Curvature and torsion in growing actin networks

Intracellular pathogens such as Listeria monocytogenes and Rickettsia rickettsii move within a host cell by polymerizing a comet-tail of actin fibers that ultimately pushes the cell forward. This dense network of cross-linked actin polymers typically exhibits a striking curvature that causes bacteria to move in gently looping paths. Theoretically, tail curvature has been linked to details of motility by considering force and torque balances from a finite number of polymerizing filaments. Here we track beads coated with a prokaryotic activator of actin polymerization in three dimensions to directly quantify the curvature and torsion of bead motility paths. We find that bead paths are more likely to have low rather than high curvature at any given time. Furthermore, path curvature changes very slowly in time, with an autocorrelation decay time of 200 seconds. Paths with a small radius of curvature, therefore, remain so for an extended period resulting in loops when confined to two dimensions. When allowed to explore a 3D space, path loops are less evident. Finally, we quantify the torsion in the bead paths and show that beads do not exhibit a significant left- or right-handed bias to their motion in 3D. These results suggest that paths of actin-propelled objects may be attributed to slow changes in curvature rather than a fixed torque

Weldability evaluation of thick sections of Hastelloy X with varying aluminum content. NERVA program

Weldability evaluation of thick sections of Hastelloy X with varying aluminum content, for NERVA nozzle

Prevention of rust in the ID weld and heat affected zone of CRES 347 NERVA lines. NERVA program

Rust prevention in stainless steel fluid transmission lines of nuclear engine for rocket vehicle

Beyond the Organizing Model: The Transformation Process in Local Unions

[Excerpt] The ideological foundations of traditional U.S. trade unionism have been called into question by world and domestic events. The post-World War II labor movement, founded on a social truce with capital and the apparent inevitability of a rising living standard, has hit a bulkhead-piercing iceberg of dramatic proportions. The global economy, economic restructuring, deregulation, and privatization have wrought destruction on U.S. unions. In the wake of this devastation, it has become common, even for union leaders, to define unionism in objectively negative terms (e.g., without a union, you have no protection from arbitrary management). As a movement, we have offered little in the way of a comprehensive explanation of what we stand for. The upheaval has forced new questions and problems to the surface and has set the stage for an internal debate about the future. The dialogue has included little that is fundamentally new. There have always been disagreements over labor strategy and tactics, the relationship of unions to capital, and the appropriate form of organization for the labor movement. This debate has taken on new urgency since the mid-1980s, however, and has concentrated on whether there is a viable alternative to the prevailing form of business unionism, which appears to be leading workers nowhere

Overcoming Obstacles to Transformation: Challenges on the Way to a New Unionism

[Excerpt] The change to organizing requires more than a shift in resources. It is difficult to imagine a sustained commitment to organizing at the grass roots unless locals have the tools, skills, and strategic perspective necessary to mount successful organizing campaigns. Ultimately the commitment to building the labor movement inherent in the organizing priority challenges unions to alter organizational cultures that are often deeply imbued with traditional and conservative approaches to trade unionism. The struggle to succeed at organizing, to maintain representation, and to alter union culture is forcing national unions to define their role in this process and to reassess their relationships with locals. A key objective of the research reported here is to help clarify the issues at stake in the process of the change to organizing at the local level. Although there are few definitive answers, the experiences of locals struggling with the realities of juggling organizing and representational responsibilities should guide the search for sustainable conversion

Heat flow calorimeter

Heat flow calorimeter devices are used to measure heat liberated from or absorbed by an object. This device is capable of measuring the thermal output of sealed nickel-cadmium batteries or cells during charge-discharge cycles. An elongated metal heat conducting rod is coupled between the calorimeter vessel and a heat sink, thus providing the only heat exchange path from the calorimeter vessel itself

Interaction of an Eulerian flue gas plume with wind turbines

The reduced availability of sites with the requisite wind resource, planning permission and public acceptance for the placement of wind turbines poses a significant challenge to future expansion of the wind energy industry. Developers increasingly wish to site large turbines in close proximity to industrial plants, but there is uncertainty amongst environmental protection agencies on how best to measure and regulate the impact that wind turbines may have on the dispersion of the gases that are often emitted into the atmosphere from such plants. Several simplified wind turbine-flue stack configurations have been simulated using the Vorticity Transport Model. This model provides a high-fidelity representation of the vortical flow structure within both the wind turbine wake and the plume, and is able to capture the re-direction and dispersion of the plume that occurs due to interaction with the wind turbine. The impingement of the plume on the wind turbine is shown to disrupt the wake structure downwind of the wind turbine, and may induce additional unsteady loading on the turbine rotor. The velocity deficit downwind of the wind turbine influences the rate at which the plume propagates downwind, and results in an increase in the concentration of plume material (which may include pollutant gas and particulates) around the wind turbine. This localized increase in plume concentration is shown to be sensitive to the thrust coefficient at which the wind turbine is operated. The results presented in this paper show that environmental protection agencies are justified in their concerns regarding the placement of wind turbines near to industrial plants, and suggests strongly that the interaction between wind turbines and gas plumes should be investigated further

Sense of agency, associative learning, and schizotypy

Despite the fact that the role of learning is recognised in empirical and theoretical work on sense of agency (SoA), the nature of this learning has, rather surprisingly, received little attention. In the present study we consider the contribution of associative mechanisms to SoA. SoA can be measured quantitatively as a temporal linkage between voluntary actions and their external effects. Using an outcome blocking procedure, it was shown that training action-outcome associations under conditions of increased surprise augmented this temporal linkage. Moreover, these effects of surprise were correlated with schizotypy scores, suggesting that individual differences in higher level experiences are related to associative learning and to its impact on SoA. These results are discussed in terms of models of SoA, and our understanding of disrupted SoA in certain disorders

Annoyance resulting from intrusion of aircraft sounds upon various activities

An experiment was conducted in which subjects were engaged in TV viewing, telephone listening, or reverie (no activity) for a 1/2-hour session. During the session, they were exposed to a series of recorded aircraft sounds at the rate of one flight every 2 minutes. Within each session, four levels of flyover noise, separated by dB increments, were presented several times in a Latin Square balanced sequence. The peak level of the noisiest flyover in any session was fixed at 95, 90, 85, 75, or 70 dBA. At the end of the test session, subjects recorded their responses to the aircraft sounds, using a bipolar scale which covered the range from very pleasant to extremely annoying. Responses to aircraft noises were found to be significantly affected by the particular activity in which the subjects were engaged. Not all subjects found the aircraft sounds to be annoying

Effects of three activities on annoyance responses to recorded flyovers

Human subjects participated in an experiment in which they were engaged in TV viewing, telephone listening, or reverie (no activity) for a 1/2-hour session. During the session, they were exposed to a series of recorded aircraft sounds at the rate of one flight every 2 minutes. At each session, four levels of flyover noise, separated by 5 db increments were presented several times in a Latin Square balanced sequence. The peak levels of the noisiest flyover in any session was fixed at 95, 90, 85, 75, or 70 db. At the end of the test session, subjects recorded their responses to the aircraft sounds, using a bipolar scale which covered the range from very pleasant to extremely annoying. Responses to aircraft noises are found to be significantly affected by the particular activity in which the subjects are engaged