A continuation method for identification of the natural frequencies of an object using a measured response

The identification of the natural frequencies of an object using measured data is an ill-conditioned problem. A method and algorithm to solve the problem based on regularization by a continuation method is presented. The algorithm is applied to the measured response of a model aircraft, and the superiority of this method to Prony's method in the presence of noise is demonstrated.     

Speech-induced changes in corticospinal excitability

The aim of the experiments was to investigate the effects of speech on the excitability of corticospinal pathways to human hand muscles. Single transcranial magnetic stimuli were given randomly over the hand area of either the left or right motor cortex of 10 right-handed and 3 left-handed normal volunteers. Electromyographic responses were recorded in the relaxed first dorsal interosseous muscle while the subjects (a) read aloud a piece of text, (b) read silently, (c) spoke spontaneously, or (d) made sounds without speaking. The only consistent effect across subjects occurred during task a, which significantly increased the size of responses evoked in the dominant hand of all subjects, but had either no effect (8 subjects) or a smaller effect in the nondominant hand. Tasks b and d had no reliable effect, whereas task c tended to increase response size in both hands. Control measurements suggest that the effects in task a were caused by changes in cortical rather than spinal excitability. This is the first demonstration of lateralized speech effects on the excitability of cortical arm areas. The results provide a useful adjunct to other tests of cerebral dominance, using only single- rather than repetitive-pulse cortical stimulation.     

New progress on E/S pulse techniques for noncooperative targetrecognition

Experimental results obtained using the ground-plane time-domain scattering ranges are presented. An experimental demonstration of the noise-insensitivity of the E/S pulse technique is also presented     

E-pulse diagnostics of simple layered materials

The feasibility of using the E-pulse technique to diagnose changes in the properties of simple layered materials is undertaken. Numerical results for a conductor-backed lossy slab and a Salisbury screen show that changes in permittivity, conductivity and thickness can be diagnosed in the presence of white Gaussian noise.     

An integrated analysis of the progression of cell responses induced by permanent focal middle cerebral artery occlusion in the rat

Defining the chronology and severity of cell damage in an evolving lesion after ischemia is important for understanding the underlying mechanisms in the development of therapeutic intervention. In the present study, we used a combination of histological and immunocytochemical methods to evaluate cell responses from 30 min to 48 h after permanent occlusion of the middle cerebral artery (MCAO) in the rat. Specific immunocytochemical markers clearly revealed acute early responses in neurons (neurofilament protein 200), astrocytes (glial fibrillary acidic protein), and microglia/macrophages (OX-42 and ED-1) such as enlarged, convoluted neuronal processes, and disintegration of glia. Progressive topographic changes in the developing lesion, pinpointed by immunolabeling, indicated the severity and extension of the cell damage. Proliferation and hypertrophy of astrocytes and microglia around the infarct, and contralaterally, occurred 24-48 h after MCAO and coincided with mass necrosis and infiltration of neutrophils and macrophages into the core. These observations corroborate the suggestion that the inflammatory process is involved in the progression of the infarct.     

Role of afferent input in motor organization in health and disease.

In the healthy brain, there is a highly organized relationship between sensory input from one part of the body and the motor cortical output to muscles acting on that same part. This work investigates whether a change in purely sensory input have an impact on the organization of the motor cortex. In a previous study transcranial magnetic stimulation (TMS) techniques were used to probe the excitability of the motor cortex hand area. A measurement of the amplitude of the motor evoked potential (MEP) to standard single-pulse stimuli given through a focal coil was done. The excitability of two types of intracortical inhibition, SICI and LICI, was also measured using a paired-pulse TMS design. SICI is thought to be sensitive to activity in GABA/sub A/-ergic systems, whereas LICI may involve activation of GABA/sub B/-ergic systems. The work of other researchers has shown that these measures could be influenced by sensory input. Yet, all of them used electrical stimulation of peripheral nerve rather than a natural input. In order to investigate a more natural input, we delivered very low-amplitude vibration to the muscle belly of individual hand muscles through a small probe. This work explores the pattern of effects on MEPs and SICI in three different intrinsic hand muscles after vibration of each muscle in turn. In addition, the study also tested LICI with a paired-pulse TMS paradigm. In conclusion, it was seen that a period of sensory input, with or without the subject's attention, produces a specific pattern of sensory-motor reorganization in human cortex which develops quickly (after only 15 minutes) and lasts for at least 30 min. Since this produces changes in the motor cortex without requiring any active motor output, it may be a promising tool for neurorehabilitation even in patients who are unable to perform the active movements conventionally employed in therapy.     

