience of different cardiosurgical centers in this field as well as our own experience, there is a need to systematize the results of Ozaki procedure, among patients with aortic valve pathology, presented in the recent publications.
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Maciejewski, Marek, Katarzyna Piestrzeniewicz, Agata Bielecka-Dabrowa, and Andrzej Walczak. "Biological artificial valve dysfunction – single-centre, observational echocardiographic study in patients operated on before age 65 years." Archives of Medical Science 6 (2011): 993–99. http://dx.doi.org/10.5114/aoms.2011.26611.
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Arbeiter, Daniela, Christoph Brandt-Wunderlich, Stefan Siewert, Stefanie Kohse, Sylvia Pfensig, Klaus-Peter Schmitz, and Niels Grabow. "Cyclic stress-strain behavior of polymeric nonwoven structures for the use as artificial leaflet material for transcatheter heart valve prostheses." Current Directions in Biomedical Engineering 3, no. 2 (September 7, 2017): 703–6. http://dx.doi.org/10.1515/cdbme-2017-0149.
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AbstractXenogenic leaflet material, bovine and porcine pericardium, is widely used for the fabrication of surgically implanted and transcatheter heart valve prostheses. As a biological material, long term durability of pericardium is limited due to calcification, degeneration and homogeneity. Therefore, polymeric materials represent a promising approach for a next generation of artificial heart valve leaflets with improved durability. Within the current study we analyzed the mechanical performance of polymeric structures based on elastomeric materials. Polymeric cast films were prepared and nonwovens were manufactured in an electrospinning process. Analysis of cyclic stress-strain behavior was performed, using a universal testing machine. The uniaxial cyclic tensile experiments of the elastomeric samples yielded a non-linear elastic response due to viscoelastic behavior with hysteresis. Equilibrium of stress-strain curves was found after a specific number of cycles, for cast films and nonwovens, respectively. In conclusion, preconditioning was found obligatory for the evaluation of the mechanical performance of polymeric materials for the use as artificial leaflet material for heart valve prostheses.
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Grams, Samantha Torres, Karen Yumi Mota Kimoto, Elen Moda de Oliveira Azevedo, Marina Lança, André Luis Pereira de Albuquerque, Christina May Moran de Brito, and Wellington Pereira Yamaguti. "Unidirectional Expiratory Valve Method to Assess Maximal Inspiratory Pressure in Individuals without Artificial Airway." PLOS ONE 10, no. 9 (September 11, 2015): e0137825. http://dx.doi.org/10.1371/journal.pone.0137825.
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Vemula, Dheeraj, Jeong Yong Kim, Nicholas Mazzoleni, and Matthew Bryant. "Design, analysis, and validation of an orderly recruitment valve for bio-inspired fluidic artificial muscles." Bioinspiration & Biomimetics 17, no. 2 (January 24, 2022): 026001. http://dx.doi.org/10.1088/1748-3190/ac4381.
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Abstract Biological musculature employs variable recruitment of muscle fibers from smaller to larger units as the load increases. This orderly recruitment strategy has certain physiological advantages like minimizing fatigue and providing finer motor control. Recently fluidic artificial muscles (FAM) are gaining popularity as actuators due to their increased efficiency by employing bio-inspired recruitment strategies such as active variable recruitment (AVR). AVR systems use a multi-valve system (MVS) configuration to selectively recruit individual FAMs depending on the load. However, when using an MVS configuration, an increase in the number of motor units in a bundle corresponds to an increase in the number of valves in the system. This introduces greater complexity and weight. The objective of this paper is to propose, analyze, and demonstrate an orderly recruitment valve (ORV) concept that enables orderly recruitment of multiple FAMs in the system using a single valve. A mathematical model of an ORV-controlled FAM bundle is presented and validated by experiments performed on a proof-of-concept ORV experiment. The modeling is extended to explore a case study of a 1-DOF robot arm system consisting of an electrohydraulic pressurization system, ORV, and a FAM-actuated rotating arm plant and its dynamics are simulated to further demonstrate the capabilities of an ORV-controlled closed-loop system. An orderly recruitment strategy was implemented through a model-based feed forward controller. To benchmark the performance of the ORV, a conventional MVS with equivalent dynamics and controller was also implemented. Trajectory tracking simulations on both the systems revealed lower tracking error for the ORV controlled system compared to the MVS controlled system due to the unique cross-flow effects present in the ORV. However, the MVS, due to its independent and multiple valve setup, proved to be more adaptable for performance. For example, modifications to the recruitment thresholds of the MVS demonstrated improvement in tracking error, albeit with a sacrifice in efficiency. In the ORV, tracking performance remained insensitive to any variation in recruitment threshold. The results show that compared to the MVS, the ORV offers a simpler and more compact valving architecture at the expense of moderate losses in control flexibility and performance.
