New England Medical Center Posterior Circulation Stroke Registry II. Vascular Lesions

Among 407 New England Medical Center Posterior Circulation Registry (NEMC-PCR) patients, the extracranial (ECVA) and intracranial vertebral arteries (ICVA) were the commonest sites of severe occlusive disease followed by the basilar artery (BA). Severe occlusive lesions were found in >1 large artery in 148 patients; 134 had unilateral or bilateral severe disease at one arterial location. Single arterial site occlusive disease occurred most often in the ECVA (52 patients, 15 bilateral) followed by the ICVA (40 patients, 12 bilateral) and the BA (46 patients). Involvement of the ICVAs and the BA was very common and some patients also had ECVA lesions. Hypertension, smoking, and coronary and peripheral vascular disease were most prevalent in patients with extracranial disease while diabetes and hyperlipidemia were more common when occlusive lesions were only intracranial. Intra-arterial embolism was the most common mechanism of brain infarction in patients with ECVA and ICVA occlusive disease. ICVA occlusive lesions infrequently caused infarction limited to the proximal territory (medulla and posterior inferior cerebellum). BA lesions most often caused infarcts limited to the middle posterior circulation territory (pons and anterior inferior cerebellum). Posterior cerebral artery occlusive lesions were predominantly embolic. Penetrating artery disease caused mostly pontine and thalamic infarcts. Prognosis was poorest in patients with BA disease. The best prognosis surprisingly was in patients who had multiple arterial occlusive lesions; they often had position-sensitive transient ischemic attacks during months or years

New England Medical Center Posterior Circulation Stroke Registry: I. Methods, Data Base, Distribution of Brain Lesions, Stroke Mechanisms, and Outcomes

Among 407 New England Medical Center Posterior Circulation Registry (NEMC-PCR) patients, 59% had strokes without transient ischemic attacks (TIAs), 24% had TIAs before strokes, and 16% had only posterior circulation TIAs. Embolism was the commonest stroke mechanism accounting for 40% of cases (24% cardiac origin, 14% arterial origin, 2% had potential cardiac and arterial sources). In 32%, large artery occlusive lesions caused hemodynamic brain infarction. Stroke mechanisms in the posterior and anterior circulation are very similar. Infarcts most often included the distal posterior circulation territory (rostral brainstem, superior cerebellum and occipital and temporal lobes), while the proximal (medulla and posterior inferior cerebellum) and middle (pons and anterior inferior cerebellum) territories were equally involved. Infarcts that included the distal territory were twice as common as those that included the proximal or middle territories. Most distal territory infarcts were attributable to embolism. Thirty day mortality was low (3.6%). Embolic stroke mechanism, distal territory location, and basilar artery occlusive disease conveyed the worst prognosis

Carbon monoxide oxidation on nanostructured CuOx/CeO2 composite particles characterized by HREM, XPS, XAS, and high-energy diffraction

Nonstoichiometric CuO x /CeO 2 nanocomposite particles have been synthesized by inert gas condensation (IGC) over the whole compositional range (2 to 98 at.% Cu). The composition influences greatly the formation of various nanostructures, such as core-shells. A wide range of techniques were used to characterize the catalysts: high-resolution TEM and X-ray photoelectron spectroscopy, as well as high-energy diffraction (HED) and X-ray absorption spectroscopy (XANES and EXAFS) using synchrotron radiation. Catalytic oxidation of carbon monoxide was performed on catalysts with equal specific surface area, using both a batch reactor and a fixed-bed flow reactor. X-ray absorption spectroscopy showed that copper was present as a mixture of Cu(I) and Cu(II) species ranging from ca. 36% Cu(I) in one of the fresh samples to less than 5% in the activated samples. The coordination of Cu(I) was found to be mostly linear 2-coordinate as in the model compound Cu 2 O or alternatively 3-coordinate planar, while Cu(II) was found to present a mixture of tetrahedral and highly distorted octahedral coordination. EXAFS showed that both copper species were part of a very dispersed and highly disordered structure. The main chemical factors that control the activity for the oxidation of carbon monoxide are (i) the nanostructured morphology, (ii) the X-ray crystallinity as determined by HED, and (iii) the dispersion of copper at the surface. These three factors can be tailored during the IGC synthesis, but they can also change during the thermal activation. Copper ions migrate toward the particle surface and create new and highly dispersed superficial copper species/clusters, accompanied by a slight reduction of the CeO 2 surface. This favorable morphological evolution, or diminutive structural rearrangement, which was not adequately resolved by HREM, can be monitored as a shift of the light-off temperature. The wide variation in X-ray crystallinity between the catalysts can be used to quantify the processes occurring during the thermal activation. Easily reducible, high-energy surfaces of CeO 2 are better in stabilizing extremely dispersed copper species by a close synergistic interaction, which promotes a rapid change of valency and supply of oxygen. © 2002 Elsevier Science (USA).status: publishe

Morphology and structure of CuOx/CeO2 nanocomposite catalysts produced by inert gas condensation: An HREM, EFTEM, XPS, and high-energy diffraction study

Inert gas condensation (IGC) has been employed to produce nanoparticles of the low-temperature combustion catalyst CuOxCeO2. For the first time we have used a multiple heating crucible setup to tailor various morphologies over the whole compositional range (2-98% Cu). The factors that control the growth, structure, and morphology of the nanocomposite have been studied. A powerful combination of complementary characterization methods has been used to elucidate the catalytic synergistics of this material. Investigations by high-resolution transmission electron microscopy (HRTEM) and energy-filtered TEM (EFTEM) are supported by x-ray photoelectron spectroscopy (XPS) and high-energy diffraction (HED) measurements. The nonstoichiometric CuOx/CeO2 composite displays an amorphous character consisting of aggregated CeO2 (ceria) nanocrystallites over which amorphous copper clusters (or a thin film of a solid solution) are finely dispersed. In the range 6∼20% Cu, copper is predominantly located at the surface, which can give the material optimum catalytic properties. Development of crust structures, for example, core-shells, are formed in the 30∼70% Cu concentration range and is attributable to a sequential oxidation of Ce followed by Cu and an ideal proportion of lattice expansion for the oxides. We suggest a model that illustrates the formation of the crust structure and may explain the observed extreme dispersion of copper on ceria. The helium gas pressure during the thermalization controls the crystal size and the degree of crystallite aggregation. Rounded particle shapes consisting of epitaxially interfaced nanocrystallites exhibit an x-ray amorphous character, while block-shaped crystals displaying sharp edges and distinct flat surfaces give rise to a higher x-ray crystallinity. Bulk CuO crystals were detected by high-energy diffraction above a 30% Cu content. However, the extreme copper dispersion is preserved even for higher copper contents, showing no limit of surface saturation.status: publishe

Growth of Straight InAs-on-GaAs Nanowire Heterostructures

One of the main motivations for the great interest in semiconductor nanowires is the possibility of easily growing advanced heterostructures that might be difficult or even impossible to achieve in thin films. For III␣V semiconductor nanowires, axial heterostructures with an interchange of the group III element typically grow straight in only one interface direction. In the case of InAs␣GaAs heterostructures, straight nanowire growth has been demonstrated for growth of GaAs on top of InAs, but so far never in the other direction. In this article, we demonstrate the growth of straight axial heterostructures of InAs on top of GaAs. The heterostructure interface is sharp and we observe a dependence on growth parameters closely related to crystal structure as well as a diameter dependence on straight nanowire growth. The results are discussed by means of accurate first principles calculations of the inter- facial energies. In addition, the role of the gold seed particle, the effect of its composition at different stages during growth, and its size are discussed in relation to the results observed

Auditory Prosthesis with a Penetrating Nerve Array

Contemporary auditory prostheses (“cochlear implants”) employ arrays of stimulating electrodes implanted in the scala tympani of the cochlea. Such arrays have been implanted in some 100,000 profoundly or severely deaf people worldwide and arguably are the most successful of present-day neural prostheses. Nevertheless, most implant users show poor understanding of speech in noisy backgrounds, poor pitch recognition, and poor spatial hearing, even when using bilateral implants. Many of these limitations can be attributed to the remote location of stimulating electrodes relative to excitable cochlear neural elements. That is, a scala tympani electrode array lies within a bony compartment filled with electrically conductive fluid. Moreover, scala tympani arrays typically do not extend to the apical turn of the cochlea in which low frequencies are represented. In the present study, we have tested in an animal model an alternative to the conventional cochlear implant: a multielectrode array implanted directly into the auditory nerve. We monitored the specificity of stimulation of the auditory pathway by recording extracellular unit activity at 32 sites along the tonotopic axis of the inferior colliculus. The results demonstrate the activation of specific auditory nerve populations throughout essentially the entire frequency range that is represented by characteristic frequencies in the inferior colliculus. Compared to conventional scala tympani stimulation, thresholds for neural excitation are as much as 50-fold lower and interference between electrodes stimulated simultaneously is markedly reduced. The results suggest that if an intraneural stimulating array were incorporated into an auditory prosthesis system for humans, it could offer substantial improvement in hearing replacement compared to contemporary cochlear implants