The crystal structure of the human DNA repair endonuclease HAP1 suggests the recognition of extra-helical deoxyribose at DNA abasic sites

The structure of the major human apurinic/ apyrimidinic endonuclease (HAP1) has been solved at 2.2 A resolution. The enzyme consists of two symmetrically related domains of similar topology and has significant structural similarity to both bovine DNase I and its Escherichia coli homologue exonuclease III (EXOIII). A structural comparison of these enzymes reveals three loop regions specific to HAP1 and EXOIII. These loop regions apparently act in DNA abasic site (AP) recognition and cleavage since DNase I, which lacks these loops, correspondingly lacks AP site specificity. The HAP1 structure furthermore suggests a mechanism for AP site binding which involves the recognition of the deoxyribose moiety in an extrahelical conformation, rather than a 'flipped-out' base opposite the AP site.     

Model studies of mass-flow bunkers II. Velocity distributions in the discharge of solids from mass-flow bunkers

The velocities of granular solids in a mass-flow bunker have been derived from a series of uninterrupted passages of a miniature radio pill transmitter which followed closely the solids flow lines. The increased accuracy inherent in this technique, as compared with more usual “stopped flow” observations, has confirmed the presence of a dynamic arch in the upper region of the hopper, corresponding to the surface of initial acceleration of the solids. However, below the dynamic arch the solids velocity does not remain constant until the free-fall arch near the outlet from the hopper is attained, as assumed earlier; the velocity increases towards the outlet, and at any height in the hopper decreases towards the wall.A velocity discontinuity observed near the axis of the hopper suggests that the assumption that the stress distribution converges to a radial stress distribution near the outlet can only be valid for less than 3% of the solids in the hopper.     

The transformation on annealing of the metastable electrodeposit,NiSnx, to its equilibrium phases

Under slow heating conditions hot-stage transmission electron microscopy has shown that the metastable single-phase intermetallic alloy electrodeposit NiSn₀.64 to 1.04, transforms to the equilibrium phases, Ni₃Sn₂ and Ni₃Sn₄, or Ni₃Sn₂ alone, depending upon its composition. The nature of the transformation depends upon whether the product is the two-phase mixture or the single phase, but is independent of the heating rate when only Ni₃Sn₂ is formed. However at fast heating rates direct transformation to Ni₃Sn₂/Ni₃Sn₄ does not occur. Instead a further metastable phase is formed first with structure and lattice parameters corresponding to a composition extension of the Ni₃Sn₂ phase. Calorimetry studies have enabled the activation energy of the transformation to be determined for slow heating conditions. Values of 0.76 and 0.96 ev have been measured for the formation of single-phase Ni₃Sn₂ and the Ni₃Sn₂/Ni₃Sn₄ phase mixture respectively. In addition a hitherto undetected composition-independent exothermic reaction at 200° has been interpreted in terms of local atomic rearrangements in grain boundaries.     

Storage and behavior of As, Sb, Pb, and Cu in ombrotrophic peat bogs under contrasting water table conditions

Concentration depth profiles and inventories of solid-phase As, Sb, Pb, and Cu were determined in 21?Pb-dated cores from an ombrotrophic peat bog in northwest England. Cores were collected from the peat dome and adjacent to an eroding gully. Down-core distributions of As, Sb, Pb, and Cu in the dome core are almost identical. The water table is close to the dome surface with only short-term draw-down. Under these conditions, As, Sb, Pb, and Cu are immobile, allowing the reconstruction of trends in historical contaminant deposition. The peak in atmospheric deposition of As, Sb, Pb, and Cu (4.59, 2.78, 147, and 26.7 mg m?2 y?1, respectively) occurred during the late 19th century. Stable Pb isotope ratios reveal that Pb deposition during this period was from indigenous and foreign sources. The mean water table is much lower at the gully edge, and there are pronounced interannual fluctuations. These conditions have not affected the integrity of the Pb and Cu records but have caused postdepositional mobilization and redistribution of As and Sb. Cumulative inventories show significant loss of As and Sb at the gully edge site. Long-term water table draw-down in ombrotrophic peat bogs has the potential to alter the geochemistry and fate of previously deposited As and Sb.