Using molecular mechanics to predict bulk material properties of fibronectin fibers

The structural proteins of the extracellular matrix (ECM) form fibers with finely tuned mechanical properties matched to the time scales of cell traction forces. Several proteins such as fibronectin (Fn) and fibrin undergo molecular conformational changes that extend the proteins and are believed to be a major contributor to the extensibility of bulk fibers. The dynamics of these conformational changes have been thoroughly explored since the advent of single molecule force spectroscopy and molecular dynamics simulations but remarkably, these data have not been rigorously applied to the understanding of the time dependent mechanics of bulk ECM fibers. Using measurements of protein density within fibers, we have examined the influence of dynamic molecular conformational changes and the intermolecular arrangement of Fn within fibers on the bulk mechanical properties of Fn fibers. Fibers were simulated as molecular strands with architectures that promote either equal or disparate molecular loading under conditions of constant extension rate. Measurements of protein concentration within micron scale fibers using deep ultraviolet transmission microscopy allowed the simulations to be scaled appropriately for comparison to in vitro measurements of fiber mechanics as well as providing estimates of fiber porosity and water content, suggesting Fn fibers are approximately 75% solute. Comparing the properties predicted by single molecule measurements to in vitro measurements of Fn fibers showed that domain unfolding is sufficient to predict the high extensibility and nonlinear stiffness of Fn fibers with surprising accuracy, with disparately loaded fibers providing the best fit to experiment. This work shows the promise of this microstructural modeling approach for understanding Fn fiber properties, which is generally applicable to other ECM fibers, and could be further expanded to tissue scale by incorporating these simulated fibers into three dimensional network models

Sensitivity to horizontal and vertical corrugations defined by binocular disparity

AbstractSensitivity to corrugations defined by binocular disparity differs as a function of the modulation frequency. Such functions have proved to be useful descriptive and analytical tools in the study of the mechanisms involved in disparity processing. Indeed, given certain assumptions, these sensitivity functions can be used to predict certain perceptual outcomes. Given their importance, it is surprising that there is no comprehensive data set of disparity sensitivity functions (DSF) for a range of observers over a broad range of spatial frequencies and orientations. Here we report DSFs for six observers over an eight octave range of sinusoidal corrugations in disparity (0.0125–3.2 cpd). Multi-cycle, low frequency surfaces were used to assess the degree to which the fall-off in sensitivity at low corrugation frequencies is attributable to the decreasing number of cycles displayed. The data was found to form a continuous function despite the different number of cycles displayed. We conclude that the fall off in sensitivity is due to the spatial interactions in disparity processing. We also determined DSFs for the same observers to both vertically and horizontally oriented sinusoidal disparity corrugations in order to characterise the extent of the stereoscopic anisotropy In general, the best thresholds for detecting vertically oriented disparity corrugations were higher (∼4 arc sec) than for horizontally oriented corrugations (∼2 arc sec). Moreover, the functions were shifted toward the high spatial frequency end of the spectrum

Accounting Choice, Home Bias, and U.S. Investment in Non-U.S. Firms

This paper examines the relation between accounting choice and U.S. institutional investor ownership in non-U.S. firms. We predict that U.S. investors exhibit home bias in their preference for accounting methods conforming to U.S. Generally Accepted Accounting Principles (GAAP) because such methods are more familiar, reduce information processing costs, and are perceived as higher quality. We find that firms exhibiting higher levels (changes) of U.S. GAAP conformity have greater levels (changes) of U.S. institutional ownership. Lead-lag regressions suggest that increases in U.S. GAAP conformity precede increases in U.S. investment, but changes in U.S. institutional holdings do not precede changes in accounting methods. We also find that the positive relation between U.S. GAAP conformity and U.S. investment holds regardless of a firm\u27s visibility to U.S. investors (e.g., American Depositary Receipt listing, stock index membership, analyst following, firm size). However, we find that U.S. GAAP conformity has a significantly greater impact among firms already visible to U.S. investors

EXPLOSIVE AND REACTIVE HORIZONTAL JUMP ASSESSMENT – RELIABILITY AND VALIDITY FOR ATHLETIC POPULATIONS

The reliability and validity of horizontal jump (HJ) kinetic measures was assessed for six female national-class track sprinters aged 15-18 years. Each sprinter performed three 10 m sprints, as well as five standing HJs and five reactive HJs from a 45 cm drop. Two Kistler force platforms (1000 Hz) covered with Mondo track surface recorded the HJ ground contact kinetics and an aluminium measuring tape was used to record HJ distance. Statistical measures included the intra-class coefficient and coefficient of variation to determine reliability of the measures. Linear regression analysis between sprint performance and the HJ measures was employed to assess validity. The standing explosive HJ test was revealed to be valid and reliable in female junior sprinters. The kinetic measures were superior to traditional field measures of jump distance

The Dynamic Evolution of Solar Wind Streams Following Interchange Reconnection

Interchange reconnection is thought to play an important role in determining the dynamics and material composition of the slow solar wind that originates from near coronal hole boundaries. To explore the implications of this process we simulate the dynamic evolution of a solar wind stream along a newly-opened magnetic flux tube. The initial condition is composed of a piecewise continuous dynamic equilibrium in which the regions above and below the reconnection site are extracted from steady-state solutions along open and closed field lines. The initial discontinuity at the reconnection site is highly unstable and evolves as a Riemann problem, decomposing into an outward-propagating shock and inward-propagating rarefaction that eventually develop into a classic N-wave configuration. This configuration ultimately propagates into the heliosphere as a coherent structure and the entire system eventually settles to a quasi-steady wind solution. In addition to simulating the fluid evolution we also calculate the time-dependent non-equilibrium ionization of oxygen in real time in order to construct in situ diagnostics of the conditions near the reconnection site. This idealized description of the plasma dynamics along a newly-opened magnetic field line provides a baseline for predicting and interpreting the implications of interchange reconnection for the slow solar wind. Notably, the density and velocity within the expanding N-wave are generally enhanced over the ambient wind, as is the O7+/O6+ ionization ratio, which exhibits a discontinuity across the reconnection site that is transported by the flow and arrives later than the propagating N-wave

INTRA-LIMB VARIABILITY AND INTER-LIMB ASYMMETRY IN GYMNASTICS JUMP TESTS

The inter-limb symmetry of loading patterns during drop landings and the first contact of rebound jumps was examined in young, talent-selected female gymnasts. Each gymnast performed three trials of each task from two box heights (72 and 107 cm) onto two Kistler force platforms. A symmetry index and coefficient of variation was calculated from the peak ground reaction forces. The loading patterns for each gymnast was categorised as either symmetrical, significant asymmetry or inconclusive asymmetry. Landing forces increased with age for the 107cm landing task. Approximately 40-45% of gymnasts displayed inter-limb asymmetry across both tasks and heights. Low incidences (12-17%) of inconclusive asymmetry were observed, where the asymmetry observed was less than the intra-limb loading variability

Juvenile southern elephant seals exhibit seasonal differences in energetic requirements and use of lipids and protein stores

Growing juvenile animals undergo many morphological, physiological, and behavioural changes that influence their energetic requirements, patterns of energy use, and ultimately, their survival and reproductive success. We examined changes in mass loss and body composition of juvenile southern elephant seals (1- and 2-yr-olds) during their two annual haul-outs. At the start and end of the midyear and molt haul-outs, we caught, weighed, and measured 41 and 14 seals, respectively. We measured blubber depth using ultrasound to estimate body composition ( lean and adipose tissue mass). Using energy densities of the adipose and lean tissue, we calculated total, lean, and adipose mass changes and energy expenditure. While molting, juvenile seals used more energy than during the midyear, which is related to the increased use of lean tissue for hair and skin regeneration. The amount of energy used increases with mass as individuals mature. We found sexual differences in energy use where females retained greater fat reserves than males by utilizing more lean tissue. These differences are most likely related to haul-out function and behavior, growth, and earlier development of females toward sexual maturity

HOW SAFE ARE THE CODE OF POINTS LANDING TECHNICAL REQUIREMENTS IN ARTISTIC GYMNASTICS? PRELIMINARY RESULTS

To examine the effect of the code of points landing technical requirements in artistic gymnastics, eight female artistic gymnasts performed backward somersault dismounts off a 90 cm vaulting box. Three dimensional motion as well as upper back accelerations were measured for three landing techniques: current competition landing with feet together (FT); competition landing with a step back (SB); landing with feet shoulder width apart (FA). Group average impact forces were lowest for the FA technique; individual analyses showed SB or FA techniques were safer for 75% of gymnasts. Upper back accelerations indicating how well they could control the impact shock did not differ between the three landing techniques. The landing rule in gymnastics does have an effect on the initial and werall impact loads for backward somersault dismounts

The oral microbiome of denture wearers is influenced by natural dentition

Objectives: The composition of dental plaque has been well defined, whereas currently there is limited understanding of the composition of denture plaque and how it directly influences denture related stomatitis (DS). The aims of this study were to compare the microbiomes of denture wearers, and to understand the implications of these towards inter-kingdom and host-pathogen interactions within the oral cavity. Methods: Swab samples were obtained from 123 participants wearing either a complete or partial denture; the bacterial composition of each sample was determined using bar-coded illumina MiSeq sequencing of the bacterial hypervariable V4 region of 16S rDNA. Sequencing data processing was undertaken using QIIME, clustered in Operational Taxonomic Units (OTUs) and assigned to taxonomy. The dentures were sonicated to remove the microbial flora residing on the prosthesis, sonicate was then cultured using diagnostic colorex Candida media. Samples of unstimulated saliva were obtained and antimicrobial peptides (AMP) levels were measured by ELISA. Results: We have shown that dental and denture plaques are significantly distinct both in composition and diversity and that the oral microbiome composition of a denture wearer is variable and is influenced by the location within the mouth. Dentures and mucosa were predominantly made up of Bacilli and Actinobacteria. Moreover, the presence of natural teeth has a significant impact on the overall microbial composition, when compared to the fully edentulous. Furthermore, increasing levels of Candida spp. positively correlate with Lactobacillus spp. AMPs were quantified, though showed no specific correlations. Conclusions: This is the first study to provide a detailed understanding of the oral microbiome of denture wearers and has provided evidence that DS development is more complex than simply a candidal infection. Both fungal and bacterial kingdoms clearly play a role in defining the progression of DS, though we were unable to show a defined role for AMPs