Motility-driven glass and jamming transitions in biological tissues

Cell motion inside dense tissues governs many biological processes, including embryonic development and cancer metastasis, and recent experiments suggest that these tissues exhibit collective glassy behavior. To make quantitative predictions about glass transitions in tissues, we study a self-propelled Voronoi (SPV) model that simultaneously captures polarized cell motility and multi-body cell-cell interactions in a confluent tissue, where there are no gaps between cells. We demonstrate that the model exhibits a jamming transition from a solid-like state to a fluid-like state that is controlled by three parameters: the single-cell motile speed, the persistence time of single-cell tracks, and a target shape index that characterizes the competition between cell-cell adhesion and cortical tension. In contrast to traditional particulate glasses, we are able to identify an experimentally accessible structural order parameter that specifies the entire jamming surface as a function of model parameters. We demonstrate that a continuum Soft Glassy Rheology model precisely captures this transition in the limit of small persistence times, and explain how it fails in the limit of large persistence times. These results provide a framework for understanding the collective solid-to-liquid transitions that have been observed in embryonic development and cancer progression, which may be associated with Epithelial-to-Mesenchymal transition in these tissues.Comment: accepted for publication in Physical Review X, 201

Anthropometric Characteristics of Chinese Professional Female Marathoners and Predicted Variables for their Personal Bests

To investigate anthropometric characteristic of Chinese professional female marathoners and suitable predicted variables correlated with their personal bests(PBs). During the process of talent identification for London Olympic game, 96 Chinese female long-distance runners were divided into international(<2 h 34 min), national(2 h 34min~2 h 45min) and average(2 h 45 min~3 h 19 min) levels according to their PBs in marathon. Selected anthropometric variables, including height, body mass, %body fat, girths, breadths, lengths and skin-fold thicknesses were measured. Only iliac crest skin-fold of international athletes were significantly lower than its in national group. Girth of forearm and lower limbs, length of lower limbs, and all skin-fold thicknesses of national athletes were significantly lower than those from average level group. % body fat, girth of forearm and calf, length of lower limbs, and skin-folds at sites of subscapular, abdominal and iliac crest of athletes from average level group were significantly higher than those in international athletes. Positive correlation was found between forearm girth and PBs, and between the subscapular, abdominal, iliac crest and triceps surae skin-folds and PB for total athletes. Negative correlation between biiliac breadth and PB in international athletes, and positive correlations between abdominal and triceps surae skin-folds and PBs in national athletes were found. For average runners, high positive correlation was found between upper arm girth and PBs, and between subscapular, abdominal, iliac crest and triceps surae skin-folds and PBs. The findings suggested that compared to stride length, stride frequency and efficiency were more important factors influencing running performance, which were in accordance with running technique in Chinese female marathoners

Existence of multiple positive solutions of higher order multi-point nonhomogeneous boundary value problem

In this paper, by using the Avery and Peterson fixed point theorem, we establish the existence of multiple positive solutions for the following higher order multi-point nonhomogeneous boundary value problem $u^{(n)}(t) + f(t,u(t),u'(t),\ldots,u^{(n-2)}(t)) = 0, t\in (0,1)$, $u(0)= u'(0)=\cdots=u^{(n-3)}(0)=u^{(n-2)}(0)=0, u^{(n-2)}(1)-\sum_{i=1}^{m} a_i u^{(n-2)}(\xi_i)=\lambda$, where $n\ge3$ and $m\ge1$ are integers, $00$ for $1\le i\le m$ and $\sum_{i=1}^{m} a_i\xi_i<1$, $f(t,u,u',\cdots,u^{(n-2)})\in C([0,1]\times[0,\infty)^{n-1}, [0,\infty))$. We give an example to illustrate our result

Vibration testing of a steel girder bridge using cabled and wireless sensors

Author's manuscript. The final publication is available at Springer via http://dx.doi.org/10.1007/s11709-011-0113-y© Higher Education Press and Springer-Verlag Berlin Heidelberg 2011Being able to significantly reduce system installation time and cost, wireless sensing technology has attracted much interest in the structural health monitoring (SHM) community. This paper reports the field application of a wireless sensing system on a 4-span highway bridge located in Wayne, New Jersey in the US. Bridge vibration due to traffic and ambient excitation is measured. To enhance the signal-to-noise ratio, a low-noise high-gain signal conditioning module is developed for the wireless sensing system. Nineteen wireless and nineteen cabled accelerometers are first installed along the sidewalk of two neighboring bridge spans. The performance of the wireless sensing system is compared with the high-precision cabled sensing system. In the next series of testing, sixteen wireless accelerometers are installed under the deck of another bridge span, forming a 4 × 4 array. Operating deflection analysis is successfully conducted using the wireless measurement of traffic and ambient vibrations.National Science Foundatio

Triple positive solutions for second-order four-point boundary value problem with sign changing nonlinearities

In this paper, we study the existence of triple positive solutions for second-order four-point boundary value problem with sign changing nonlinearities. We first study the associated Green's function and obtain some useful properties. Our main tool is the fixed point theorem due to Avery and Peterson. The results of this paper are new and extent previously known results

Green's function and positive solutions of a singular nth-order three-point boundary value problem on time scales

In this paper, we investigate the existence of positive solutions for a class of singular $n$th-order three-point boundary value problem. The associated Green's function for the boundary value problem is given at first, and some useful properties of the Green's function are obtained. The main tool is fixed-point index theory. The results obtained in this paper essentially improve and generalize some well-known results

Correlating Cell Shape and Cellular Stress in Motile Confluent Tissues

Collective cell migration is a highly regulated process involved in wound healing, cancer metastasis and morphogenesis. Mechanical interactions among cells provide an important regulatory mechanism to coordinate such collective motion. Using a Self-Propelled Voronoi (SPV) model that links cell mechanics to cell shape and cell motility, we formulate a generalized mechanical inference method to obtain the spatio-temporal distribution of cellular stresses from measured traction forces in motile tissues and show that such traction-based stresses match those calculated from instantaneous cell shapes. We additionally use stress information to characterize the rheological properties of the tissue. We identify a motility-induced swim stress that adds to the interaction stress to determine the global contractility or extensibility of epithelia. We further show that the temporal correlation of the interaction shear stress determines an effective viscosity of the tissue that diverges at the liquid-solid transition, suggesting the possibility of extracting rheological information directly from traction data.Comment: 12 pages, 9 figure