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Fourier transform spectroscopy has found application in many areas including chemometrics, biomedical and biochemical studies, and atmospheric chemistry. This paper describes an investigation into the application of the LLNL Hyperspectral Infrared Imaging Spectrometer (HIRIS) to the non-destructive evaluation of man-made and natural materials. We begin by describing the HIRIS system and the objects studied in the investigation. Next, we describe the technique used to collect the hyperspectral imagery and discuss the processing required to transform the data into usable form. We then describe a technique to analyze the data, and provide some preliminary results.

The task related changes in the Gp I inputs were investigated in type-identified motor units in the wrist extensor muscles. During wrist extension, the monosynaptic inputs generated by applying radial nerve stimulation were distributed among the motoneurone pool in line with the size principle. Their effectiveness was enhanced in the same way during hand clenching and during wrist extension combined with stimulation of the palm and finger cutaneous receptors. The orderly distribution of the monosynaptic Gp I inputs was reversed by the presynaptic inhibition induced by stimulating the Gp I flexor afferents. The effects of the presynaptic inhibition were partially released by applying cutaneous stimulation. During wrist extension, the Gp I flexor afferents generated disynaptic excitatory inputs acting specifically on high-threshold motor units together with disynaptic inhibitory inputs distributed in line with the size principle among the wrist extensor motor nucleus. During hand lenching, their effectiveness was differentially modulated depending on the motor unit type.

The task related changes in the GpIinputs were investigated in type-identified motor units in the wrist extensor muscles. During wrist extension, the monosynaptic inputs generated by applying radial nerve stimulation were distributed among the motoneurone pool in line with the size principle. Their effectiveness was enhanced in the same way during hand clenching and during wrist extension combined with stimulation of the palm and finger cutaneous receptors. The orderly distribution of the monosynaptic Gp I inputs was reversed by the presynaptic inhibition induced by stimulating the Gp I flexor afferents. The effects of the presynaptic inhibition were partially released by applying cutaneous stimulation. During wrist extension, the Gp I flexor afferents generated disynaptic excitatory inputs acting specifically on high-threshold motor units together with disynaptic inhibitory inputs distributed in line with the size principle among the wrist extensor motor nucleus. During hand clenching, their effectiveness was differentially modulated depending on the motor unit type.

1. Inhibitory and facilitatory neuronal circuits may be explored in the human motor cortex by double pulse transcranial magnetic stimulation (TMS). At short interstimulus intervals (2-5 ms), conditioned motor-evoked potentials (MEPs) are reduced (intracortical inhibition, ICI), whereas they are facilitated at longer interstimulus intervals (8-25 ms; intracortical facilitation, ICF). The aim of this study was to investigate the effects of homonymous and antagonist nerve stimulation on the intracortical inhibition and facilitation in the cortical areas that control the wrist extensor and flexor radialis muscles. 2. Sixteen subjects were asked to contract either their wrist extensor or flexor muscles. The MEP evoked by a test TMS (at 1.2 x MEP threshold) and recorded in the target muscle was then conditioned by subthreshold TMS (at 0.8 x MEP threshold) 2 and 14 ms before the test TMS. The median and radial nerves were stimulated at 0.8 x motor threshold (MT). 3. In both flexor and extensor muscles, antagonist nerve stimulation 40 ms before the test TMS decreased ICI and increased ICF. In contrast, homonymous nerve stimulation had no effect on ICI and ICF. 4. The intensity of the antagonist nerve stimulation required to alter ICI and ICF was as low as 0.6 x MT, which suggests that thick diameter afferents may be involved. The nerve stimulation had to be applied 35-45 ms prior to the test TMS to alter significantly the intracortical excitability. 5. Cutaneous afferents were probably not responsible for the alterations of intracortical excitability, since cutaneous stimulation had no effect on either ICI or ICF at the investigated intervals. 6. The present data suggest that antagonist muscular afferent inputs may evoke reciprocal facilitation or disinhibition at the cortical level. This pattern of antagonist sensory afferent effects may be of significance for control of the wrist extensor and flexor muscles when used as synergists during manipulatory finger movements and gripping tasks.

