Quantal release at visualized terminals of a crayfish motor axon: intraterminal and regional differences

Synaptic transmission was measured at visualized terminal varicosities of the motor axon providing the sole excitatory innervation of the "opener" muscle in walking legs of crayfish (Procambarus clarkii Girard). Two questions were addressed: 1) How uniform is quantal emission at different locations along terminals innervating a single muscle fiber, and 2) can differences in quantal emission account for the different excitatory postsynaptic potential (EPSP) amplitudes generated by terminals localized in defined regions of the muscle? Extracellular "macropatch" electrodes were placed over individual varicosities, viewed after brief exposure to a fluorescent dye, and synaptic currents were recorded to determine quantal content of transmission. Along terminals supplying a single muscle fiber, nonuniform release was found: Varicosities closer to the point of origin of the terminal branch released more transmitter than those located more distally. Quantal content was higher for varicosities of the muscle's proximal region (where large EPSPs occur) than for varicosities of the central region (where small EPSPs occur). The probability of transmitter release per synapse is estimated to be greater for the proximal varicosities. At low frequencies of stimulation, quantal content per muscle fiber is two to four times larger in the proximal region. Taken in conjunction with a twofold higher mean input resistance for the proximal muscle fibers, the difference in quantal content can account for a four- to eightfold difference in EPSP amplitude. The observed mean EPSP amplitude is at least eight times larger in the proximal region. We discuss factors contributing to differences in EPSP amplitudes.     

The formation and evolution of the Society of Nuclear Medicine

The Society of Nuclear Medicine was created and constructed by persons from many branches of medicine and the physical sciences, but it originated mostly in the mind of a chemist-physicist-engineer named Norman "Jeff" Holter. Because most medical organizations seemed to care little about the use of radioactive materials for medical purposes, Holter believed a new organization was necessary for their promotion. From its origin in 1954 as the Pacific Northwest Society of Nuclear Medicine, The Society of Nuclear Medicine became a national, multidisciplinary organization in 1956. Rapidly gathering strength with an expanding membership, it employed an administrator in 1959. With this administrator and a dedicated volunteer editor, publication of the Journal of Nuclear Medicine began. Over the next several years the Society evolved into an active force in the development of the application of radioactivity to medical applications. It generated significant internal initiatives and participated in the generation of several important external institutions. The Society of Nuclear Medicine developed a tradition of annual meetings with strong educational programs for all members. By nurturing and embracing the Technologist Section, the Society became a robust and representative organization for all who serve nuclear medicine. From these beginnings came the vigorous Society of Nuclear Medicine of today. Jeff Holter (1914-1983) would be justifiably proud.     

Temporary bond—debond technology for high‐performance transistors on flexible substrates

Abstract— A processing technology based upon a temporary bond—debond approach has been developed that enables direct fabrication of high‐performance electronic devices on flexible substrates. This technique facilitates processing of flexible plastic and metal‐foil substrates through automated standard semiconductor and flat‐panel tool sets without tool modification. The key to processing with these tool sets is rigidifying the flexible substrates through temporary bonding to carriers that can be handled in a similar manner as silicon wafers or glass substrates in conventional electronics manufacturing. To demonstrate the power of this processing technology, amorphous‐silicon thin‐film‐transistor (a‐Si:H TFT) backplanes designed for electrophoretic displays (EPDs) were fabricated using a low‐temperature process (180°C) on bonded‐plastic and metal‐foil substrates. The electrical characteristics of the TFTs fabricated on flexible substrates are found to be consistent with those processed with identical conditions on rigid silicon wafers. These TFTs on plastic exhibit a field‐effect mobility of 0.77 cm²/V‐sec, on/off current ratio >10⁹ at Vds = 10 V, sub‐threshold swing of 365 mV/dec, threshold voltage of 0.49 V, and leakage current lower than 2 pA/μm gate width. After full TFT‐array fabrication on the bonded substrate and subsequent debonding, the flexible substrate retains its original flexibility; this enables bending of the EPD display without loss in performance.     

A Monte Carlo Simulation approach for the modeling of free-molecule squeeze-film damping of flexible microresonators

Squeeze-film damping on microresonators is a significant damping source even when the surrounding gas is highly rarefied. This article presents a general modeling approach based on Monte Carlo (MC) simulations for the prediction of squeeze-film damping on resonators in the free-molecule regime. The generality of the approach is demonstrated in its capability of simulating resonators of any shape and with any accommodation coefficient. The approach is validated using both the analytical results of the free-space damping and the experimental data of the squeeze-film damping on a clamped–clamped plate resonator oscillating at its first flexure mode. The effect of oscillation modes on the quality factor of the resonator has also been studied and semi-analytical approximate models for the squeeze-film damping with diffuse collisions have been developed.     