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Christo, SW, TM Absher, and G. Boehs. "Morphology of the larval shell of three oyster species of the genus Crassostrea Sacco, 1897 (Bivalvia: Ostreidae)." Brazilian Journal of Biology 70, no. 3 (August 2010): 645–50. http://dx.doi.org/10.1590/s1519-69842010000300023.
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In this study we describe the morphology of the larval shell of three oyster species of Crassostrea genus. Two species, C. rhizophorae and C. brasiliana, are native to the Brazilian coast, and C. gigas is an introduced species. Samples of laboratory reared larvae, obtained through artificial fertilisation, were collected at intervals during the cultivation process for analysis using Scanning Electron Microscopy (SEM). Prodissoconch morphology was observed in relation to the presence, position, form and number of teeth in the three larval stages: D-shaped larva, umbo larva and pediveliger. Characteristic of D-shaped larvae of C. rhizophorae was the total absence of teeth in the provinculum area while C. brasiliana and C. gigas had two anterior and two posterior teeth in each valve. In the umbo larval phase, the three species had the same number of teeth in each valve: two posterior and two anterior teeth in the right valve and three posterior and three anterior in the left valve. In the pediveliger stage the three species could be differentiated by the number of anterior teeth of the right valve: C. rhizophorae had two teeth, C. brasiliana one tooth and C. gigas three teeth.
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Schubert, Julia, Kerstin Schümann, Sabine Kischkel, Wolfram Schmidt, Niels Grabow, Michael Stiehm, Sylvia Pfensig, Klaus-Peter Schmitz, Jonas Keiler, and Andreas Wree. "Numerical simulation of the functionality of a stent structure for venous valve prostheses." Current Directions in Biomedical Engineering 5, no. 1 (September 1, 2019): 477–79. http://dx.doi.org/10.1515/cdbme-2019-0120.
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AbstractChronic venous insufficiency (CVI) is a common disease characterized by impaired venous drainage leading to congestion in the lower limbs. Currently, there are no artificial or biological venous valve prostheses commercially available. Previous minimally invasive design concepts failed to achieve sufficient long term results in animal or in vitro studies. The aim was to implement structural numerical simulation of clinically relevant loading cases for minimally invasive implantable venous valve prostheses. A bicuspid valve design was chosen as it showed superior results compared to tricuspid valves in previous studies. The selfexpanding support structure was developed by using diamond-shaped elements. Using finite-element analysis (FEA), various loading cases, including expansion and crimping of the stent structure and the release into a venous vessel, were simulated. A hyperelastic constitutive law for the vascular model was generated from uniaxial tensile test data of unfixated human vein walls. This study also compared numerical and experimental results regarding compliance and tensile tests to validate the vein material model. The calculated performance concerning expansion and crimping, as well as the release of the stent into a venous vessel, demonstrated the suitability of the stent design for minimally invasive application.
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Wilczek, P. "Heart valve bioprothesis; effect of different acellularizations methods on the biomechanical and morphological properties of porcine aortic and pulmonary valve." Bulletin of the Polish Academy of Sciences: Technical Sciences 58, no. 2 (June 1, 2010): 337–42. http://dx.doi.org/10.2478/v10175-010-0032-4.
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Heart valve bioprothesis; effect of different acellularizations methods on the biomechanical and morphological properties of porcine aortic and pulmonary valveTissue engineering is a promising tool for the creation of a new type of the heart valve bioprothesis. The biological scaffold composed of decellularized tissue has been successfully used for the constructions of the valve prosthesis. An analysis of the efficiency of the valve leaflet acellularization methods and the influence of those methods on the morphology and the biomechanical properties of the ECM (extra cellular matrix) was performed. Fresh porcine hearts obtained from a slaughterhouse were used in the experiments. The efficiency of the acellularization methods was dependent on the tissue type and the acellularoization methods used. The more effective were the enzymatic methods, both because of the cell removal efficiency and the effect on the biomechanical properties of the heart valve. The differences in the biomechanical and morphological properties of the porcine aortic and the pulmonary valve after different types of the acellularization process could influence the hemodynamic conditions of the heart after the valve replacement, which limited the range of the tissue types used for the creations of the tissue engineered heart valve.
Dissertations / Theses on the topic "Biological artificial valve"
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Bachlah, Dana Mohamad. "Modeling of the inner structural band of the aortic valve bio prosthesis." Bachelor's thesis, Igor Sikorsky Kyiv Polytechnic Institute, 2021. https://ela.kpi.ua/handle/123456789/43660.