Task-related changes in the corticospinal excitation of the right extensor carpi radialis (ECR) muscle were investigated in 16 healthy human subjects. The subjects were asked to perform a tonic isometric wrist extension or to clench their hand around a manipulandum, thereby coactivating the antagonistic wrist muscles. At matched levels of background EMG in the ECR muscle, transcranial magnetic stimulation (TMS) was applied through a figure-of-eight coil at 20–30 sites spaced 1 cm apart over the hand area of the left motor cortex. The cortical maps of the representation of the ECR muscle constructed in this way did not change between the two motor tasks. Nevertheless, for all investigated cortical sites TMS evoked a smaller motor evoked potential (MEP) in the ECR muscles during hand clenching than during wrist extension. A similar decrease in the short-latency peak in the poststimulus time histogram (PSTH) of single ECR motor units to TMS during hand clenching was found in seven subjects (number of motor units = 35). In contrast, short-latency peaks in the PSTH evoked by electrical stimulation of the motor cortex had a similar size during the two tasks (number of motor units = 9; two subjects). Already the initial 0.5–1.0 ms of the short-latency peak evoked by TMS was depressed during hand clenching, which suggests that decreased excitability of corticospinal cells with monosynaptic projections onto ECR motor units was involved. This decreased excitability was not explained by increased intracortical inhibition, which was found to be of a similar size during hand clenching and wrist extension. The task-related changes in the efficiency of the motor cortex output are discussed in relation to the function of the wrist antagonist muscles in handling and gripping tasks.

Objective: Task-dependent changes in the Ia presynaptic inhibition generated by flexor group I afferents were investigated in 25 identified motor units (MUs) located in human extensor carpi radialis (ECR) muscles. Methods: Seven subjects had to voluntarily contract their ECR muscles either alone during isometric wrist extension or concurrently with their wrist and finger flexor muscles while clenching their hand around a manipulandum. The MU reflex responses to the radial nerve stimulation (test stimulation) yielded narrow peaks in the post-stimulus time histograms (PSTH). The Ia presynaptic inhibition induced while stimulating the median nerve (conditioning stimulation) 20 and 40 ms before the radial nerve was assessed from the changes in the contents of the first 0.5 ms in the peaks. Results: With both stimulation intervals, the Ia presynaptic inhibition, as assessed from the first 0.5 ms of the PSTH peaks, was consistently weaker during hand clenching. With both motor tasks, the Ia presynaptic inhibition was strongest at the 20 ms interval, in which it showed a downward gradient, working from slow to fast contracting MUs. With both intervals, the presynaptic inhibition was consistently weaker during hand clenching. The decrease in the Ia presynaptic inhibition observed at the 40 ms conditioning-test interval was less pronounced during wrist extension. Conclusion: It is suggested that the reason why Ia presynaptic inhibition was weaker during hand clenching may have been that this task involved numerous cutaneous inputs originating from the palm and finger tips. During gripping tasks, these cutaneous inputs may therefore contribute to adjusting the wrist stiffness by relieving the presynaptic inhibition.

Presynaptic inhibition is itself inhibited by input from cutaneous afferents, as clearly demonstrated in animal experiments (see Rudomin, 1990). In humans, most previous studies dealing with the effects of cutaneous afferents on the magnitude of Ia presynaptic inhibition have involved applying electrical stimulation to the superficial cutaneous nerves. Inhibitory effects of cutaneous afferents on Ia presynaptic inhibition have been observed in both leg (Iles & Roberts, 1987; Iles, 1996) and forearm muscles (Berardelli et al. 1987; Nakashima et al. 1990), based on changes in the amplitude of the H reflex. Iles (1996) has tested the effects of applying mechanical stimulation to the skin of the plantar sole on the H reflex evoked in the soleus muscle in two subjects. Mechanical stimulation of the low threshold cutaneous receptors was found to decrease the Ia presynaptic inhibition, as assessed by measuring the changes in the H reflex, as efficiently as electrical stimulation. The aim of the present study was to investigate the possibility that the numerous cutaneous inputs arising on the palmar side of the hand during manipulatory movements may selectively modulate the proprioceptive assistance to the wrist myotatic unit by altering the Ia presynaptic inhibition. In order to activate low threshold cutaneous receptors, the skin of the palm and the fingertips was continuously swept with a soft rotating brush, using a procedure based on microneurographic recordings of human sensory afferents (Ribot-Ciscar et al. 1989). The effects of the cutaneous inputs on the presynaptic inhibition elicited by stimulating the median nerve were assessed from the changes in the reflex responses of single motor units evoked by stimulating the radial nerve. The motor units were identified on the basis of their biomechanical and electrical properties (see Aimonetti et al. 2000) The main result to emerge from the present study was that the cutaneous inputs activated by the brush were liable to reduce the Ia presynaptic inhibition exerted on the responses of the wrist extensor motor units to the radial nerve stimulation. Without affecting the motoneurone excitatory drive, the cutaneous inputs were consistently found to have inhibitory effects on the Ia presynaptic inhibition in a very similar way in all the types of motor units tested. Part of this study has been previously published in abstract form (Aimonetti et al. 1997).

