Reconstruction of objects from diverging x rays

Rotation of a system consisting of a single x-ray source and a linear detector array allows rapid collection of x-ray projection data from which transaxial cross sections can be reconstructed. In this paper, we present an algorithm which makes possible rapid computerized reconstruction from such data. We describe some experiments aimed at investigating the optimal choice of some of the parameters associated with the algorithm. We report on reconstructions using our algorithm of the intact thorax of a dog and also of cross sections of the human female breast from x-ray data obtained by a computerized mammography machine.     

Modulation effects of epidural spinal cord stimulation on muscle activities during walking.

Epidural spinal cord stimulation (ESCS) combined with partial weight bearing therapy (PWBT) has been reported to facilitate recovery of functional walking for individuals after chronic incomplete spinal cord injury (ISCI). Muscle activities were analyzed in this report to examine the modulation effect of ESCS on muscle recruitment during gait training. Two ISCI individuals participated in the study and both are classified as ASIA C with low motor scores in the lower limbs. Stimulating electrodes were placed at the epidural space over T10-L2 spinal segments, along the midline in participant 1 (S1), and off-midline in participant 2 (S2). Surface electromyograms (EMGs) from leg muscles under both ESCS ON and OFF conditions recorded during treadmill gait were analyzed in time-frequency domains. ESCS application produced acute modulations in muscle activities in both participants, but the observed pattern, magnitude, and spectral content of the EMGs differed. In S1, ESCS induced a significant shift in the temporal pattern of muscle activity toward normal comparing with that when ESCS was OFF, though without eliciting noticeable change in frequency distribution between ESCS ON and OFF conditions. When ESCS was applied in S2, a modulation of EMG magnitude was observed and, consequently, improved joint kinematics during walking. In this case, a stimulation entrainment appeared in time-frequency analysis. The results suggest that ESCS activates neural structures in the dorsal aspect of the spinal cord and facilitates gait-related muscle recruitment. The exact effects of ESCS depend on the electrode placement and possibly injury history and residual functions, but in general ESCS produces a positive effect on improved walking speed, endurance, and reduced sense of effort in both ISCI subjects.     

A System for Semi-Autonomous Tractor Operations

Tractors are the workhorses of the modern farm. By automating these machines, we can increase the productivity, improve safety, and reduce costs for many agricultural operations. Many researchers have tested computer-controlled machines for farming, but few have investigated the larger issues such as how humans can supervise machines and work amongst them. In this paper, we present a system for tractor automation. A human programs a task by driving the relevant routes. The task is divided into subtasks and assigned to a fleet of tractors that drive portions of the routes. Each tractor uses on-board sensors to detect people, animals, and other vehicles in the path of the machine, stopping for such obstacles until it receives advice from a supervisor over a wireless link. A first version of the system was implemented on a single tractor. Several features of the system were validated, including accurate path tracking, the detection of obstacles based on both geometric and non-geometric properties, and self-monitoring to determine when human intervention is required. Additionally, the complete system was tested in a Florida orange grove, where it autonomously drove seven kilometers.     

Mental manipulation of spatial information in young and elderly adults.

Investigated the ability of 20-, 60-, and 70-yr-olds (12 men and 12 women at each age level) to mentally manipulate spatial information in a large-scale environment. In a perspective-taking task, Ss were asked to determine the location of target objects from imagined locations. In an array rotation task, Ss were asked to imagine that the array of objects rotated relative to their current position. Young and elderly Ss performed with equivalent accuracy on the array rotation task, but young Ss were more accurate on the perspective-taking task. Ss who were taken to each object location prior to testing were more accurate in the perspective-taking task than Ss who did not have this experience. There was no effect of prior experience on performance in the array rotation task. (4 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modeling of unsteady two-phase reactive flow in porous beds of propellant

A model describing reactive two-phase flow through a gas-solid mixture is presented based upon either the concept of continuum mixture or the concept of separated-flow continuum. The resulting governing equations are solved by the method of finite differences. Details of two distinct numerical methods to solve these nonlinear, coupled hyperbolic partial differential equations simultaneously are also presented. In addition, artificial smearing techniques which are generally needed for the shock capturing methods are investigated. The analysis of the transient convective mode combustion process in a highly loaded granular bed of energetic solid propellant indicates a rapidly burning pressure front and an accelerating deflagration front. During the final stages of the burn, the velocity of this deflagration front can range from 1 to 3 mm/μs. A detailed discussion is included which attempts to explain the limits of the theoretical model presented in this study. Assessments are also made regarding the validity of many of the constitutive laws utilized and the assumptions necessary for this analysis. The study concludes with assessment of the modeling effort and how such unsteady flow processes could lead to DDT (deflagration-to-detonation transition) in such porous beds.     

Adequate mothering by partially isolated rhesus monkeys after observation of maternal care.

13 laboratory-born female monkeys were allowed to remain with their mothers for about 4 mo and were subsequently singly caged in rooms where they were able to see other monkeys. Ss that did not see mothers caring for their infants neglected their own firstborn. In contrast, Ss that were allowed to observe separately caged mother–infant pairs accepted their own infants but initially held them in atypical positions. Only 2–3 yrs of natural group life, which probably involved observation of mothering and carrying younger group members, led to acceptance as well as normal holding postures. Results indicate that visual exposure to maternal care, which must take place when the animal is older than about 4 mo, leads to acceptance of the neonate. However, subsequent tactual experience is usually required for learning to hold the infant properly. (8 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ultra-rapid quenching of laser-melted binary and unary oxides

A technique has been developed for ultra-rapid quenching of oxide materials from the liquid state. A modified Duwez splat gun combined with a continuous wave 400 watt CO₂ laser achieved quench rates estimated to be ～10⁷°C/sec. Mixed non-crystalline solid (NCS) and crystalline product phases were formed for both Al₂O₃ and MgAl₂O₄, as predicted theoretically. Moreover, mixed NCS and crystalline phases were formed in the binary systems MgOAl₂O₃, Al₂O₃Y₂O₃, Al₂O₃SiO₂ and MgOCaO.