Preparation and HREM characterization of a protonated form of a layered perovskite tantalate from an Aurivillius phase Bi(2)SrTa(2)O(9) via acid treatment.

An Aurivillius phase, Bi(2)SrTa(2)O(9), which consists of perovskite-like slabs and bismuth oxide sheets, was treated with 3 M hydrochloric acid for 72 h, and the resultant product was characterized. Scanning electron microscopy investigation indicated that no morphological change occurred during the acid treatment. X-ray diffraction (XRD) analysis revealed that the product exhibited tetragonal symmetry with a = 0.391 +/- 0.004 nm and c = 0.98 +/- 0.01 nm, and the a parameter is consistent with a typical value for cubic perovskite oxides. High-resolution electron microscopy (HREM) observations along both [001] and [010] showed that the structure of the perovskite-like slabs in Bi(2)SrTa(2)O(9) was retained after the acid treatment. The compositional analyses revealed the loss of a large portion of bismuth and a part of strontium (present in the bismuth oxide sheets due to B <--> Sr disorder) and the introduction of protons. These observations indicate that the bismuth oxide sheets in Bi(2)SrTa(2)O(9) were selectively leached and that protons were introduced into the interlayer space to form a protonated layered perovskite, H(1.8)[Sr(0.8)Bi(0.2)Ta(2)O(7)]. Though diffraction techniques (XRD and electron diffraction) demonstrated that an average structure of H(1.8)[Sr(0.8)Bi(0.2)Ta(2)O(7)] consisted of perovskite-like slabs stacked without displacement, HREM observation along [010] demonstrated that both a simple stacking sequence without displacement (P-type) and a stacking sequence with a relative displacement by (a + b)/2 (I-type) were present in H(1.8)[Sr(0.8)Bi(0.2)Ta(2)O(7)].

Cross-sectional shapes of the internal auditory canal in patients with acoustic neuromas.

Cross-sectional images of the internal auditory canal (IAC) were investigated in 23 patients with acoustic neuroma in order to clarify the widening of the IAC. The area of the IAC and the ratio of areas (neuroma side:normal side) were calculated. The shape of the IAC was fitted by an ellipse to obtain the length of the axes and the direction of the long axis. The area of the IAC was 34.2+/-12.2 mm2 in the neuroma side and 18.1+/-4.8 mm2 in the normal side. The neuroma side was larger than the normal side in all patients, and the mean ratio of areas was 1.9. However, the degrees of cochlear and vestibular damage did not correlate with the ratio of areas. The mean ratio of axes of the approximated ellipse was 1.17+/-0.09 in the neuroma side and 1.14+/-0.10 in the normal side; however, no significant difference was seen between the ratio of axes. The directions of the long axes were not always consistent with the positions of the originating nerves of the tumour. Referring to hypothetical models of enlargement of the IAC, our data suggest that the widening of the IAC in the acoustic neuroma was expansive. The data also indicated that symptoms of the acoustic neuroma were caused not only by compression of the nerves but also by other mechanisms, such as vascular insufficiency to the inner ear.

Ordered nanoporous arrays of carbon supporting high dispersions of platinum nanoparticles.

Nanostructured carbon materials are potentially of great technological interest for the development of electronic, catalytic and hydrogen-storage systems. Here we describe a general strategy for the synthesis of highly ordered, rigid arrays of nanoporous carbon having uniform but tunable diameters (typically 6 nanometres inside and 9 nanometres outside). These structures are formed by using ordered mesoporous silicas as templates, the removal of which leaves a partially ordered graphitic framework. The resulting material supports a high dispersion of platinum nanoparticles, exceeding that of other common microporous carbon materials (such as carbon black, charcoal and activated carbon fibres). The platinum cluster diameter can be controlled to below 3 nanometres, and the high dispersion of these metal clusters gives rise to promising electrocatalytic activity for oxygen reduction, which could prove to be practically relevant for fuel-cell technologies. These nanomaterials can also be prepared in the form of free-standing films by using ordered silica films as the templates.

Structural elucidation of microporous and mesoporous catalysts and molecular sieves by high-resolution electron microscopy.

Twenty years ago, one of us embarked (Bursill, L. A.; Lodge, E. A.; Thomas, J. M. Zeolitic structures as revealed by high-resolution electron microscopy. Nature 1980, 286, 111-113) on the study of zeolites (renowned for their electron-beam sensitivity) by high-resolution transmission electron microscopy (HRTEM). In the ensuing years, high-resolution imaging aided by optical diffractometry has yielded details of the open framework structures of a number of new aluminosilicate and aluminophosphate molecular sieves and catalysts. The nature of intergrowth and recurrently twinned structures, as well as new types of structural imperfection in hitherto uncharacterized materials, has also been elucidated. With continued improvements in instrumental development, encompassing higher accelerating voltages, better objective lenses and vacua, computational advances, and the arrival of slow-scan CCD detectors, electron crystallographic methods and HRTEM imaging now enable the ab initio three-dimensional structures of micro- and mesoporous solids, with their occluded structure-directing organic species, to be determined. High-resolution scanning transmission electron microscopy using subnanometric probes provides supplementary structural and ultramicro analytical information and electron spectroscopic imaging (at the attogram level). In its high-angle annular dark-field mode, it is capable of locating and determining the composition of individual nanoparticle catalysts (consisting of just a few atoms) supported on porous hosts.