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Обсяг дипломної роботи становить 73 сторінок, містить 28 ілюстрацій, 20 таблиць. Загалом опрацьовано 59 джерел.
Актуальність: Захворювання аортального клапана призводять до серйозних дисфункцій, спричинених зворотним потоком клапана або підвищенням його опору. Наслідком цієї патології є важка серцева недостатність, скорочення тривалості та якість життя. Єдине лікування - хірургічна заміна клапана на штучний протез або пластику аортального клапана. Заміна хворого аортального клапана на штучний протез є ефективним методом профілактики серцевої недостатності, збільшення тривалості та поліпшення якості життя.
Мета: Моделювання внутрішньої структурної смуги біопротезу аортального клапана.
Завдання: переглянути літературу з анатомії судин та клапанів серця; проаналізувати та виявити проблему; побудувати внутрішню структурну клапанну модель клапана у винахіднику AutoCAD; Аналіз варіантів матеріалів для виготовлення клапанного корпусу показав прийнятні механічні характеристики та біосумісність.
Основні результати: переглянуто літературу з суміжних тем; порівняльний аналіз існуючих прототипів штучних клапанів серця; вибір «біологічного нітинолу»; Розроблено 5 стандартних розмірів каркаса для біопротезування аортального клапана.The volume of the graduation work is 73 pages, contains 28 illustrations, 20 tables. In total 59 sources have been processed. Relevance: Aortic valve diseases lead to its severe dysfunction caused backflow on the valve or increased its resistance. The consequence of this pathology is severe heart failure, reduced duration and quality of life. The only treatment is surgical replacement of the valve with an artificial prosthesis or aortic valve plastic. Replacing of a sick aortic valve with an artificial prosthesis is an effective method of preventing heart failure, increasing duration and improving quality of life. Purpose: Modeling of the inner structural band of the aortic valve bio prosthesis. Tasks: to review literature on anatomy of blood vessels and heart valves; analyze and identify the problem; build inner structural band valve model in AutoCAD inventor; analyze the material options for the manufacture of the valve frame showed acceptable mechanical characteristics and biocompatibility. Main results: literature on related topics has been reviewed; comparative analysis of existing prototypes of artificial heart valves; selection of “biological nitinol”; 5 standard sizes of frame for aortic valve bio prosthesis was designed.
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Moffat, Shannon Marija. "Biologically Inspired Legs and Novel Flow Control Valve Toward a New Approach for Accessible Wearable Robotics." Digital WPI, 2019. https://digitalcommons.wpi.edu/etd-theses/1279.
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The Humanoid Walking Robot (HWR) is a research platform for the study of legged and wearable robots actuated with Hydro Muscles. The fluid operated HWR is representative of a class of biologically inspired, and in some aspects highly biomimetic robotic musculoskeletal appendages showing certain advantages in comparison to more conventional artificial limbs and braces for physical therapy/rehabilitation, assistance of daily living, and augmentation. The HWR closely mimics the human body structure and function, including the skeleton, ligaments, tendons, and muscles. The HWR can emulate close to human-like movements even when subjected to simplified control laws. One of the main drawbacks of this approach is the inaccessibility of an appropriate fluid flow management support system, in the form of affordable, lightweight, compact, and good quality valves suitable for robotics applications. To resolve this shortcoming, the Compact Robotic Flow Control Valve (CRFC Valve) is introduced and successfully proof-of-concept tested. The HWR added with the CRFC Valve has potential to be a highly energy efficient, lightweight, controllable, affordable, and customizable solution that can resolve single muscle action.
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Santos, Talles Batista Rattis. "Sistema de triagem de pericárdio bovino para manufatura de válvulas cardíacas por tomografia de impedância elétrica." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/3/3152/tde-07032016-114749/.
