Slow and Steady Method for Advancing Devices Through Tight or Tortuous Anatomy

Advancing vascular sheaths, catheters, balloons, stent grafts, or drainage catheters can prove difficult in tight or tortuous anatomy, leading to prolonged procedure and fluoroscopy time. Overcoming the static forces of friction requires greater magnitude of force compared to the kinetic forces of friction. Static forces of friction can result in catheter or device kinking, particularly in tight or tortuous anatomy. By applying slow, steady force (as opposed to multiple isolated applications of force) in a manner described in this chapter, one can advance a device in a slow and steady manner, thus reducing the amount of pain, tissue damage, and potentially fluoroscopy time.

Prediction of residual clamping force for Coulomb type and Johnsen–Rahbek type of bipolar electrostatic chucks

As a key component in semiconductor manufacturing equipment, electrostatic chuck is conventionally divided into Coulomb type and J–R type depending on the generating mechanism of clamping force. After supply voltage is cut off, residual clamping force usually remains and becomes a serious issue for production efficiency and process reliability. Hence, it is significant to propose a general prediction model and reveal changing laws of residual force with time for both types. This paper establishes an equivalent circuit model for a bipolar electrostatic chuck containing distributed embosses on dielectric layer surface, and deduces a unified form of mathematical expression describing decaying force, which can cover the two types. The obtained equations can also predict steady force in working state. Furthermore, an experimental method for measuring clamping force and de-clamping time is presented. The results indicate relative deviations tend to decrease as voltages rise. It is found that prediction precision for J–R type is lower than that for Coulomb type. Main reasons are explained and relevant mechanisms are discussed. Overall, the calculations coincide with the measurements within an acceptable error range. The comparisons suggest the theoretical model is effective for simulating the characteristics of residual clamping force for both types of electrostatic chucks.

Analysis of Differential Mechanisms for a Robotic Head Stabilization System

This paper presents a robotic system intended to help automate the head and neck stabilization process performed on trauma patients through application of a differential apparatus, a device that distributes an input between multiple output channels. A system to streamline the head stabilization process can save valuable time in a life and death scenario, as well as play a key role in future work on a mobile stretcher robot. This investigation focuses on finding the most suitable device to accommodate multiple possible head positions while maintaining a steady force in order to provide secure motion restriction. After an initial review of current emergency medical services standards, a comparison of potential differential mechanisms is undertaken. Static analysis as well as dynamic modeling is performed in order to determine the most appropriate mechanisms. An initial prototype design incorporating a differential pulley, the most mechanically advantageous mechanism, is then introduced.

Immigrants, Productivity, and Labor Markets

Immigration has been a steady force acting on population and employment within countries throughout human history. Focusing on the last four decades, we show that the mix of immigrants to rich countries has been, overall, rather balanced between college and non-college educated. The growth of immigration has been driven by immigrants from nonrich countries. The economic impact of immigration on receiving economies needs to be understood by analyzing the specific skills brought by immigrants. The complementarity and substitutability between immigrants and natives in employment, and the response of receiving economies in terms of specialization and technological choices, are important when considering the general equilibrium effects of immigration. In the United States, a balanced composition of immigrants between college and noncollege educated, together with the adjustment of demand and technology, imply that general equilibrium effects on relative and absolute wages have been small.

Influence of the contractile properties of muscle on motor unit firing rates during a moderate-intensity contraction in vivo

It is suggested that firing rate characteristics of motor units (MUs) are influenced by the physical properties of the muscle. However, no study has correlated MU firing rates at recruitment, targeted force, or derecruitment with the contractile properties of the muscle in vivo. Twelve participants (age = 20.67 ± 2.35 yr) performed a 40% isometric maximal voluntary contraction of the leg extensors that included linearly increasing, steady force, and decreasing segments. Muscle biopsies were collected with myosin heavy chain (MHC) content quantified, and surface electromyography (EMG) was recorded from the vastus lateralis. The EMG signal was decomposed into the firing events of single MUs. Slopes and y-intercepts were calculated for 1) firing rates at recruitment vs. recruitment threshold, 2) mean firing rates at steady force vs. recruitment threshold, and 3) firing rates at derecruitment vs. derecruitment threshold relationships for each subject. Correlations among type I %MHC isoform content and the slopes and y-intercepts from the three relationships were examined. Type I %MHC isoform content was correlated with MU firing rates at recruitment ( y-intercepts: r = −0.577; slopes: r = 0.741) and targeted force (slopes: r = 0.853) vs. recruitment threshold and MU firing rates at derecruitment ( y-intercept: r = −0.597; slopes: r = 0.701) vs. derecruitment threshold relationships. However, the majority of the individual MU firing rates vs. recruitment and derecruitment relationships were not significant ( P > 0.05) and, thus, revealed no systematic pattern. In contrast, MU firing rates during the steady force demonstrated a systematic pattern with higher firing rates for the lower- than higher-threshold MUs and were correlated with the physical properties of MUs in vivo.

Molecular Dynamics Simulation of Stick-Slip Friction on a Metal Surface

Friction on the atomistic scale was simulated using a molecular dynamics model consisting of a slider and substrate. The slider is in contact with the substrate through interatomic forces, while being pulled by a spring connected to a tractor moving parallel to the substrate surface at a constant velocity. The frictional force, which is defined as the force working on the connecting spring, is registered as the slider moves over the substrate, and consequently stick-slip behavior is observed. The static frictional force is higher if the lattice mismatch between slider and substrate is smaller. The sliding velocity affects whether atoms can rapidly settle into a stable site, and hence affects the kinetic friction; at high velocities, the atoms are forcibly moved resulting in a smaller kinetic friction force and a steady force curve.

Sensitivity analysis and passive control of cylinder flow

A general theoretical formalism is developed to assess how base-flow modifications may alter the stability properties of flows studied in a global approach of linear stability theory. It also comprises a systematic approach to the passive control of globally unstable flows by the use of small control devices. This formalism is based on a sensitivity analysis of any global eigenvalue to base-flow modifications. The base-flow modifications investigated are either arbitrary or specific ones induced by a steady force. This leads to a definition of the so-called sensitivity to base-flow modifications and sensitivity to a steady force. These sensitivity analyses are applied to the unstable global modes responsible for the onset of vortex shedding in the wake of a cylinder for Reynolds numbers in the range 47≤Re≤80. First, it is demonstrated how the sensitivity to arbitrary base-flow modifications may be used to identify regions and properties of the base flow that contribute to the onset of vortex shedding. Secondly, the sensitivity to a steady force determines the regions of the flow where a steady force acting on the base flow stabilizes the unstable global modes. Upon modelling the presence of a control device by a steady force acting on the base flow, these predictions are then extensively compared with the experimental results of Strykowski & Sreenivasan (J. Fluid Mech., vol. 218, 1990, p. 71). A physical interpretation of the suppression of vortex shedding by use of a control cylinder is proposed in the light of the sensitivity analysis.