ZnO:Al thin films deposited by RF-magnetron sputtering with tunable and uniform properties.

Nanostructured, high quality and large area Al-doped ZnO (ZnO:Al) thin films were obtained by radiofrequency (RF) magnetron sputtering. The sample rotation during deposition has resulted in excellent spatial distribution of thickness and electro-optical properties compared to that obtained under static conditions. ZnO:Al thin films are employed in a large number of devices, including thin film solar cells, where the uniformity of the properties is a key factor for a possible up-scaling of the research results to industrially relevant substrate sizes. A chemical post etching treatment was employed achieving tunable surface nanotextures to generate light scattering at the desired wavelength for improved cell efficiency. Since the film resistivity is only slightly increased by the etching, this post-deposition step allows separating the optimization of electro-optical properties from light scattering behavior. The thin films were characterized by FE-SEM, XRD, UV-VIS spectroscopy, four probe and van der Paw techniques.

Examination of the spatial and temporal distribution of sensory cortical activity using a 100-electrode array.

This paper introduces improved techniques for multichannel extracellular electrophysiological recordings of neurons distributed across a single layer of topographically mapped cortex. We describe the electrode array, the surgical implant techniques, and the procedures for data collection and analysis. Neural events are acquired through an array of 25 or 100 microelectrodes with a 400-microm inter-electrode spacing. One advantage of the new methodology is that implantation is achieved through transdural penetration, thereby reducing the disruption of the cortical tissue. The overall cortical territory sampled by the 25-electrode array is 1.6 x 1.6 mm (2.56 mm2) and by the 100-electrode array 3.6 x 3.6 mm (12.96 mm2). Using a recording system with 100 channels available, neural activity is simultaneously acquired on all electrodes, amplified, digitized, and stored on computer. In our data, average peak-to-peak signal/noise ratio was 11.5 and off-line waveform analysis typically allowed the separation of at least one well-discriminated single-unit per channel. The reported technique permits analysis of cortical function with high temporal and spatial resolution. We use the technique to create an 'image' of neural activity distributed across the whisker representation of rat somatosensory (barrel) cortex.

Production and characterization of monoclonal antibodies to human ciliary neurotrophic factor with defined epitope recognition.

Ten mouse hybridoma lines producing monoclonal antibodies (Mabs) against recombinant human ciliary neurotrophic factor (rhCNTF) have been obtained. Two monoclonal antibodies belonging to the IgG1 class were selected and characterized. Their specificity was established by ELISA and Western blotting. Epitopes recognized by the two Mabs were investigated with ELISA and Western blotting by using rhCNTF mutants, rhCNTF fragments and synthetic peptides mimicking different portions of the CNTF molecule. The carboxy-terminal part of the CNTF and particularly the sequence between aa 150 and 159 appeared to constitute the immunodominant group. The fact that certain amino acid sequences of CNTF are conserved among species was utilized to examine the crossreactivity patterns of the two Mabs with rat sciatic nerve CNTF by Western blotting and immunohistochemistry. These antibodies will be useful for studying the distribution of CNTF in the nervous system and in developing an enzyme-linked immunosorbent assay for the quantitative determinations of CNTF in various neuropathologies.

Backbone of complex networks of corporations: the flow of control.

We present a methodology to extract the backbone of complex networks based on the weight and direction of links, as well as on nontopological properties of nodes. We show how the methodology can be applied in general to networks in which mass or energy is flowing along the links. In particular, the procedure enables us to address important questions in economics, namely, how control and wealth are structured and concentrated across national markets. We report on the first cross-country investigation of ownership networks, focusing on the stock markets of 48 countries around the world. On the one hand, our analysis confirms results expected on the basis of the literature on corporate control, namely, that in Anglo-Saxon countries control tends to be dispersed among numerous shareholders. On the other hand, it also reveals that in the same countries, control is found to be highly concentrated at the global level, namely, lying in the hands of very few important shareholders. Interestingly, the exact opposite is observed for European countries. These results have previously not been reported as they are not observable without the kind of network analysis developed here.

Statistical independence and neural computation in the leech ganglion.

In this report, the input/output relations in an isolated ganglion of the leech Hirudo medicinalis were studied by simultaneously using six or eight suction pipettes and two intracellular electrodes. Sensory input was mimicked by eliciting action potentials in mechanosensory neurons with intracellular electrodes. The integrated neural output was measured by recording extracellular voltage signals with pipettes sucking the roots and the connectives. A single evoked action potential activated electrical activity in at least a dozen different neurons, some of which were identified. This electrical activity was characterized by a high degree of temporal and spatial variability. The action potentials of coactivated neurons, i.e. activated by the same mechanosensory neuron, did not show any significant pairwise correlation. Indeed, the analysis of evoked action potentials indicates clear statistical independence among coactivated neurons, presumably originating from the independence of synaptic transmission at distinct synapses. This statistical independence may be used to increase reliability when neuronal activity is averaged or pooled. It is suggested that statistical independence among coactivated neurons may be a usual property of distributed processing of neuronal networks and a basic feature of neural computation.

Integration of multiple-whisker inputs in rat somatosensory cortex.

Rats explore their surroundings through rhythmic movement of their mystacial vibrissae. At any given moment, multiple whiskers are simultaneously moved and may contact the surface of an object. The aim of this work is to understand how simultaneous multiple-whisker deflections are processed in the somatosensory cortex. Arrays of 25 electrodes were inserted into the vibrissal representation of barrel cortex of adult rats. Multi-unit responses were recorded during (i) stimulation of single whiskers, and (ii) simultaneous stimulation of two, three or four whiskers of a whisker arc or whisker row. The whole-array response elicited by the simultaneous stimulation of multiple-whiskers (observed response) was compared to a multiple-whisker response predictor, defined as the sum of the whole-array responses to the separate stimulation of the corresponding single whiskers. The observed response to stimulation of four whiskers was nearly always less than the predicted response, indicating a sublinear summation of multiple coincident inputs. Examining the poststimulus time course of sublinearity, we found that the earliest cortical response to whisker deflection - reflecting the thalamocortical volley - was linear, whereas the successive cortical response was highly sublinear. This suggests a cortical origin of the phenomenon.

Nerve growth factor (NGF) in cerebrospinal fluid (CSF) from patients with various neurological disorders.

It has been recently shown that NGF is not only involved in the survival and development of sympathetic and neural crest-derived sensory neurons, but also in some mechanisms of the immune system. For this reason, we studied the content of NGF in CSF samples from patients with diseases in which neuroimmunological mechanisms seem to be involved (multiple sclerosis, amyotrophic lateral sclerosis, Alzheimer disease, chronic relapsing polyradiculoneuritis, Guillain-Barré syndrome, and tumors of the nervous system), as well as from a number of normal control subjects. We setup an ELISA aimed at the beta subunit of NGF, obtaining good validation tests and a detection limit of 28 pg beta NGF per ml. None of the samples was found to contain detectable levels of NGF and, when a concentration method for sample enrichment was used, only one patient was NGF-positive. This suggests that NGF is probably not involved in the neuroimmunological mechanisms underlying some inflammatory and degenerative diseases of the nervous system.