An HREM study of channel structures in mesoporous silica SBA-15 and platinum wires produced in the channels.

The hyperbolic geometry of the pores in SBA-15 are drawn into a three-dimensional structure by small lateral pores, distributed in a random way, as shown in the picture, which interconnect the main channels. This construction was established by forming a "negative" of the structure with platinum precipitated in the channel and dissolving the SBA-15 material.

Direct imaging of the pores and cages of three-dimensional mesoporous materials.

Mesostructured composite materials, with features ranging from 20 to 500 A in size, are obtained by the kinetically controlled competitive assembly of organic and inorganic species into nanostructured domains. Short-range order is limited, and long-range order is determined by weak forces such as van der Waals or hydrogen-bonding. Three-dimensional mesoporous materials obtained by removing the organic phase are of particular interest for applications such as catalysis and chemical sensing or separation, for which structural features such as cavity shape, connectivity and ordered bimodal porosity are critical. But atomic-scale structural characterization by the usual diffraction techniques is challenging for these partially ordered materials because of the difficulty in obtaining large (> 10 microm) single crystals, and because large repeat spacings cause diffraction intensities to fall off rapidly with scattering angle so that only limited small-angle data are available. Here we present a general approach for the direct determination of three-dimensional mesoporous structures by electron microscopy. The structure solutions are obtained uniquely without pre-assumed models or parametrization. We report high-resolution details of cage and pore structures of periodically ordered mesoporous materials, which reveal a highly ordered dual micro- and mesoscale pore structure.

Dipole estimation of alpha EEG during alcohol ingestion in males genotypes for ALDH2.

Using a dipole tracing method based on the two-dipole model, the purpose of the present study was to investigate alcohol-induced changes in the alpha band of electroencephalogram (EEG) and its equivalent current dipoles (ECDs) in 12 healthy male volunteers, who were genetically typed for mitochondrial aldehyde dehydrogenase-2 (ALDH2). The alpha power and the mean interval dipolarity, which represents the goodness of fit of alpha EEG with the two-dipole model, increased at 30 min after 0.75 ml/kg of alcohol ingestion, when breath alcohol concentration showed its peak. However, the location of ECDs and distribution of alpha EEG did not change after alcohol ingestion. These findings indicate that alcohol enhances alpha EEG but does not change the location of its electrical sources. Interestingly, the time course of alcohol-induced EEG changes differed significantly according to the aversive flushing reaction after its intake. From 60 to 120 min, the non-flushing group which had homozygous ALDH2* 1 (active type) displayed significant increase not only in the alpha power but also in the interval dipolarity compared to the baseline, whereas the flushing group with heterozygous ALDH2*1/2*2 (inactive type) did not exhibit this significant increase. The difference in the time course was discussed from the viewpoint of the protective effect of ALDH2*2 allele against the risk for alcoholism. These results suggest that the dipole tracing method could provide an alternative neurophysiological marker for the risk for alcoholism.

Serotonin 5-HT2 receptors in schizophrenic patients studied by positron emission tomography.

Using positron emission tomography (PET) and [11C]N-methylspiperone (NMSP), we examined 5-HT2 receptors in the cortex of schizophrenic patients in whom we previously observed decreased prefrontal D1 receptor binding. The subjects were 10 neuroleptic-naive schizophrenic patients, 7 schizophrenic patients who were drug-free but had previously been treated with neuroleptics, and 12 normal controls. A non-significant trend towards decreased prefrontal [11C]NMSP binding was observed in the neuroleptic-treated patients, suggesting a possible effect of previous neuroleptic treatment on the alteration in cortical 5-HT2 function. However, the neuroleptic-naive patients showed no noticeable difference in cortical [11C]NMSP binding compared to controls. Our results do not rule out the role of 5-HT2 function as a crucial site of therapeutic activity of schizophrenia, but they do suggest that cortical 5-HT2 receptors might not be primarily involved in the pathophysiology of schizophrenia.

Dynamic mediolateral activation of the pyramidal cell population in human somatosensory 3b area can be visualized by magnetic recordings.

Dynamic mediolateral activation in the pyramidal cell population of the human somatosensory 3b area was studied non-invasively. Somatosensory evoked fields (SEFs) were recorded over the hand area contralateral to the right median nerve stimulation at the wrist. Localization of an equivalent current dipole (ECD) for N20m primary cortical response was successively calculated for periods of 2.4 ms around N20m peak where the signal-to-noise ratio exceeded 100 and the spatial resolution was approximately 0.3 mm. The ECD moved toward the anterior, lateral and inferior direction for a distance of 8.7 mm at a propagation velocity of 3.6 m/s. This direction was orthogonal to the orientation of apical dendrites of the pyramidal neurons in area 3b and parallel to the surface of the posterior bank of the central sulcus. These findings suggest that the sequential mediolateral activation of the pyramidal cells in the somatosensory cortex is mediated by horizontal connections running parallel to the cortical surface.