The question was addressed as to whether the magnitude of Ia presynaptic inhibition might depend on the type of motor unit activated during voluntary contraction in the wrist extensor muscles. For this purpose, we investigated the effects of applying electrical stimulation to the median nerve on the responses of 25 identified motor units to radial nerve stimulation delivered 20 ms after a conditioning stimulation. The reflex responses of the motor units yielded peaks in the post-stimulus time histograms with latencies compatible with monosynaptic activation. Although median nerve stimulation did not affect the motoneurone net excitatory drive assessed from the mean duration of the inter-spike interval, it led to a decrease in the contents of the first two 0.25 ms bins of the peak. This decrease may be consistent with the Ia presynaptic inhibition known to occur under these stimulation conditions. In the trials in which the median nerve was being stimulated, the finding that the response probability of the motor units, even in their monosynaptic components, tended to increase as their force threshold and their macro-potential area increased and as their twitch contraction time decreased suggests that the median nerve stimulation may have altered the efficiency with which the Ia inputs recruited the motoneurones in the pool. These effects were consistently observed in seven pairs of motor units each consisting of one slow and one fast contracting motor unit which were simultaneously tested, which suggests that the magnitude of the Ia presynaptic inhibition may depend on the type of motor unit tested rather than on the motoneurone pool excitatory drive. The present data suggest for the first time that in humans, the Ia presynaptic inhibition may show an upward gradient working from fast to slow contracting motor units which is able to compensate for the downward gradient in monosynaptic reflex excitation from ‘slow’ to ‘fast’ motor units. From a functional point of view, a weaker Ia presynaptic inhibition acting on the fast contracting motor units may contribute to improving the proprioceptive assistance to the wrist myotatic unit when the contraction force has to be increased.

This report details a system which fuses information contained in registered images from multiple sensors to reduce the effects of clutter and improve the ability to detect surface and buried land mines. The sensor suite currently consists of a camera that acquires images in six bands (400nm, 500nm, 600nm, 700nm, 800nm and 900nm). Past research has shown that it is extremely difficult to distinguish land mines from background clutter in images obtained from a single sensor. It is hypothesized, however, that information fused from a suite of various sensors is likely to provide better detection reliability, because the suite of sensors detects a variety of physical properties that are more separable in feature space. The materials surrounding the mines can include natural materials (soil, rocks, foliage, water, etc.) and some artifacts.

LLNL is developing an ultra-wideband, side-looking, ground- penetrating impulse radar system that can be mounted on an airborne platform for the purpose of locating buried mines. The radar system is presently mounted on an 18-meter boom. We have successfully imaged a minefield located at the Nevada Test Site. The minefield consists of real and surrogate mines of various materials and sizes placed in natural vegetation. Some areas have been cleared for noncluttered studies. A technical description of the system will be presented, describing the wideband antennas, the video pulser, the receiver hardware, and the data acquisition system. The receiver and data acquisition hardware are off-the- shelf components. The data was processed using LLLNL-developed image reconstruction software, and has been registered against the ground truth data. Images showing clearly visible mines, surface reference markers, and ground clutter will be presented.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We describe domain decomposition techniques as applied to efficient multidimensional electromagnetic particle simulation of complex physical systems. Results from two major production codes, ARGUS and CONDOR, are presented.