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Durante a triagem do pericárdio bovino, utilizado em válvulas cardíacas artificiais, procura-se determinar a direção das fibras de colágeno e identificar regiões mais homogêneas. Estas características influenciam o comportamento mecânico e a durabilidade destas válvulas. Neste contexto, a tomografia de impedância elétrica (TIE) poderia ser utilizada como ferramenta para avaliar o pericárdio, a partir da estimação da direção média das fibras e da identificação das regiões mais homogêneas. O objetivo deste trabalho é investigar a possibilidade de utilização da técnica de TIE para análise e seleção de pericárdios, melhorando os critérios de seleção deste tecido. Com este propósito, foi desenvolvido um reservatório, para acondicionamento do pericárdio e coleta de dados, e implementado um algoritmo de Gauss-Newton para estimar a distribuição de resistividade no tecido. Para regularização do problema inverso mal-posto foi desenvolvido e utilizado um prior baseado em amostras. E para avaliar o desempenho do reservatório e do algoritmo de imagem, fantomas e testes in vitro foram realizados. Detectou-se um furo de 2.0 mm de raio provocado no tecido. Portanto, os experimentos mostraram que é possível detectar imperfeições no pericárdio utilizando a técnica de TIE. No entanto, a necessidade de aperfeiçoamento dos eletrodos, fonte de corrente, reservatório e algoritmo (malhas e priors) esta clara se o objetivo final for a seleção de pericárdios para válvulas cardíaca artificiais.During the selection of bovine pericardium for use in artificial heart valves, one of the goals is to determine the direction of the collagen fibers and to identify more homogeneous regions. These characteristics influence the mechanical behavior and the durability of these valves. In this context, the electrical impedance tomography (EIT) could be employed as a tool to evaluate the pericardium, from the estimation of the mean fiber direction and the identification of homogeneous regions. The objective of this work is to investigate the possibility of using EIT technique for analysis and selection of pericardium, improving the selection criteria of this tissue. With this purpose in mind, it was developed a test bench, to accommodate the pericardium and to collect data, and it was implemented a Gauss-Newton based algorithm to estimate the resistivity distribution map of this tissue. For regularizing this ill-posed problem, it was developed and applied a priormodels sample-based. And for quality evaluation of the test bench and of the image algorithm, phantom experiments and in vitro tests were performed. It was detected a hole of 2.0 mm radius at the tissue. Therefore, the experiments showed that it is possible to detect defects on pericardium using EIT technique. However, the need of improvements on electrodes, current source, test bench and algorithm (meshes and priors) is clear if the final aim is the selection of pericardium for artificial heart valves.
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Maas, Bea. "Birds, bats and arthropods in tropical agroforestry landscapes: Functional diversity, multitrophic interactions and crop yield." Doctoral thesis, 2013. http://hdl.handle.net/11858/00-1735-0000-0022-5E77-5.
Full textBooks on the topic "Biological artificial valve"
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Aortic Root Surgery The Biological Solution. Springer, 2010.
Find full textBook chapters on the topic "Biological artificial valve"
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Obidowski, D., P. Klosinski, P. Reorowicz, and K. Jozwik. "Influence of an Artificial Valve Type on the Flow in the Ventricular Assist Device." In XII Mediterranean Conference on Medical and Biological Engineering and Computing 2010, 410–13. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-13039-7_103.
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Kasderidis, Stathis, and John G. Taylor. "Combining Attention and Value Maps." In Artificial Neural Networks: Biological Inspirations – ICANN 2005, 79–84. Berlin, Heidelberg: Springer Berlin Heidelberg, 2005. http://dx.doi.org/10.1007/11550822_13.
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Wolfsdorf, David Conan. "Value." In On Goodness, 89–137. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780190688509.003.0004.
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The gradable property associated with “good” is value. Chapter 4 pursues the question “What is value?” and does so by linguistic means. The term “value” is a mass noun. This mass noun is polysemous between generic and specific senses; where the former comprises so-called negative, neutral, and positive value; and the latter denotes only positive value. The chapter argues that positive value is purpose serving, which is to say contribution to the realization of a purpose. Consequently, for an entity x to be good is for x to contribute to the realization of a purpose to a significant degree. “Purpose,” as here employed, is a univocal modal term, whose denotation comprises at least four basic kinds: biological and characteristic artificial purposes and ad hoc purposes derived from either intentions or desires. The chapter concludes with a discussion of the relation between value and quality.
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Shulman, Carl, and Nick Bostrom. "Sharing the World with Digital Minds." In Rethinking Moral Status, 306–26. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780192894076.003.0018.
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The minds of biological creatures occupy a small corner of a much larger space of possible minds that could be created once we master the technology of artificial intelligence. Yet many of our moral intuitions and practices are based on assumptions about human nature that need not hold for digital minds. This points to the need for moral reflection as we approach the era of advanced machine intelligence. This chapter focuses on one set of issues, which arise from the prospect of digital minds with superhumanly strong claims to resources and influence. These could arise from the vast collective benefits that mass-produced digital minds could derive from relatively small amounts of resources. Alternatively, they could arise from individual digital minds with superhuman moral status or ability to benefit from resources. Such beings could contribute immense value to the world, and failing to respect their interests could produce a moral catastrophe, while a naive way of respecting them could be disastrous for humanity. A sensible approach requires reforms of our moral norms and institutions along with advance planning regarding what kinds of digital minds we bring into existence.
