Distributed element
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- MeSH
- látky znečišťující životní prostředí analýza MeSH
- lidé MeSH
- neutronová aktivační analýza MeSH
- oči chemie MeSH
- stopové prvky analýza MeSH
- tkáňová distribuce MeSH
- vlasy, chlupy chemie MeSH
- Check Tag
- lidé MeSH
- mužské pohlaví MeSH
- ženské pohlaví MeSH
- Geografické názvy
- Československo MeSH
Willows (Salix spp.) are considered to be effective for the phytoremediation of trace elements from contaminated soils, but their efficiency is limited in heavily polluted soils because of poor growth. Liming can be a desirable measure to decrease the plant availability of elements, resulting in improved plant development. Notably, large root area and maximum soil penetration are basic parameters that improve the efficiency of phytoremediation. The impact of soil chemical properties on willow root anatomy and the distribution of trace elements below-ground have rarely been studied. The effect of liming on root parameters, biomass allocation and trace element distribution in non-harvestable (coarse roots, fine roots, stumps) and harvestable plant parts (twigs and leaves) of Salix × smithiana was assessed at the end of a 4-year pot experiment with two trace element-polluted soils that differed in terms of soil pH. Stump biomass predominated in weakly acidic soil. In neutral soil, the majority of biomass was located in fine roots and stumps; the difference from other plant parts was minor. Trace elements were the most concentrated in fine roots. Translocation to above-ground biomass increased as follows: Pb < As < Zn~Cd. In contrast to Cd and Zn, great differences in As and Pb mobility in plants were recorded after measurements of individual below-ground biomass (stumps < coarse roots < fine roots). Lime application decreased the concentrations of mobile Cd and Zn and related levels in plants, improved biomass production and root parameters and increased the removal of all trace elements in weakly acidic soil. None or minimum differences in the monitored parameters were recorded for dolomite treatments in both soils. The dose and source of liming had crucial effects on root anatomy. Growing willows in limed trace element-polluted soils is a suitable measure for combination of two remediation strategies, i.e. phytoextraction of Cd and Zn and assisted phytostabilization of As and Pb.
- MeSH
- biodegradace MeSH
- biomasa MeSH
- kořeny rostlin anatomie a histologie účinky léků MeSH
- látky znečišťující půdu analýza metabolismus MeSH
- oxidy chemie MeSH
- půda chemie MeSH
- Salix účinky léků růst a vývoj metabolismus MeSH
- sloučeniny vápníku chemie MeSH
- stopové prvky analýza metabolismus MeSH
- těžké kovy analýza metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
Úvod a cíl práce: Mechanický přenos zatížení na kost ovlivňuje kromě materiálových vlastností implantátu (mikrodesign), zejména typ použitého závitu a jeho parametry (makrodesign). Rozeznáváme čtyři základní tvary závitů: a) metrický, b) plochý, c) pilovitý, d) obrácený pilovitý a dva modifikované tvary podle ISO TC 150 normy: e) ISO Shallow HA kortikální a f) ISO Deep HB spongiózní. Mechanický přenos charakterizuje míru přenosu mechanického napětí ze závitu do kosti a je menší než jedna. V ideálním případě je roven jedné, ale vlivem odlišné pevnosti a pružnosti kosti a materiálu závitu je obtížné této hodnoty dosáhnout. Byly stanoveny dva cíle studie. Prvním bylo zjistit rozložení napjatosti (tj. tlakového, tahového a smykového napětí) nejčastěji používaných typů závitů zubních implantátů na rozhraní implantát – kost. Druhým cílem byl popis mechanické kompatibility (čili mechanického přenosu zatížení z implantátu na okolní kost) u stejných typů závitů. Metody: Pro modelování vlivu tvaru závitu implantátu na rozložení napětí v místě rozhraní implantát – kost jsme použili metodu konečných prvků v programu MSC Marc (MSC Software s.r.o., ČR) a metodiku podle Gefena, při které jsme analýze podrobili celou délku kontaktu implantátu s kostí. Definování okrajových podmínek. Velikost zatěžující síly byla F = 100 N, směr síly byl totožný s dlouhou osou implantátu a působiště síly bylo v jeho krčkové části.Charakterizování materiálového modelu. K popisu materiálových vlastností kosti jsme použili izotropní model, který definují dvě konstanty: Youngův modul pružnosti (E) a Poissonovo číslo (μ).Definování typu úlohy. Model byl simulován jako prostorová osově symetrická úloha. Výsledky: Z hlediska tahového napětí se ukazuje jako nejlepší závit ISO Shallow HA, v případě tlakového a smykového napětí se jeví nejvhodnějším plochý závit. Výsledky spočítané metodou konečných prvků u všech typů simulovaných závitů potvrzují, že v závitovém spojení je největší podíl napětí soustředěn v prvních cervikálních závitech. Diskuse a závěr: Z provedených simulací plyne, že profil závitu hraje významnou roli v ovlivnění velikosti a rozložení napětí v okolní kosti a mechanické kompatibility. Naše matematická studie neprokazuje, že existuje jeden ideální závit pro dentální implantát.
Introduction, Aim: Mechanical transfer of load onto the bone affects, besides implant material properties (microdesign), especially the type of thread used and its parameters (macrodesign). There are four basic types of thread: a) metric, b) flat, c) saw-tooth, d) inverted saw-tooth and two modified shapes as specified in standard ISO TC 150: e) ISO Shallow HA cortical, and f) ISO Deep HB cancellous. Mechanical transfer is a characteristic of the rate of mechanical stress transfer from thread to bone, which is less than one. The value of one constitutes an ideal situation but due to different strengths and elasticities in the bone and in the thread material, respectively, this value is difficult to achieve. Two objectives were set for the study. The one was to establish stress (tensile, compressive, and shear) distribution with the most used types of dental implant threads at the implant bone contact. The other objective was to characterize mechanical compatibility (or mechanical transfer of load from implant onto adjacent bone) with the same types of thread. Methods: The Finite Element Method using MSC Marc (MSC Software s.r.o.) program and methodology by Amit Gefen were utilized while the entire implant bone contact length was analysed. The model generation process consists of three stages. Definition of boundary conditions. The load force was F = 100N, direction of force was identical with the implant longitudinal axis while the origin of force was at its cervical area.Establishing material model characteristics. Isotropic model, specified with two constants, was used to establish characteristics of material properties: Young’s modulus of elasticity (E) and Poisson’s ratio (μ)Task specifications. The model was simulated as a 3D axisymmetric task. Results: The ISO Shallow HA thread comes out as the best one from the tensile stress’s point of view whereas the flat thread appears to be the most convenient when considering compressive or shear stress. The results computed using the Finite Element Method with all types of threads simulated confirm that the largest part of stress in threaded connection is found in the foremost cervical turns of thread. Discussion and Conclusion: The simulations carried out implicate that the thread cross section shape plays an important role in affecting stress amplitude and distribution adjacent to the bone as well as mechanical compatibility. Our mathematical study does not prove that there is one single ideal type of thread for dental implants.
- Klíčová slova
- dentální implantát, analýza konečných prvků, mechanická kompatibilita, napětí, závit,
- MeSH
- analýza metodou konečných prvků * statistika a číselné údaje MeSH
- kostní šrouby MeSH
- mechanický stres * MeSH
- návrh zubní náhrady MeSH
- pevnost v tahu MeSH
- pevnost ve smyku MeSH
- počítačová simulace MeSH
- zubní implantáty * klasifikace normy MeSH
- Publikační typ
- hodnotící studie MeSH
This study investigated the effect of implant thickness and material on deformation and stress distribution within different components of cranial implant assemblies. Using the finite element method, two cranial implants, differing in size and shape, and thicknesses (1, 2, 3 and 4 mm, respectively), were simulated under three loading scenarios. The implant assembly model included the detailed geometries of the mini-plates and micro-screws and was simulated using a sub-modeling approach. Statistical assessments based on the Design of Experiment methodology and on multiple regression analysis revealed that peak stresses in the components are influenced primarily by implant thickness, while the effect of implant material is secondary. On the contrary, the implant deflection is influenced predominantly by implant material followed by implant thickness. The highest values of deformation under a 50 N load were observed in the thinnest (1 mm) Polymethyl Methacrylate implant (Small defect: 0.296 mm; Large defect: 0.390 mm). The thinnest Polymethyl Methacrylate and Polyether Ether Ketone implants also generated stresses in the implants that can potentially breach the materials' yield limit. In terms of stress distribution, the change of implant thickness had a more significant impact on the implant performance than the change of Young's modulus of the implant material. The results indicated that the stresses are concentrated in the locations of fixation; therefore, the detailed models of mini-plates and micro-screws implemented in the finite element simulation provided a better insight into the mechanical performance of the implant-skull system.
INTRODUCTION AND HYPOTHESIS: Objective of this study was to develop an MRI-based finite element model and simulate a childbirth considering the fetal head position in a persistent occiput posterior position. METHODS: The model involves the pelvis, fetal head and soft tissues including the levator ani and obturator muscles simulated by the hyperelastic nonlinear Ogden material model. The uniaxial test was measured using pig samples of the levator to determine the material constants. Vaginal deliveries considering two positions of the fetal head were simulated: persistent occiput posterior position and uncomplicated occiput anterior position. The von Mises stress distribution was analyzed. RESULTS: The material constants of the hyperelastic Ogden model were measured for the samples of pig levator ani. The mean values of Ogden parameters were calculated as: μ1 = 8.2 ± 8.9 GPa; μ2 = 21.6 ± 17.3 GPa; α1 = 0.1803 ± 0.1299; α2 = 15.112 ± 3.1704. The results show the significant increase of the von Mises stress in the levator muscle for the case of a persistent occiput posterior position. For the optimal head position, the maximum stress was found in the anteromedial levator portion at station +8 (mean: 44.53 MPa). For the persistent occiput posterior position, the maximum was detected in the distal posteromedial levator portion at station +6 (mean: 120.28 MPa). CONCLUSIONS: The fetal head position during vaginal delivery significantly affects the stress distribution in the levator muscle. Considering the persistent occiput posterior position, the stress increases evenly 3.6 times compared with the optimal head position.
New Year's Eve fireworks represent one of the most unusual atmospheric pollution events in the course of a year. A majority of particles aerosolized by burning of fireworks consist of metals and their compounds used in firework displays. In this study, ambient particulate matter was sampled using a 14 stage cascade impactor in two European cities during turn of the years 2016/17 and 2017/18. Concentrations of 33 elements were determined by inductively coupled plasma mass spectrometry. To assess the impact of New Year's Eve fireworks on ambient air quality, chemically resolved size distributions of particles with diameters between 15 nm and 10 μm collected during fireworks episodes were compared to ones collected in normal winter weeks. For some metals a distinct shift of their concentration maximum related to fireworks could be observed, which is in between the maxima for accumulation and coarse mode particles. Concentrations of these elements (Sr, Ba, Mg, Bi, Al, Cu and K) were also higher during weeks with fireworks episodes than during control weeks. Although New Year's Eve fireworks only take place once a year, these results show that air pollution caused by fireworks can be a potential health risk, especially for people with pre-existing diseases.
- MeSH
- dovolená MeSH
- látky znečišťující vzduch analýza MeSH
- monitorování životního prostředí * MeSH
- pevné částice analýza MeSH
- prvky MeSH
- velikost částic MeSH
- velkoměsta MeSH
- výbušné látky analýza MeSH
- znečištění ovzduší analýza MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Geografické názvy
- Česká republika MeSH
- Rakousko MeSH
- velkoměsta MeSH
The finite element analysis (FEA) has been identified as a useful tool for the stress and strain behaviour determination in lower limb prosthetics. The residual limb and prosthetic socket interface was the main subject of interest in previous studies. This paper focuses on the finite element analysis for the evaluation of structural behaviour of the Sure-flex™ prosthetic foot and other load-bearing components. A prosthetic socket was not included in the FEA. An approach for the finite element modelling including foot analysis, reverse engineering and material property testing was used. The foot analysis incorporated ground reaction forces measurement, motion analysis and strain gauge analysis. For the material model determination, non-destructive laboratory testing and its FE simulation was used. A new, realistic way of load application is presented along with a detailed investigation of stress distribution in the load-bearing components of the prosthesis. A novel approach for numerical and experimental agreement determination was introduced. This showed differences in the strain on the pylon between the experimental and the numerical model within 30% for the anteroposterior bending and up to 25% for the compression. The highest von Mises stresses were found on the foot-pylon connecting component at toe off. Peak stress of 216MPa occurred on the posterior adjusting screw and maximum stress of 156MPa was found at the neck of the male pyramid.
- MeSH
- amputovaní MeSH
- analýza metodou konečných prvků MeSH
- dospělí MeSH
- lidé MeSH
- mechanický stres MeSH
- protézy - design MeSH
- protézy a implantáty MeSH
- tibie MeSH
- zatížení muskuloskeletálního systému MeSH
- Check Tag
- dospělí MeSH
- lidé MeSH
- mužské pohlaví MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
INTRODUCTION AND HYPOTHESIS: During vaginal delivery, the levator ani muscle (LAM) undergoes severe deformation. This stress can lead to stretch-related LAM injuries. The objective of this study was to develop a sophisticated MRI-based model to simulate changes in the LAM during vaginal delivery. METHODS: A 3D finite element model of the female pelvic floor and fetal head was developed. The model geometry was based on MRI data from a nulliparous woman and 1-day-old neonate. Material parameters were estimated using uniaxial test data from the literature and by least-square minimization method. The boundary conditions reflected all anatomical constraints and supports. A simulation of vaginal delivery with regard to the cardinal movements of labor was then performed. RESULTS: The mean stress values in the iliococcygeus portion of the LAM during fetal head extension were 4.91-7.93 MPa. The highest stress values were induced in the pubovisceral and puborectal LAM portions (mean 27.46 MPa) at the outset of fetal head extension. The last LAM subdivision engaged in the changes in stress was the posteromedial section of the puborectal muscle. The mean stress values were 16.89 MPa at the end of fetal head extension. The LAM was elongated by nearly 2.5 times from its initial resting position. CONCLUSIONS: The cardinal movements of labor significantly affect the subsequent heterogeneous stress distribution in the LAM. The absolute stress values were highest in portions of the muscle that arise from the pubic bone. These areas are at the highest risk for muscle injuries with long-term complications.
- MeSH
- analýza metodou konečných prvků * MeSH
- anatomické modely * MeSH
- biomechanika MeSH
- distorze a distenze etiologie MeSH
- dospělí MeSH
- hlava anatomie a histologie MeSH
- kosterní svaly zranění MeSH
- lidé MeSH
- magnetická rezonanční tomografie MeSH
- novorozenec MeSH
- pánevní dno anatomie a histologie diagnostické zobrazování fyziologie MeSH
- plod anatomie a histologie MeSH
- pružnost MeSH
- těhotenství MeSH
- vedení porodu škodlivé účinky MeSH
- zobrazování trojrozměrné metody MeSH
- Check Tag
- dospělí MeSH
- lidé MeSH
- novorozenec MeSH
- těhotenství MeSH
- ženské pohlaví MeSH
- Publikační typ
- časopisecké články MeSH
Dental implant dimensions, and bone quality and quantity play a key role in early osseointegration and long-term prognosis in posterior edentulous maxilla. Treatment with short implants, preferably in a bicortical manner, is an accepted modality; however, short implants have limitations leading to increased stress concentrations in alveolar bone, potential overload and implant failure. Implant models of 3.3, 4.1, 4.8 and 5.4 mm diameter and 4.5, 5.5, 6.5, 7.5 and 8.5 mm length were placed in posterior maxilla 3-D models with corresponding residual bone heights. Bone-implant assemblies were analyzed in finite element software ANSYS 15. All materials were assumed to be linearly elastic and isotropic. 118.2 N oblique loading was applied to investigate stress distributions in bone tissues. The concept of ultimate functional load (UFL) was selected as a criterion to compare load-carrying capacity of implants and to evaluate the influence of available bone height and implant dimensions on load-carrying capacity. For all implants, UFL was calculated by limiting von Mises stresses in cortical or cancellous bone with bone strength (100 MPa for cortical and 2 MPa for cancellous bone). Implant load-carrying capacity depends on diameter and available bone height. Wide implants have higher load-carrying capacity than narrow implants. Short implants with proper diameter and length avoid bone overstress, even in Type IV bone.
