40 research outputs found
Motor crosslinking augments elasticity in active nematics
In active materials, uncoordinated internal stresses lead to emergent
long-range flows. An understanding of how the behavior of active materials
depends on mesoscopic (hydrodynamic) parameters is developing, but there
remains a gap in knowledge concerning how hydrodynamic parameters depend on the
properties of microscopic elements. In this work, we combine experiments and
multiscale modeling to relate the structure and dynamics of active nematics
composed of biopolymer filaments and molecular motors to their microscopic
properties, in particular motor processivity, speed, and valency. We show that
crosslinking of filaments by both motors and passive crosslinkers not only
augments the contributions to nematic elasticity from excluded volume effects
but dominates them. By altering motor kinetics we show that a competition
between motor speed and crosslinking results in a nonmonotonic dependence of
nematic flow on motor speed. By modulating passive filament crosslinking we
show that energy transfer into nematic flow is in large part dictated by
crosslinking. Thus motor proteins both generate activity and contribute to
nematic elasticity. Our results provide new insights for rationally engineering
active materials
Structuring Stress for Active Materials Control
Active materials are capable of converting free energy into mechanical work
to produce autonomous motion, and exhibit striking collective dynamics that
biology relies on for essential functions. Controlling those dynamics and
transport in synthetic systems has been particularly challenging. Here, we
introduce the concept of spatially structured activity as a means to control
and manipulate transport in active nematic liquid crystals consisting of actin
filaments and light-sensitive myosin motors. Simulations and experiments are
used to demonstrate that topological defects can be generated at will, and then
constrained to move along specified trajectories, by inducing local stresses in
an otherwise passive material. These results provide a foundation for design of
autonomous and reconfigurable microfluidic systems where transport is
controlled by modulating activity with light
Determining spatial and temporal scales for management: lessons from whaling
Selection of the appropriate management unit is critical to the conservation of animal populations. Defining such units depends upon knowledge of population structure and upon the timescale being considered. Here, we examine the trajectory of eleven subpopulations of five species of baleen whales to investigate temporal and spatial scales in management. These subpopulations were all extirpated by commercial whaling, and no recovery or repopulation has occurred since. In these cases, time elapsed since commercial extinction ranges from four decades to almost four centuries. We propose that these subpopulations did not recover either because cultural memory of the habitat has been lost, because widespread whaling among adjacent stocks eliminated these as sources for repopulation, and/or because segregation following exploitation produced the abandonment of certain areas. Spatial scales associated with the extirpated subpopulations are frequently smaller than those typically employed in management. Overall, the evidence indicates that: (1) the time frame for management should be at most decadal in scope (i.e., \u3c100 yr) and based on both genetic and nongenetic evidence of population substructure, and (2) at least some stocks should be defined on a smaller spatial scale than they currently are
Reversing the Balance Wheel Principle
The paper discusses funding principles and policies of higher education during the recession period. The role of state appropriations for the viability of public higher education institutions is emphasized. State funding affecting institutional behaviour is another issue raised. The paper analyzes the possibility of expanding state funding for higher education institutions instead of cutting during economic recession. The examples of Midwestern states is discussed for this purpose. Funding higher education institutions is perceived as an important component of the process of investing in human capital. Referring to scholarly findings, Leader-Laggard Model and Event History Analysis are suggested as optimal methods for evaluating the implementation of new policies as they spread from one state to another
Higher Education Funding Issues: U.S. / UK Comparison
The paper compares and contrasts higher education funding sources and systems in the U.S. and the UK. The issues raised in the paper pertain to the major challenge of academia: finding financial support in times of limited resources and enhanced competition. The issues discussed throughout the paper are: funding and quality assessment of universities; funding and equity of access to post-secondary education; marketization and privatization of universities; funding, autonomy and accountability of higher education institutions
TERMS IN THE FIRE SAFETY REGULATORY DOCUMENTS. BUILDINGS AND STRUCTURES
The article discusses the most commonly used (applied) terms in normative legal acts and regulatory documents related to fire safety of buildings and structures. Misinterpretation of terms leads to distortion (wrong selection) of fire safety requirements. The proposals to change the definitions of some terms and several paragraphs of the Technical regulations for fire safety requirements as well as Codes of rules are stated