The outer parenchyma of carrot was tested using dynamic mechanical analysis (DMA), in air with 90% humidity between 30 and 90°C. Temperature plots of storage (SM i.e. elastic) and loss (LM i.e. inelastic) moduli were obtained. The SM and LM values were the basis for the calculation of the loss tangent (LT), the parameter expressing the ratio of inelastic to elastic parenchyma toughness. As expected, the tissue toughness decreased with increasing temperature. For both moduli, two characteristic temperature areas with temperature slope minima were observed--they were termed low (I) and high (II) temperature negative peaks on the temperature slope plots. It was shown that the negative peaks were related to an increase in the inelastic part of the tissue toughness. All plots were dependent on the temperature rate: increasing the temperature rate (from 0.5 to 2°C/min) resulted in a shift of both the negative peaks I and II to higher temperatures, thereby reducing I and increasing II. It was shown that the observed behaviour cannot be described by simple kinetic equations due to the time dependent and complicated character of the thermally induced changes. These changes were interpreted as a consequence of pore protein denaturation followed by changes of the stress inside the parenchyma cells.

• MeSH
• kinetika MeSH
• kořeny rostlin fyziologie   MeSH
• mechanický stres MeSH
• modul pružnosti MeSH
• mrkev obecná fyziologie   MeSH
• teplota MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

• Klíčová slova
• extrémní dynamická zátěž, biomechanická analýza,
• MeSH
• biomechanika * fyziologie   MeSH
• kraniocerebrální traumata * etiologie   patologie   MeSH
• lidé MeSH
• matematické pojmy MeSH
• mechanické jevy MeSH
• soudní lékařství metody   trendy   MeSH
• statistika jako téma MeSH
• svalová síla fyziologie   MeSH
• teoretické modely * MeSH
• Check Tag
• lidé MeSH

Již staršími statickými metodami bylo prokázáno, že tření lyže ohřívá sníh. Vzniklá tenká vrstva vody umožňuje skluz lyže. Cílem naší studie bylo zjistit, zda i dynamická infračervená termografi e je schopna registrovat rychlé změny teploty sněhu v jednom určitém bodě před a po projetí lyže. Monitorovali jsme sníh ve stopě po 12 jízdách rekreačního běžce na lyžích různými rychlostmi, bez i s mazáním lyží a s různým zatížením lyží. Měření infračerveného záření a výpočet teploty na povrchu sněhu bezprostředně před a po projetí lyžaře bylo provedeno termografi ckým systémem FLIR SC620 s vzorkovací frekvencí 30 Hz. Byly zjištěno významné zvýšení teploty sněhu po projetí lyžaře (o 0,2 až 1,7°C), lineární závislost zahřátí sněhu na rychlosti a zvýšení teploty po namazání lyže. Studie potvrdila schopnost dynamické infračervené termografi e citlivě registrovat velmi rychlé teplotní změny sněhu v jednom bodě bezprostředně před a po (do 0,033 s) projetí běžce na lyžích. Otevírá se tak možnost dalšího studia rychlých termodynamických změn, které by přispělo k hlubšímu pochopení zákonitostí tření a skluzu v běžeckém lyžování.

The effect of ski friction on the snow temperature increasing is known. The made water film facilitates the ski moving. The aim of our pilot study was to ascertain a capability of the dynamic infrared thermography to register the quick thermal changes at determined point of snow before and aft er ski moving. We monitored snow aft er immediately before and aft er 12 runs of recreational cross-country skier by dynamic infrared thermography FLIR SC620 with image frequency 30 Hz. We found signifi cant increasing of snow temperature (by 0,2 to 1,7°C), linear dependence of snow warming on ski moving speed, and temperature increasing aft er ski waxing. The study confi rmed the dynamic infrared thermography ability to register very quick changes at determined point of snow temperature before and aft er (less than 0,033 s) cross-country skier moving. We have opened next thermodynamic studies for profound understanding of cross-country ski friction and gliding on snow.

• Klíčová slova
• běžecké lyžování, infračervená termografie,
• MeSH
• infračervené záření MeSH
• lidé MeSH
• mechanické jevy MeSH
• pilotní projekty MeSH
• sníh MeSH
• sporty na sněhu MeSH
• statistika jako téma MeSH
• teploměry využití   MeSH
• teplota MeSH
• termodynamika MeSH
• tření MeSH
• Check Tag
• lidé MeSH

A study of mechanical properties of native tissues is a great challenge in biomechanics. Especially, hardly accessible structures that play a very important role within a locomotive system. A study of a cartilaginous endplate (CEP) is just such a challenge. CEP is approximately 0.6 mm thin layer of hyaline cartilage between an intervertebral disc (IVD) and a vertebral body (VB). A calcification or any mechanical damage of CEP can cause restrictions of nutrition and metabolic waste flow inward and outward from IVD, respectively. Degenerative processes influence mechanical properties of the tissue. Due to very small thickness of CEP, instrumental nanoindentation seems to be suitable method for this task. This paper presents a study of time dependent viscoelastic properties of native porcine CEP using nanoscale dynamic mechanical analysis in the range of frequency from 5 Hz to 215 Hz. The storage moduli were obtained in the range from 11.78 MPa to 17.11 MPa. The loss moduli were obtained in the range from 2.96 MPa to 5.32 MPa.

