1,721,023 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The pain in optic neuritis: A manifestation of visceralis hyperalgesia [Il dolore nelle neuriti ottiche: una manifestazione di iperalgesia viscerale]
No full textIn both retrobulbar and intrabulbar neuropathies a painful symptomatology may occur before or simultaneously to the diminution of visual acuity. The anatomical relationship between extraocular muscles and the optic nerve sheath at the orbital apex could help explain the mechanism involved in the manifestations of pain. We studied 52 patients suffering from optic neuritis. A painful symptomatology of varying types, was present in one patient out of the 5 cases with intrabulbar optic neuritis and in 28 out of the 47 patients with retrobulbar optic neuritis (59.57%). Because of the way in which it is manifested and the type of receptors that are stimulated pain in optic neuritis is considered visceral cluster and migraine headaches are among the best known visceral pains. According to Sicuteri, in these patients, the system of modulation - inhibition of pain is impaired and visceral hyperalgesia occurs. Such a condition may be revealed clinically by means of simple test of ischemia and stasis of the upper limb. We studied 28 cases out of all our patients in order to detect the presence of visceral hyperalgesia. We tested the statistical significance for the association between pain and positivity for Sicuteri test. Results were statistically significant (χ2 test = 5.103, p = 0.024). The significant association between optic neuritis and hyperalgesia suggest that pain in optic neuritis occurs when the nociceptive system is impaired
A linear time-varying approach for robustness analyses of a re-entry flight technology demonstrator
Get PDFA novel robustness analysis technique is proposed for atmospheric re-entry applications. The problem is stated as a finite time stability (FTS) analysis of linear time-varying (LTV) systems on a compact time domain, subject to bounded variations in initial state and unknown parameters. The FTS property is formulated as the inclusion of all the possible system trajectories into a pre-specified time-varying subset of the state space. Based on assuming the involved sets are polytopes, the proposed approach allows deducing the system FTS from the property verification on a limited number of numerically computed system trajectories. An additional result is presented which allows determination of a conservative estimate of the maximum norm-bound of time-varying perturbations under which the LTV system remains finite time stable. Results of the application of the proposed technique to a re-entry technology demonstrator are presented which demonstrate its effectiveness in complementing conventional linear time invariant-based analyses. Results also show that it is computationally viable and allows linking the system robustness to a quantitative analysis of the system trajectory dispersion around the nominal one due to concurrent initial state dispersion and uncertain parameters effects, which aids in evaluating mission objectives fulfillment
A hybrid approach to robustness analyses of flight control laws in re-entry applications
Get PDFThe present paper aims at improving the efficiency of the robustness analyses of flight control laws with respect to conventional techniques, especially when applied to vehicles following time-varying reference trajectories, such as in an atmospheric re-entry. A nonlinear robustness criterion is proposed, stemming from the practical stability framework, which allows dealing effectively with such cases. A novel approach is presented, which exploits the convexity of linear time varying systems, coupled to an approximate description of the original nonlinear system by a certain number of its time-varying linearizations. The suitability of the approximating systems is evaluated in a probabilistic fashion making use of the unscented transformation technique. The effectiveness and potentials of the method are ascertained by application to the robustness analysis of the longitudinal flight control laws of the Italian Aerospace Research Center (CIRA) experimental vehicle USV
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