Contribution of postnatal collagen reorientation to depth-dependent mechanical properties of articular cartilage

The collagen fibril network is an important factor for the depth-dependent mechanical behaviour of adult articular cartilage (AC). Recent studies show that collagen orientation is parallel to the articular surface throughout the tissue depth in perinatal animals, and that the collagen orientations transform to a depth-dependent arcade-like structure in adult animals. Current understanding on the mechanobiology of postnatal AC development is incomplete. In the current paper, we investigate the contribution of collagen fibril orientation changes to the depth-dependent mechanical properties of AC. We use a composition-based finite element model to simulate in a 1-D confined compression geometry the effects of ten different collagen orientation patterns that were measured in developing sheep. In initial postnatal life, AC is mostly subject to growth and we observe only small changes in depth-dependent mechanical behaviour. Functional adaptation of depth-dependent mechanical behaviour of AC takes place in the second half of life before puberty. Changes in fibril orientation alone increase cartilage stiffness during development through the modulation of swelling strains and osmotic pressures. Changes in stiffness are most pronounced for small stresses and for cartilage adjacent to the bone. We hypothesize that postnatal changes in collagen fibril orientation induce mechanical effects that in turn promote these changes. We further hypothesize that a part of the depth-dependent postnatal increase in collagen content in literature is initiated by the depth-dependent postnatal increase in fibril strain due to collagen fibril reorientatio

The effect of trimming of the frog on the impact accelerations of the equine hoof during walk and trot

Bij conventioneel bekapte hoeven heeft de straal niet tot nauwelijks contact met de grond. Het wordt verondersteld dat de energieabsorberende functie van de straal hierbij gereduceerd is of mogelijk zelfs vrijwel afwezig is. Het valt te verwachten dat een hoef waarvan de straal een goed contact maakt met de ondergrond een geringere impactversnelling zal hebben dan een hoef waarvan de straal niet of nauwelijks de grond raakt.Om deze hypothese te testen ondergingen 10 klinisch gezonde warmbloedpaarden drie achtereenvolgende behandelingen; 1. Onbekapt (controle meting); 2. Bekapte hoefwand + onbekapte straal; 3. Bekapte hoefwand + bekapte straal.het bekappen van de straal lijkt geen invloed te hebben op bovenstaande parameters. Het is echter niet uit te sluiten dat er bij een andere proefopzet(bijvoorbeeld bij lopen op een betonvloer) wel verschillen gevonden kunnen worde

Environmental Flow Regimes for Dysidea avara Sponges

The aim of our research is to design tank systems to culture Dysidea avara for the production of avarol. Flow information was needed to design culture tanks suitable for effective production. Water flow regimes were characterized over a 1-year period for a shallow rocky sublittoral environment in the Northwestern Mediterranean where D. avara sponges are particularly abundant. Three-dimensional Doppler current velocities at 8¿10-m depths ranged from 5 to 15 cm/s over most seasons, occasionally spiking to 30¿66 cm/s. A thermistor flow sensor was used to map flow fields in close proximity (¿2 cm) to individual sponges at 4.5-, 8.8-, and 14.3-m depths. These ¿proximal flows¿ averaged 1.6 cm/s in calm seas and 5.9 cm/s during a storm, when the highest proximal flow (32.9 cm/s) was recorded next to a sponge at the shallowest station. Proximal flows diminished exponentially with depth, averaging 2.6 cm/s¿±¿0.15 SE over the entire study. Flow visualization studies showed that oscillatory flow (0.20¿0.33 Hz) was the most common regime around individual sponges. Sponges at the 4.5-m site maintained a compact morphology with large oscula year-around despite only seasonally high flows. Sponges at 8.8 m were more erect with large oscula on tall protuberances. At the lowest-flow 14.3-m site, sponges were more branched and heavily conulated, with small oscula. The relationship between sponge morphology and ambient flow regime is discussed

Optimum prey capture techniques in fish

In this thesis hydrodynamic principles are used to quantify relations between form and function in the prey capture mechanism of actinopterygian fish. This work is closely related to the papers on the hydrodynamics of fish feeding by Muller et al. (1982) and Muller & Osse (in press). The effectiveness of different head forms and movements for prey uptake (in various habitats) is investigated by model simulations and verified by flow visualization and pressure measurements.Chapter 1 presents a technique to visualize the flow in 3-D around the mouth of the fish, sucking its prey. An expanding and compressing cylindrical or conical model of the fish's mouth cavity is used to quantify the relation between head movements and swimming. The opercular and branchiostegal valves are shown to function as control devices to obtain an optimal flow rate through the mouth aperture. The theoretical predictions were verified experimentally for the rainbow trout ( Salmo gairdneri ). Likewise, data from the literature appeared to agree with these hypotheses.Chapter 2 quantifies the contributions of the forward movement of the fish, the expansion of the mouth cavity and a possible protrusion of the jaws to the velocity of the prey. Optimum sucking techniques (i.e. techniques maximizing the chance of prey capture) in relation to swimming speed and habitat properties are derived by model simulations. Maximization of the initial prey distance by an exact adjustment of mouth expansion is rather useless for a fish. Much more is gained if the fish abducts its opercula at the maximal rate when the prey enters the mouth.Chapter 3 discusses recording techniques for pressures in prey-sucking fish. The dynamic properties of different measurement systems are investigated by Fourier analysis. Also, the frequency content of records of the fluctuating pressure inside the fish's mouth during feeding is shown. Prey capture events of different fish species are simulated using the hydrodynamical model of Muller et al. (1982). Measured and simulated pressure curves are compared and the effects of the use of different boundary conditions in the model are discussed. The literature on pressure measurements in prey-sucking fish is reviewed

Еволюція топоформанта -щина в слов’янських мовах та його рефлекси в реґіональній історичній ойконімії

У статті автор на широкому географічно-історичному тлі простежує еволюцію топоформанта -щина в слов'янській топонімії детально аналізує рефлекси цього суфікса в реґіональній історичній ойконімії на прикладі дев'яти назв (і 12-ти мікроойконімних варіантів) населених пунктів Галицької та Львівської земель Руського воєводства із подальшим встановленням їхньої етимологи.В статье автор на широком географическо-историческом фоне прослеживает эволюцию топонимического форманта -щина в славянской топонимии детально анализирует рефлексы этого суффикса в региональной исторической ойконимии на примере девяти названий (с 12-ю микроойконимными вариантами) населенных пунктов Галицкой и Львовской земель Русского воеводства с последующим установлением их этимологии.The author traces the evolution of topoformant -schyna on the basis of historical and geographical studies in Slavic Toponymy. Reflexes of the suffix are analyzed in regional historical oykonymy in 12 toponyms (and their 12 microokonymic variants) of villages and towns of Halych and Lviv Lands of Ruske Woyewodstwo. Their etymology is also analysed

Antagonistic effects of transforming growth factor-beta on vitamin D3 enhancement of osteocalcin and osteopontin transcription: reduced interactions of vitamin D receptor/retinoid X receptor complexes with vitamin E response elements

Osteocalcin and osteopontin are noncollagenous proteins secreted by osteoblasts and regulated by a complex interplay of systemic and locally produced factors, including growth factors and steroid hormones. We investigated the mechanism by which transforming growth factor-beta (TGF beta) inhibits 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3)-enhanced expression of the osteocalcin (OC) and osteopontin (OP) genes. ROS 17/2.8 cells, in which both genes are expressed, were transfected with reporter constructs driven by native (i.e. wild-type) rat OC and mouse OP promoters. TGF beta abrogated the 1,25-(OH)2D3 enhanced transcription of both the OC and OP genes. The inhibitory TGF beta response for each requires vitamin D response element (VDRE) sequences, although there are additional contributions from proximal basal regulatory elements. These transcriptional effects were further investigated for contribution of the trans-activating factors, which interact with OC and OP VDREs, involving the vitamin D receptor (VDR) and retinoid X receptor (RXR). Gel mobility shift assays show that TGF beta significantly reduces induction of the heterodimers VDR/RXR complexes in 1,25-(OH)2D3-treated ROS 17/2.8 cells. However, Western blot and ligand binding analysis reveal that TGF beta does not affect nuclear availability of the VDR. We also show that activator protein-1 activity is up-regulated by TGF beta; thus, activator protein-1 binding sites in the OC promoter may potentially contribute to inhibitory effects of TGF beta on basal transcription. Our studies demonstrate that the inhibitory action of TGF beta on the 1,25-(OH)2D3 enhancement of OC and OP transcription in osteoblastic cells results from modulations of protein-DNA interactions at the OC and OP VDRE, which cannot be accounted for by changes in VDR protein levels. As OC and OP participate in bone turnover, our results provide insight into the contributions of TGF beta and 1,25-(OH)2D3 to VDR-mediated gene regulatory mechanism operative in bone formation and/or resorption events

Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: influence of the surface and of the inter-particle interactions

We study the magnetic properties of spherical Co clusters with diameters between 0.8 nm and 5.4 nm (25 to 7500$ atoms) prepared by sequential sputtering of Co and Al2O3. The particle size distribution has been determined from the equilibrium susceptibility and magnetization data and it is compared to previous structural characterizations. The distribution of activation energies was independently obtained from a scaling plot of the ac susceptibility. Combining these two distributions we have accurately determined the effective anisotropy constant Keff. We find that Keff is enhanced with respect to the bulk value and that it is dominated by a strong anisotropy induced at the surface of the clusters. Interactions between the magnetic moments of adjacent layers are shown to increase the effective activation energy barrier for the reversal of the magnetic moments. Finally, this reversal is shown to proceed classically down to the lowest temperature investigated (1.8 K).Comment: 13 figures submitted to Phys. Rev.

Water Management Solution of Reservoir Storage Function Under Condition of Measurement Uncertainties in Hydrological Input Data

AbstractThe paper describes a possible procedure of the rate uncertainty implementation to the continuous water stage measurement and uncertainties of state - discharge rating curve point positions, which the stage -discharge rating curves were fitted into the uncertainties of the real discharge series members. Then the members of discharge series under uncertainty impact were tested on the calculated values of the reservoir storage volume. The next step was the implementation of the uncertainties of the real discharge series members on the generation of the artificial discharge series of mean monthly discharge using the AR and ARMA generators and the determination of their impact on the calculated values of the reservoir storage volume