• MeSH
• analýza metodou konečných prvků * využití   MeSH
• anatomické modely MeSH
• artroplastiky kloubů metody   využití   MeSH
• biomechanika MeSH
• chůze (způsob) MeSH
• elektromyografie metody   využití   MeSH
• klouby fyziologie   MeSH
• kosterní svaly MeSH
• kosti dolní končetiny * fyziologie   MeSH
• lidé MeSH
• mechanické jevy MeSH
• statistika jako téma MeSH
• teoretické modely MeSH
• zatížení muskuloskeletálního systému * fyziologie   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• práce podpořená grantem MeSH

Guanine radical cation (G•+) is a key intermediate in many oxidative processes occurring in nucleic acids. Here, by combining mixed Quantum Mechanical/Molecular Mechanics calculations and Molecular Dynamics (MD) simulations, we study how the structural behaviour of a tract GGG(TTAGGG)3 (hereafter Tel21) of the human telomeric sequence, folded in an antiparallel quadruple helix, changes when one of the G bases is ionized to G•+ (Tel21+). Once assessed that the electron-hole is localized on a single G, we perform MD simulations of twelve Tel21+ systems, differing in the position of G•+ in the sequence. When G•+ is located in the tetrad adjacent to the diagonal loop, we observe substantial structural rearrangements, which can decrease the electrostatic repulsion with the inner Na+ ions and increase the solvent exposed surface of G•+. Analysis of solvation patterns of G•+ provides new insights on the main reactions of G•+, i.e. the deprotonation at two different sites and hydration at the C8 atom, the first steps of the processes producing 8oxo-Guanine. We suggest the main structural determinants of the relative reactivity of each position and our conclusions, consistent with the available experimental trends, can help rationalizing the reactivity of other G-quadruplex topologies.

• MeSH
• DNA chemie   MeSH
• G-kvadruplexy * MeSH
• guanin chemie   MeSH
• ionty chemie   MeSH
• konformace nukleové kyseliny MeSH
• kvantová teorie * MeSH
• lidé MeSH
• molekulární modely MeSH
• oxidační stres * MeSH
• rozpustnost MeSH
• simulace molekulární dynamiky * MeSH
• telomery chemie   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH

BACKGROUND: The current generation of neonatal ventilators enables periodic storage of set, measured, and calculated ventilatory parameters. DESIGN: Retrospective observational study. OBJECTIVES: To evaluate and identify the ventilatory, demographic, and clinical pre-extubation variables that are significant for estimating extubation readiness. METHODS: Eligible subjects included premature infants <33 weeks of gestation weaned from mechanical ventilation (MV) lasting >24 h. A total of 16 relevant ventilator variables, each calculated from 288 data points over 24 h, together with eight demographic and three clinical pre-extubation variables, were used to create the generalized linear model (GLM) for a binary outcome and the Cox proportional hazards model for time-to-event analysis. The achievement of a 120-h period without reintubation was defined as a successful extubation attempt (EA) within the binary outcome. RESULTS: We evaluated 149 EAs in 81 infants with a median (interquartile range) gestational age of 25+2 (24+3-26+1) weeks. Of this, 90 EAs (60%) were successful while 59 (40%) failed. GLM identified dynamic compliance per kilogram, percentage of spontaneous minute ventilation, and postmenstrual age as significant independent positive variables. Conversely, dynamic compliance variability emerged as a significant independent negative variable for extubation success. This model enabled the creation of a probability estimator for extubation success with a good proportion of sensitivity and specificity (80% and 73% for a cut-off of 60%, respectively). CONCLUSIONS: Ventilator variables reflecting lung mechanical properties and the ability to spontaneously breathe during MV contribute to better prediction of extubation readiness in extremely premature infants with chronic lung disease.