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Bäck, Thomas. "Organic Evolution and Problem Solving." In Evolutionary Algorithms in Theory and Practice. Oxford University Press, 1996. http://dx.doi.org/10.1093/oso/9780195099713.003.0006.
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Evolutionary Algorithms (EAs), the topic of this work, is an interdisciplinary research field with a relationship to biology, Artificial Intelligence, numerical optimization, and decision support in almost any engineering discipline. Therefore, an attempt to cover at least some of these relations must necessarily result in several introductory pages, always having in mind that it hardly can be complete. This is the reason for a rather voluminous introduction to the fundamentals of Evolutionary Algorithms in section 1.1 without giving any practically useful description of the algorithms now. At the moment, it is sufficient to know that these algorithms are based on models of organic evolution, i.e., nature is the source of inspiration. They model the collective learning process within a population of individuals, each of which represents not only a search point in the space of potential solutions to a given problem, but also may be a temporal container of current knowledge about the “laws” of the environment. The starting population is initialized by an algorithm-dependent method, and evolves towards successively better regions of the search space by means of (more or less) randomized processes of recombination, mutation, and selection. The environment delivers a quality information (fitness value) for new search points, and the selection process favors those individuals of higher quality to reproduce more often than worse individuals. The recombination mechanism allows for mixing of parental information while passing it to their descendants, and mutation introduces innovation into the population. This process is currently used by three different mainstreams of Evolutionary Algorithms, i.e. Evolution Strategies (ESs), Genetic Algorithms (GAs), and Evolutionary Programming (EP), details of which are presented in chapter 2. This chapter presents their biological background in order to have the necessary understanding of the basic natural processes (section 1.1). Evolutionary Algorithms are then discussed with respect to their impact on Artificial Intelligence and, at the same time, their interpretation as a technique for machine learning (section 1.2). Furthermore, their interpretation as a global optimization technique and the basic mathematical terminology as well as some convergence results on random search algorithms as far as they are useful for Evolutionary Algorithms are presented in section 1.3.
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Denevan, William M. "Pre-European Human Impacts on Tropical Lowland Environments." In The Physical Geography of South America. Oxford University Press, 2007. http://dx.doi.org/10.1093/oso/9780195313413.003.0025.
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The topic of early human impacts on New World environments, including Amazonia, is controversial as to degree and extent (Balée, 1989; Cleary, 2001; Denevan, 1992b; Gómez-Pompa and Kaus, 1992; Hayashida, 2005; Krech, 1999; Stahl, 1996; Vale, 2002). Certainly, whenever and wherever people were present, even sparse populations, there was some change in the landscape. People cannot live on the land and use plants and animals for subsistence and other needs without changing that land and the plants and animals present. Human-induced changes may involve equilibrium in which the natural ecosystem basically recovers, even though composition is changed, or in which the human ecosystem is sustainable; or the changes may involve disequilibrium in which the regenerative capacities (i.e., biological diversity and productivity) of either system are retarded or destroyed (i.e., degradation) (Sponsel, 1992). These changes may have been intentional or not, ephemeral or long lasting, localized or regional, onetime events or cumulative, highly visible or not readily apparent. Vegetation is the most widespread focus of change; other impacts have been on wildlife, soil, river patterns, microclimate, and the land surface itself. The forces of change are settlement, cultivation, grazing, hunting and gathering (foraging), burning, and various earthworks and river works. All of these impacts and forces were present in pre- European South America. Furthermore, native people “recognize that human beings, past and present . . . have affected the distribution of the biota and the formation of the landscape” (Balée, 2003: 285–286). “Far from being a wild world . . . the forest is perceived as a superhuman garden” by the Achuar in Ecuador (Descola, 1994: 324). Lacking written records, it is difficult to reconstruct early indigenous impacts, and any attempt to do so involves speculation and inference. Some alterations have persisted to the present, but most have been masked by either landscape recovery or by human destruction. Furthermore, nature and culture merge, the dichotomy being artificial, conceptual (Descola, 1994: 1–6). And some human disturbances that seem old are actually recent, but the reverse is also true. The distinction may be difficult to ascertain.
Conference papers on the topic "Biological artificial valve"
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Pengo, V., M. Boschello, P. Peruzzi, D. Pagotto, L. Schivazappa, and S. Dalla Volta. "PATIENTS WITH ARTIFICIAL BUT NOT BIOLOGICAL HEART VALVE PROSTHESIS PRESENT A HYPERCOAGULABILITY RELATED TO THE INTENSITY OF ANTICOAGULATION." In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1643878.
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Long term anticoagulant therapy is mandatory for patients with artificial heart valve prosthesis and is suggested for some patients with biological heart valve prosthesis. Oral anticoagulants reduce but not abolish thromboembolic complication in these patients. They act lowering the level of vitamin K-dependent coagulation factors and that in turn should result in a depression of "in vivo" thrombin formation. Fibrinopeptide A (FpA) is a good marker of thrombin formation and therefore we ascertained in several occasions the thrombin formation in 43 patients with artificial and 18 with biological heart valve prosthesis, all the patients being on oral anticoagulant treatment at least from 1 year. FpA was significantly higher in patients with artificial (determinations n = 138) with respect to biological (n=73) heart valve prosthesis (p 0.01). The FpA level in biological valves was close to that obtained in 22 not anticoagulated healthy subjects. When we divided FpA values in artificial heart valves according to the intensity of anticoagulation, we obtained a decreasing FpA mean levels with the increase of the degree of anticoagulation. In particular FpA values with an INR 4.5 were close to values obtained in healthy subjects. These data support the concept that patients with artificial heart valves are at higher risk of thromboembolism and therefore the intensity of anticoagulation should be different with respect to biological valves and probably a little higher than that recommended at the Leuven Consensus Conference.
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Meller, Michael, and Ephrahim Garcia. "Power Savings of a Variable Recruitment Hydraulic Artificial Muscle Actuation Scheme." In ASME 2014 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/smasis2014-7718.
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We investigate utilizing inelastic bladder hydraulic artificial muscle actuators as muscle fibers. These muscle fibers are then grouped together to form a variable recruitment artificial muscle bundle. This muscle bundle configuration is biologically inspired, where in skeletal muscle, different numbers of motor units are recruited to match the load by increasing the number of motor neurons firing. This results in extremely efficient locomotion in nature. It is desired to use a similar methodology to increase the actuation efficiency of valve-controlled hydraulic systems. Such hydraulic control systems induce a pressure drop in the valves to throttle the flow to the cylinder actuators. Using the valves in this manner is simple but very inefficient. Hence, this paper presents selectively recruiting different numbers of the hydraulic artificial muscle fibers to match a required loading scenario similar to our bipedal robot. By using fewer of the muscle fibers to match a smaller load, less power is consumed from the hydraulic power unit because instead of inducing a pressure drop, the volume of fluid delivered is decreased. The potential efficiency improvements associated with this actuation scheme is compared to a traditional hydraulic system with differential cylinders.
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Piovesan, Davide, and Michael J. Panza. "A Dissipative String Model for Human Tendons." In ASME 2014 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/detc2014-34304.
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This work presents an analytical modelling of a tendon driven system. We modelled the tendon as a continuum string using physiologically plausible value for the intrinsic characteristics of biological tissues to verify the system’s stability. We used Poincare’s sections to verify the types of attractors the system has and proved that the system is non-chaotic in a large range of physiologically plausible excitation frequencies. This work is relevant for understanding the control of force and movement as a function of the muscle contraction. Wide applications can also be found as a guideline for the design of artificial muscles and cable driven robots.
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Georgiev, Georgi. "BIOLOGICAL DIVERSITY OF WETLANDS AND RAMSAR PLACES IN THE CROSS-BORDER REGION OF BULGARIA, NORTHERN MACEDONIA, ALBANIA AND GREECE AND DEVELOPMENT." In TOURISM AND CONNECTIVITY 2020. University publishing house "Science and Economics", University of Economics - Varna, 2020. http://dx.doi.org/10.36997/tc2020.97.
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According to the definition of the International Union for Conservation of Nature and Natural Resources (IUCN), wetlands on Earth are areas that are flooded or saturated with water, artificial or natural, permanently or temporarily flooded with standing, sitting or running water. These areas include areas where water is the predominant element, such as swamps, wetlands, peatlands, estuaries, sea branches and lagoons, lakes, rivers and artificial reservoirs with a depth of more than six meters. Considering the importance of these territories and with the deep conviction that the preservation of their flora and fauna can be ensured by combining long-term national policy with coordinated international action, the scientific community reacted to the encroachments and unreasonable attitude to them by concluding 02.02. 1971 of the Convention on wetlands of international importance, especially as waterfowl habitats, known to the general public as the Ramsar Convention. The main objectives of this document are to manage wetlands as sites of great economic, cultural, scientific and conservation value, to avoid damage and loss and to preserve them through prudent use, i.e. through their continuous development. The object of study in the present work is the biological diversity, in particular the avifauna of some of the internationally important wetlands in the border areas between Bulgaria, Greece, the Republic of North Macedonia and Albania in view of the opportunities they offer for the development of some forms of alternative types of tourism.
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Hauert, R. "A Review of DLC Coatings for Biological Applications." In World Tribology Congress III. ASMEDC, 2005. http://dx.doi.org/10.1115/wtc2005-63879.
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Diamond-like carbon (DLC) is a class of materials with outstanding mechanical, tribological and biological properties. From in-vitro experiments, it is known that by incorporating other elements into the DLC film, the ratios of the different proteins adsorbed on the surface can be changed. These proteins will then subsequently control cell attachment, cell proliferation and cell differentiation. In a total hip joint replacement, the metallic femoral head, which slides against a polyethylene pan, causes polymeric wear debris. These wear particles may then trigger inflammatory reactions, resulting in osteolysis (bone resorption) and subsequent implant loosening. DLC has proven its outstanding tribological properties in many technical applications, mainly due to the build up of a transfer layer on the counterpart. DLC coated load bearing implants sliding against ultra high molecular weight polyethylene (UHMWPE) have been investigated. The different in-vitro experiments apparently showed contradicting results, mainly due to the different experimental setups and especially the different liquids used as lubricants. The synovial fluid present in a biological joint, contains large organic molecules which function as a boundary lubricants. Phospholipids, proteoglycans or proteins can be chemisorbed on the joint surfaces and trap water molecules, resulting in water acting as a viscose lubricant. When a DLC coated femoral head is tested against a polyethylene pan in a hip joint simulator, using synovial fluid as a lubricant, the build up of a transfer layer, protecting the softer counterpart (i.e. the polymer) does not seem to take place and the UHMWPE counterpart still shows wear. However, when DLC slides against DLC in medical applications, the build up of a transfer layer may not be a critical issue or is not drastically altered by the presence of proteins, and very low wear rates could be obtained in different in-vitro tests. Additionally, DLC coatings have an excellent haemocompatibility, which is expressed in a decreased thrombus formation. When exposed to blood, an increased ratio of albumin to fibrinogen adsorption, as well as decreased blood platelet activation is observed on coated surfaces. A few DLC coated cardiovascular implants such as artificial heart valves, blood pumps and stents are already commercially available. When coating a metal with DLC, good adhesion is obtained due to the about one nanometer thick metal-carbide reaction layer at the DLC/substrate interface. Upon implantation, it has to be guaranteed that this reaction layer is also chemically long-term stable under in-vivo conditions.
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Basham, Colin, Megan Pitz, Joseph Najem, Stephen Sarles, and Md Sakib Hasan. "Memcapacitive Devices in Neuromorphic Circuits via Polymeric Biomimetic Membranes." In ASME 2019 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/smasis2019-5648.
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Abstract Two-terminal adaptive materials and circuit elements that mimic the signal processing, learning, and computing capabilities of biological synapses are essential for next-generation computing systems. To this end, we have recently developed resistive (ion channel) and capacitive (lipid bilayer) memory elements that mimic the composition, structure, and plasticity of biological synapses. Unlike solid-state counterparts, these biomolecular systems are low-power, analog, less noisy, biocompatible, and capable of exhibiting multiple timescales of short-term synaptic plasticity. However, lipid membranes lack structural stability and modularity necessary for a long-lasting adaptive material system. To address this issue, we propose the replacement of phospholipids with amphiphilic polymers to create artificial membranes, which have been demonstrated to be more durable than phospholipids. With the focus on memory capacitors, we demonstrate that polymeric bilayers can exhibit pinched hysteresis in the Q-v plane because of voltage-induced geometrical changes. Further, we demonstrate that the memcapacitive response is altered based on the surrounding oil medium; smaller oil molecules are retained at higher volume in the membrane, so that thicker bilayers have lower nominal capacitance but can vary this value by over 400%. Finally, we present a physics-based model that enables us to predict the device’s areal voltage-dependent response. Polymeric bilayers represent a significant enhancement in the field of soft-matter, geometrically-reconfigurable memcapacitors, and their highly customizable compositions will allow for a finely tuned electrical response that has a future in brain-inspired materials and circuits.
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Mointire, V. L., A. J. Frangos, G. B. Rhee, G. S. Eskin, and R. E. Hall. "RHEOLOGY AND CELL ACTIVATION." In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1643988.
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The subject of this work is to examine the hypothesis that some sublytic levels of mechanical perturbation of cells can stimulate cell metabolism. As a marker metabolite, we have chosen arachidonic acid. Principal metabolites for platelets include the cyclooxygenase product thromboxane A2(TXA2) and the lipoxygenase product 12-hydroperoxy-eicosatetraenoic acid (12-HPETE). Polymorphonuclear leukocytes (PMNLs) initally produce principally 5-HPETE, somtimes leading to the formation leukotrienes, though many other metabolites of arachidonic acid have been isolated from activated neutrophils. Human umbilical vein endothelial cells utilize arachidonic acid to produce mainly prostaglandin I2(PGI2). All of these metabolites are biologically active and modulate cell function - sometimes in quite contrasting ways. We will show that levels of sublytic mechanical stress exposure can stimulate arachidonic acid metabolism in all three of the cell types mentioned above. The biological implications of this stress/metabolism coupling may be quite far reaching.Human platelets, leukocytes and endothelial cells all appear to be sensitive to mechanical stress induced activation of arachidonic acid metabolism. Sheared PRP exhibited greatly increased synthesis of 12-HETE and surprisingly little thromboxane B2 production. This indicates that shear stress stimulation of platelets may produce quite different arachidonic acid metabolism than that seen with many direct chemical stimuli, such as thrombin or collagen.Our data demonstrate that a substance derived from shear induced platelet activation may activate the C-5 lipoxygenase of human PMNL under stress, leading to the production of LTB4. We hypothesize that this substance maybe 12-HPETE. LTB4 is known to be a very potent chemotactic factor and to induce PMNL aggregation and degranulation. Our studies provide further evidence that lipoxygenase products of one cell type can modulate production of lipoxygenase products in a second cell type, and that shear stress can initiate cell activation. This kind of coupling could have far reaching implications in terms of our understanding of cell/cell interaction in flowing systems, such as acute inflammation, artificial organ implantation and tumor metastasis.The data on PGI2 production by endothelial cells demonstrate that physiological levels of shear stress can dramatically increase arachidonic acid metabolism. Step increases in shear stress lead to a burst in production of PGI2 which decayed to a steady state value in several minutes. This longer term stimulation of prostacyclin production rate increased linearly with shear stress over the range of 0-24 dynes/cm2. In addition, pulsatile flow of physiological frequency and amplitude caused approximately 2.4 times the PGI2 production rate as steady flow with the same mean stress. Although only PGI2 was measured, it is likely that other arachidonic acid metabolites of endothelial cells are also affected by shear stress.The ability of cells to respond to external stimuli involves the transduction of a signal across the plasma membrane. One such external stimulus appears to be fluid shear stress. Steady shear flow induces cell rotation in suspended cells, leading to a periodic membrane loading, with the peak stress proportional to the bulk shear stress. On anchorage-dependent cells, such as endothelial cells, steady shear stress may act by amplifying the natural thermal or Brownian fluttering or rippling of the membrane. There are several possible mechanisms by which shear stress induced membrane perturbation could mimic a hormone/receptor interaction, leading to increased intracellular metabolism. Shear stress may induce increased phospholipase C activity, caused by translocation of the enzyme, increased substrate (arachidonic acid) pool availability to phospholipase C (particularly from that stored in phosphoinositols) due to shear-induced membrane movements or changes in membrane fluidity, direct activation of calcium - activated phospholipase A2 by increased membrane calcium ion permeability, or most probably by a combination of these mechanisms.
Reports on the topic "Biological artificial valve"
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BARKHATOV, NIKOLAY, and SERGEY REVUNOV. A software-computational neural network tool for predicting the electromagnetic state of the polar magnetosphere, taking into account the process that simulates its slow loading by the kinetic energy of the solar wind. SIB-Expertise, December 2021. http://dx.doi.org/10.12731/er0519.07122021.
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The auroral activity indices AU, AL, AE, introduced into geophysics at the beginning of the space era, although they have certain drawbacks, are still widely used to monitor geomagnetic activity at high latitudes. The AU index reflects the intensity of the eastern electric jet, while the AL index is determined by the intensity of the western electric jet. There are many regression relationships linking the indices of magnetic activity with a wide range of phenomena observed in the Earth's magnetosphere and atmosphere. These relationships determine the importance of monitoring and predicting geomagnetic activity for research in various areas of solar-terrestrial physics. The most dramatic phenomena in the magnetosphere and high-latitude ionosphere occur during periods of magnetospheric substorms, a sensitive indicator of which is the time variation and value of the AL index. Currently, AL index forecasting is carried out by various methods using both dynamic systems and artificial intelligence. Forecasting is based on the close relationship between the state of the magnetosphere and the parameters of the solar wind and the interplanetary magnetic field (IMF). This application proposes an algorithm for describing the process of substorm formation using an instrument in the form of an Elman-type ANN by reconstructing the AL index using the dynamics of the new integral parameter we introduced. The use of an integral parameter at the input of the ANN makes it possible to simulate the structure and intellectual properties of the biological nervous system, since in this way an additional realization of the memory of the prehistory of the modeled process is provided.