Determination of density and concentration from fluorescent images of a gas flow

A fluorescent image analysis procedure to determine the distribution of species concentration and density in a gas flow is proposed. The fluorescent emission is due to the excitation of atoms/molecules of a gas that is intercepted by an electron blade. The intensity of the fluorescent light is proportional to the local number density of the gas. When the gas flow is a mixture of different species, this proportionality can be exploited to extract the contribution associated to the species from the spectral superposition acquired by a digital camera. This yields a method that simultaneously reveals species concentrations and mass density of the mixture. The procedure is applied to two under-expanded sonic jets discharged into a different gas ambient - Helium into Argon and Argon into Helium - to measure the concentration and density distribution along the jet axis and across it. A comparison with experimental and numerical results obtained by other authors when observing under-expanded jets at different Mach numbers is made with the density distribution along the axis of the jet. This density distribution appears to be self-similar.Comment: New figures in portable .eps forma

Principles of sensorimotor learning.

The exploits of Martina Navratilova and Roger Federer represent the pinnacle of motor learning. However, when considering the range and complexity of the processes that are involved in motor learning, even the mere mortals among us exhibit abilities that are impressive. We exercise these abilities when taking up new activities - whether it is snowboarding or ballroom dancing - but also engage in substantial motor learning on a daily basis as we adapt to changes in our environment, manipulate new objects and refine existing skills. Here we review recent research in human motor learning with an emphasis on the computational mechanisms that are involved

Immediate changes in feedforward postural adjustments following voluntary motor training

There is limited evidence that preprogrammed feedforward adjustments, which are modified in people with neurological and musculoskeletal conditions, can be trained and whether this depends on the type of training. As previous findings demonstrate consistent delays in feedforward activation of the deep abdominal muscle, transversus abdominis (TrA), in people with recurrent low back pain (LBP), we investigated whether training involving voluntary muscle activation can change feedforward mechanisms, and whether this depends on the manner in which the muscle is trained. Twenty-two volunteers with recurrent LBP were randomly assigned to undertake either training of isolated voluntary activation of TrA or sit-up training to activate TrA in a non-isolated manner to identical amplitude. Subjects performed a trunk perturbation task involving arm movement prior to and after training, and surface and fine-wire electromyography (EMG) recordings were made from trunk and arm muscles. Following a single session of training of isolated voluntary activation of TrA, onset of TrA EMG was earlier during rapid arm flexion and extension, to more closely resemble the responses in pain-free individuals. The magnitude of change in TrA EMG onset was correlated with the quality of isolated training. In contrast, all of the abdominal muscles were recruited earlier during arm flexion after sit-up training, while onset of TrA EMG was further delayed during arm extension. The results provide evidence that training of isolated muscle activation leads to changes in feedforward postural strategies, and the magnitude of the effect is dependent on the type and quality of motor training

Virtual reality for sensorimotor rehabilitation post stroke: design principles and evidence

n the recent years, the use of virtual reality (VR) to enhance motor skills of persons with activity and participation restriction due to disease or injury has been become an important area of research. In this chapter, we describe the design of such VR systems and their underlying principles, such as experience-dependent neuroplasticity and motor learning. Further, psychological constructs related to motivation including salience, goal setting, and rewards are commonly utilized in VR to optimize motivation during rehabilitation activities. Hence, virtually simulated activities are considered to be ideal for (1) the delivery of specifi c feedback, (2) the a bility to perform large volumes of training, and (3) the presentation of precisely calibrated diffi culty levels, which maintain a high level of challenge throughout long training sessions. These underlying principles are contrasted with a growing body of research comparing the effi cacy of VR with traditionally presented rehabilitation activities in persons with stroke that demonstrate comparable or better outcomes for VR. In addition, a small body of literature has utilized direct assays of neuroplasticity to evaluate the effects of virtual rehabilitation interventions in persons with stroke. Promising developments and fi ndings also arise from the use of off-the-s helf video game systems for virtual rehabilitation purposes and the integration of VR with robots and brain-computer interfaces. Several challenges limiting the translation of virtual rehabilitation into routine rehabilitation practice need to be addressed but the fi eld continues to hold promise to answer key issues faced by modern healthcare.info:eu-repo/semantics/publishedVersio