• MeSH
• extubace * MeSH
• gestační stáří MeSH
• lidé MeSH
• mechanické ventilátory MeSH
• novorozenci extrémně nezralí * MeSH
• novorozenec MeSH
• odpojení od ventilátoru * metody   MeSH
• retrospektivní studie MeSH
• umělé dýchání * metody   MeSH
• Check Tag
• lidé MeSH
• mužské pohlaví MeSH
• novorozenec MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• pozorovací studie MeSH

The aim of the study was to determine the relationship between implant-associated complications and Dynamic Hip Screw (DHS) placement in the femoral neck, based on a Finite Element (FE) Analysis. Very diverse implant failures and subsequent complications can be encountered after introduction of the DHS. We evaluated 308 dynamic hip screw osteosyntheses for pertrochanteric fractures in 297 patients. The ABAQUS 6.9 program was used for development of the FE model, and the analyses were performed in 5 modelled situations corresponding to five different screw locations. Complications occurred in 10% of patients and re-operation was necessary in 3.9%. The highest risk of implant failure was associated with the screw situation in the upper third of the femoral neck. Placing a dynamic hip screw in the middle third of the neck significantly reduced stresses in the plate and screw. The screw position in the upper third of the neck significantly increased these stresses. The finite element analysis confirmed our clinical experience that the optimum position of the dynamic hip screw is in the middle third of the femoral neck.

• MeSH
• analýza selhání vybavení * metody   statistika a číselné údaje   MeSH
• fraktury krčku femuru * chirurgie   radiografie   MeSH
• fraktury kyčle chirurgie   radiografie   MeSH
• kostní šrouby MeSH
• lidé středního věku MeSH
• lidé MeSH
• mechanický stres MeSH
• počítačová simulace MeSH
• reoperace statistika a číselné údaje   MeSH
• senioři nad 80 let MeSH
• senioři MeSH
• vnitřní fixace fraktury * metody   přístrojové vybavení   škodlivé účinky   MeSH
• Check Tag
• lidé středního věku MeSH
• lidé MeSH
• mužské pohlaví MeSH
• senioři nad 80 let MeSH
• senioři MeSH
• ženské pohlaví MeSH
• Publikační typ
• práce podpořená grantem MeSH
• srovnávací studie MeSH

Study of the relationship between ventilation parameters: monitored expiratory time constant - tau(edyn) and breathing - trigger frequency (f(trig)) and time of breathing cycle (T(cy)) are main goals of this article. Parameters were analyzed during last 4+/-2 h before weaning from ventilation in 66 patients ventilated in pressure support mode (PSV). We have found out, that there exist mathematical relationships, observed during adequate gas exchange, yet not described. Monitored parameters are represented by tau(edyn), f(trig) and T(cy). The analysis showed close negative correlation between T(cy) and f(trig) (R(2)=0.903). This implies that each increasing of tau(edyn) causes decreasing of f(trig) and vice versa. The calculation of regression equation between tau(edyn) and T(cy) outlined that T(cy) = 5.2625 * tau(edyn) + 0.1242 (R(2)=0.85). Regulation of respiratory cycles by the respiratory center in the brain is probably based on evaluation of tau(edyn) as the tau(edyn) probably represents a regulatory element and T(cy) regulated element. It can be assumed, that respiratory center can optimize the work of breathing in order to minimize energy in system patient + ventilator. The unique relationship, described above could be useful in clinical practice for development of new ventilation modes.

• MeSH
• časové faktory MeSH
• lidé středního věku MeSH
• lidé MeSH
• mechanika dýchání fyziologie   MeSH
• odpojení od ventilátoru metody   MeSH
• retrospektivní studie MeSH
• senioři MeSH
• umělé dýchání metody   MeSH
• ventilace umělá s výdechovým přetlakem metody   MeSH
• vydechnutí fyziologie   MeSH
• Check Tag
• lidé středního věku MeSH
• lidé MeSH
• mužské pohlaví MeSH
• senioři MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH

Service life assessment of three historical building envelopes constructed using different types of sandstone is presented. At first, experimental measurements of material parameters of sandstones are performed to provide the necessary input data for a subsequent computational analysis. In the second step, the moisture and temperature fields across the studied envelopes are calculated for a representative period of time. The computations are performed using dynamic climatic data as the boundary conditions on the exterior side of building envelope. The climatic data for three characteristic localities are experimentally determined by the Czech Hydrometeorological Institute and contain hourly values of temperature, relative humidity, rainfalls, wind velocity and direction, and sun radiation. Using the measured durability properties of the analyzed sandstones and the calculated numbers of freeze/thaw cycles under different climatic conditions, the service life of the investigated building envelopes is assessed. The obtained results show that the climatic conditions can play a very significant role in the service life assessment of historical buildings, even in the conditions of such a small country as the Czech Republic. In addition, the investigations reveal the importance of the material characteristics of sandstones, in particular the hygric properties, on their service life in a structure.

• MeSH
• konstrukční materiály analýza   MeSH
• lidé MeSH
• mechanické jevy MeSH
• teoretické modely MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH