Spontaneous formation of chaotic protrusions in a polymerizing active gel layer

The actin cortex is a thin layer of actin filaments and myosin motors beneath the outer membrane of animal cells. It determines the cells' mechanical properties and forms important morphological structures. Physical descriptions of the cortex as a contractile active gel suggest that these structures can result from dynamic instabilities. However, in these analyses the cortex is described as a two-dimensional layer. Here, we show that the dynamics of the cortex is qualitatively different when gel fluxes in the direction perpendicular to the membrane are taken into account. In particular, an isotropic cortex is then stable for arbitrarily large active stresses. If lateral contractility exceeds vertical contractility, the system can either from protrusions with an apparently chaotic dynamics or a periodic static pattern of protrusions.Comment: 5 pages, 4 figure

Estimating the Scoring Output of National Football League Teams During a Season Using Economic Production Functions

This paper estimates a series of production functions that explain the number of points a National Football League team will score during a season based on six measures of its offensive performance. The models that are estimated are linear and Cobb-Douglas production functions, using data for each team for each season from 2000 to 2018. Additionally, separate production functions are estimated for two sub-periods to determine whether the production functions vary over time and an accuracy check is performed at the end of the paper, where each team’s actual points are compared to its predicted points for the 2018 season

Identifying Virtues and Values Through Obituary Data-Mining

Because obituaries are succinct and explicitly intended to summarize their subjects’ lives, they may be expected to include only the features that the author finds most salient but also to signal to others in the community the socially-recognized aspects of the deceased’s character. We begin by reviewing studies 1 and 2, in which obituaries were carefully read and labeled. We then report study 3, which further develops these results with a semi-automated, large-scale semantic analysis of several thousand obituaries. Geography, gender, and elite status all turn out to be associated with the virtues and values associated with the deceased

Modeling Unemployment Rates by Race and Gender: A Nonlinear Time Series Approach

This paper presents an unemployment rate model that provides insight into how the time series behavior, in terms of both the mean and volatility, of the unemployment rates of black males, white males, black females, and white females differ. Demographic differences in the unemployment rate response are likely to occur if certain demographic groups face discrimination or if different demographic groups gave differing investments in human capital, for example. In addition, there may be differences in other characteristics of the groups, such as differences in the age of distribution or in the marital status distribution. This paper develops and estimates a model to determine whether or not differences in unemployment rate volatility among demographic groups actually exist, utilizing an ARCH-class (autoregressive conditional heteroscedasticity) model. The findings suggest that conditional variance is symmetric for white females, black females, and black males, but is asymmetric for white males. In particular, the findings indicate that innovations increase the conditional volatility changes in each group's unemployment rate and have symmetric effects for all groups except white males.

An Analysis of Perceptions of Online Instruction by Department Chairs in the Field of Higher Educational Administration in the United States

The rapid global emergence of a multi-billion dollar electronic (e)-leaming industry has forced department chairs in the field of educational leadership and administration in higher education institutions across the United States to assess the value, quality, and legitimacy of online instruction. For many, the concept of online education significantly challenges deeply held pedagogical beliefs and educational values such as academic freedom, protection of intellectual property rights, academic integrity, and quality. For others, the fit of online education with existing departmental and institutional mission statements, cultures, budgets, reward systems, policies and procedures, is unclear or uncertain. In an age where technology has expanded our ability to create, transfer, and apply knowledge by factors of 100 to 1,000 every decade (Duderstadt, 2001), critics have labeled members of the traditional Academy as being slow and unresponsive to technological change and unresponsive to the demands of an increasingly diverse and technologically savvy customer base. The department chair as academic leader (Hecht, et al., 1999) is being called upon to lead his or her faculty body toward a more customer-responsive pedagogy that is either supplemented or replaced by digital technologies (Bergquist, 1992; Rowley, et al., 1998; Duderstadt, 1999; Duderstadt, 2001). The researcher\u27s intent was to assess educational administration department chairs\u27 perceptions regarding the prevalence and scope, value, quality, and legitimacy of online education, its equivalency with traditional face-to-face instruction, and whether or not they agree with its pedagogical and philosophical tenets. It was also the researcher\u27s intent to assess the perceived fit between online instruction and their departmental and institutional missions, cultures, structures, and budgets, and faculty members, and the extent to which and from whom they feel pressure to adopt online instructional innovations. Major conclusions from the study included (1) a perception by educational administration department chairs that online instruction is appropriate for educating and training students in a people-oriented, people-driven field such as educational administration, (2) a perception that online instruction is comparable in academic rigor, quality, and effectiveness to traditional face-to-face instruction (3) an acknowledgement that online education is not merely an instructional fad, but an instructional innovation that has a place in courses or degree programs deemed amenable by chairs and their faculty, (4) a perception that educational administration faculty are ready and willing to embrace online education as a valid, legitimate mode of instruction and, on average, have a moderate knowledge of and skill level in using instructional technologies, (5) a perception that while educational administration department chairs are aware of increasing student demands for online educational opportunities, most did not perceive students to show a stronger interest in completing their graduate degree programs online rather than face-to-face, (6) a perception that students, as customers, not be permitted to dictate the subject matter taught and course delivery mode, (7) an indication that they do not feel pressure from deans, vice presidents of academic affairs/provosts, accrediting bodies, employers of graduate students, and for-profit online institutions of higher education to offer online courses and degree programs, (8) the acknowledgement by department chairs that while they highly value providing faculty members with timely and adequate financial rewards, recognition, technical support, and professional development and training support, they are often unable to identify funding in support of these efforts, and (9) the perception that content-laden courses and courses not dependent upon the demonstration or learning of people-skills are most amenable to fully online or Web-facilitated delivery

Universal first-passage statistics of aging processes

Many out of equilibrium phenomena, such as diffusion-limited reactions or target search processes, are controlled by first-passage events. So far the general determination of the mean first-passage time (FPT) to a target in confinement has left aside aging processes, involved in contexts as varied as glassy dynamics, tracer diffusion in biological membranes or transport of cold atoms in optical lattices. Here we consider general non-Markovian scale-invariant processes in arbitrary dimension, displaying aging, and demonstrate that all the moments of the FPT obey universal scalings with the confining volume with non trivial exponents. Our analysis shows that a nonlinear scaling of the mean FPT with the volume is the hallmark of aging and provides a general tool to quantify its impact on first-passage kinetics in confinement