Distal-proximal somatotopy in the human hand somatosensory cortex: a reappraisal.

The distal-proximal representation of the finger and palm in the first somatosensory cortex was reexamined. Somatosensory evoked magnetic fields (SEFs) were measured with a 37-channel first-order axial gradiometer system. Sensory stimulus comprising a 20-ms vibration at a frequency of 200 Hz was delivered to five successive sites in 3-cm increments along the distal-proximal direction over the volar surface of the right index finger and palm. Using a single dipole model, the sources and the signal strengths of the main peak (M50) of the SEFs were estimated. All of the sources were located in the 3b area. There were no statistically significant differences between the locations of dipoles evoked by stimulation of different sites. The results support those of our previous study using a 122-channel whole-head planar gradiometer system that orderly distal-proximal representation of the hand, as described in monkeys, is blurred in the adult human somatosensory cortex.

Reciprocal modulation of somatosensory evoked N20m primary response and high-frequency oscillations by interference stimulation.

OBJECTIVES: We examined whether the inverse relation between somatic evoked N20m primary response and high-frequency oscillations during a wake-sleep cycle (Hashimoto, I., Mashiko, T., Imada, T., Somatic evoked high-frequency magnetic oscillations reflect activity of inhibitory interneurons in the human somatosensory cortex, Electroenceph clin Neurophysiol 1996;100:189-203) holds for interference stimulation. METHODS: Somatosensory evoked fields (SEFs) from 14 subjects were measured following electric median nerve stimulation at the wrist with, and without, concurrent brushing of the palm and fingers. SEFs were recorded with a wide bandpass (0.1-1200 Hz) and then N20m and high-frequency oscillations were separated by subsequent low-pass (< 300 Hz) and high-pass (> 300 Hz) filtering. RESULTS: The N20m decreased dramatically in amplitude during interference stimulation. In contrast, the high-frequency oscillations moderately increased in number of peaks. CONCLUSIONS: These results demonstrate the presence of an inverse relation between N20m and high-frequency oscillations for interference stimulation. We speculate that the high-frequency oscillations represent a localized activity of GABAergic inhibitory interneurons of layer 4, characterized by a high-frequency spike burst (200-1000 Hz) without adaptation, and that the continuous interference stimulation induces tonic excitation of the interneurons, leading to a facilitation of responses to the coherent afferent volley elicited by the median nerve stimulation (bottom-up mechanism). On the other hand, refractoriness of the pyramidal neurons caused directly by interference stimulation along with an enhanced feed-forward inhibition from the interneurons will lead to a decrease of N20m amplitude.

Frequency representation in the human hand somatosensory cortex: a reappraisal.

Frequency organization in the human primary somatosensory cortex (SI) was re-examined. Somatosensory evoked magnetic fields (SEFs) were measured with a 37 channel first-order axial gradiometer system. Sensory stimuli comprising a 20ms vibration at frequencies of 50, 100, 200 and 400 Hz were delivered to the volar surface of the tip of the right index finger. Using a single dipole model, the sources of the first main peak (M50) of SEFs were estimated. All of the sources were located in the 3b area. There were no statistically significant differences between the locations of the dipoles evoked by different frequency stimulations. These results support our previous study using a 122 channel whole head planar gradiometer system that systematic frequency organization at the hand area of SI cortex may not be present in humans.

Decreased prefrontal dopamine D1 receptors in schizophrenia revealed by PET.

Schizophrenia is believed to involve altered activation of dopamine receptors, and support for this hypothesis comes from the antipsychotic effect of antagonists of the dopamine D2 receptor (D2R). D2R is expressed most highly in the striatum, but most of the recent positron emission tomography (PET) studies have failed to show any change in D2R densities in the striatum of schizophrenics, raising the possibility that other receptors may also be involved. In particular, the dopamine D1 receptor (D1R), which is highly expressed in the prefrontal cortex, has been implicated in the control of working memory, and working memory dysfunction is a prominent feature of schizophrenia. We have therefore used PET to examine the distribution of D1R and D2R in brains of drug-naive or drug-free schizophrenic patients. Although no differences were observed in the striatum relative to control subjects, binding of radioligand to D1R was reduced in the prefrontal cortex of schizophrenics. This reduction was related to the severity of the negative symptoms (for instance, emotional withdrawal) and to poor performance in the Wisconsin Card Sorting Test. We propose that dysfunction of D1R signalling in the prefrontal cortex may contribute to the negative symptoms and cognitive deficits seen in schizophrenia.

Three-dimensional computed imaging using a personal computer for nasal surgery.

Three-dimensional (3-D) computed imaging was applied before surgery in 16 patients with nasal or paranasal disease. The images obtained by computed tomography (CT) were scanned by a personal computer. The contours of the organs were outlined on the scanned images, and the images were then reconstructed using 3-D imaging software. The resulting 3-D images were evaluated and compared with actual surgical images. The 3-D images were found to be useful for surgical procedures, because they facilitated recognition of the topologic relation between structure and lesion. Although this method requires a personal computer and an image scanner, it is cheaper than, and in some respects even superior to, a 3-D CT system.