Application of the Strain Index in multiple task jobs

Six different methods to calculate the Strain Index (SI) scores for jobs with multiple forces/tasks were developed. Exposure data of 733 subjects from 12 different worksites were used to calculate these SI scores. Results show that using different SI computation methods could result in different SI scores, hence different risk level classifications. However, some simpler methods generated SI scores were comparable to the more complicated composite SI method. Despite differences in the scores between the six different SI computation methods, Spearman rank-order correlation coefficients of 0.61-0.97 were found between the methods. With some confidence, ergonomic practitioners may use simpler methods, depending on their specificity requirement in job evaluations and available resources. Some SI computation methods may tend to over-estimate job risk levels, while others may tend to under-estimate job risk levels, due to different ways used in obtaining the various SI parameters and computations.     

Robust resource allocation in a cluster based imaging system

Recently there has been an increased demand for imaging systems in support of high-speed digital printing. The required increase in performance in support of such systems can be accomplished through an effective parallel execution of image processing applications in a distributed cluster computing environment. The output of the system must be presented to a raster based display at regular intervals, effectively establishing a hard deadline for the production of each image. Failure to complete a rasterization task before its deadline will result in an interruption of service that is unacceptable. The goal of this research was to derive a metric for measuring robustness in this environment and to design a resource allocation heuristic capable of completing each rasterization task before its assigned deadline, thus, preventing any service interruptions. We present a mathematical model of such a cluster based raster imaging system, derive a robustness metric for evaluating heuristics in this environment, and demonstrate using the metric to make resource allocation decisions. The heuristics are evaluated within a simulation of the studied raster imaging system. We clearly demonstrate the effectiveness of the heuristics by comparing their results with the results of a resource allocation heuristic commonly used in this type of system.     

An intelligent terrain-based navigation system for planetary rovers

A fuzzy logic framework for onboard terrain analysis and guidance towards traversable regions. An onboard terrain-based navigation system for mobile robots operating on natural terrain is presented. This system utilizes a fuzzy-logic framework for onboard analysis of the terrain and develops a set of fuzzy navigation rules that guide the rover toward the safest and the most traversable regions. The overall navigation strategy deals with uncertain knowledge about the environment and uses the onboard terrain analysis to enable the rover to select easy-to-traverse paths to the goal autonomously. The navigation system is tested and validated with a set of physical rover experiments and demonstrates the autonomous capability of the system     

Two posture analysis approaches and their application in a modified rapid upper limb assessment evaluation

This paper presents two posture risk quantification methods: first, an event-based method where the most common and the worst postures are estimated in a task; second, a time-based method where posture distributions are calculated from random samples of observed postures in the task. A 'click-on-screen' posture data entry method was developed for the time-based posture analysis method to make the observation process easier and to reduce possible posture categorization bias. Both methods were used to quantify various work posture parameters among a study cohort of 733 subjects from a prospective epidemiological study of upper extremity musculoskeletal disorders. Composite posture indices using a modified Rapid Upper Limb Assessment (RULA) method were also computed using data obtained by the two posture analysis methods. Results showed that both methods were able to distinguish jobs with large differences in certain posture measures. However, they did not produce the same results and could not be used interchangeably. Risk evaluation criteria should be developed, either for specific posture parameters or as a composite index, with a well-defined postural analysis method, so that users can follow exact procedures and obtain comparable results. The event-based method is easy to use and may suit practitioners better, while the time-based method adds more information to the measurement and may suit users who want more detailed information about posture exposure.     

Flexible Image-Based Photometric Reconstruction using Virtual Light Sources

Photometric reconstruction is the process of estimating the illumination and surface reflectance properties of an environment, given a geometric model of the scene and a set of photographs of its surfaces. For mixed-reality applications, such data is required if synthetic objects are to be correctly illuminated or if synthetic light sources are to be used to re-light the scene. Current methods of estimating such data are limited in the practical situations in which they can be applied, due to the fact that the geometric and radiometric models of the scene which are provided by the user must be complete, and that the position (and in some cases, intensity) of the light sources must also be specified a-priori. In this paper, a novel algorithm is presented which overcomes these constraints, and allows photometric data to be reconstructed in less restricted situations. This is achieved through the use of virtual light sources which mimic the effect of direct illumination from unknown luminaires, and indirect illumination reflected off unknown geometry. The intensity of these virtual light sources and the surface material properties are estimated using an iterative algorithm which attempts to match calculated radiance values to those observed in photographs. Results are presented for both synthetic and real scenes that show the quality of the reconstructed data and its use in off-line mixed-reality applications.