1,721,015 research outputs found
A pair of clamps for a safe removing and repositioning of beta and gamma angular settings of Brown-Roberts-Wells stereotactic system during operation
No full textThe Brown-Roberts-Wells are system is a non-target-centered design, i.e., without an independent approach angle. The approach angle of this system strictly depends on precalculated values (entry and target point). Therefore, some components of the system used sometimes prevent a direct insight into the operation field. Once the entry point has been set, the are system normally has to be taken off to permit an unimpeded approach to the burr here. To facilitate rotation and return to the primary beta and gamma angular settings during stereotactic craniotomy and other surgery, a pair of clamps was designed for the BRW are system. These clamps help the approach to the entry point in such a way that some components of the are (e.g., the guide block holder) are removed from the surgical field, thus giving wide visual access for the stereotactic approach. Consequently, it is no longer necessary to remove the entire are system, resulting in an increased operation safety and shorter operation times
Peroperative cardiovascular stability during brainstem surgery. The use of high-dose methylprednisolone compared to dexamethasone - A retrospective analysis
No full textBackground: In neurosurgical procedures within brainstem structures, corticosteroids are routinely administered to prevent oedema and to reduce intraoperative trauma, After replacing the routine administration of dexamethasone (DX) by high-dose methylprednisolone (MP) during surgery for tumours within brainstem structures, a decreased incidence of intraoperative haemodynamic instability events was observed. To test this hypothesis, a retrospective analysis was performed. Methods: Peroperative data of 62 surgical procedures of brainstem tumours were retrospectively analysed with respect to haemodynamic instability requiring changes in surgical strategy and/or emergence medication with vasoactive drugs. Severe changes in haemodynamic parameters were defined as a significant increase or decrease in heart rate and/or mean arterial blood pressure greater than 30% compared to baseline values. From 1988 to 1994, intravenous dexamethasone was given peroperatively in 33 patients. After a bolus of 1 mg kg(-1) body weight (BW) 30 min preoperatively, 0.2 mg kg(-1) were given every 4 h. From 1994 until now, methylprednisolone was administered instead of dexamethasone in 29 patients. After an initial bolus of 30 mg kg(-1) BW immediately before surgery, 5.4 mg kg(-1) h(-1) were given 23 h postoperatively. Results: The results of this retrospective analysis suggest that the number of operations with episodes of bradycardia, arterial hypotension (P<0.05), tachycardia and arterial hypertension (P<0.005) was significantly decreased in the group of patients treated with high-dose methylprednisolone. Conclusion: The retrospective analysis of the clinical data showed that the routine use of high-dose methylprednisolone was associated with a decreased incidence of haemodynamic instability in a selected group of patients undergoing brainstem surgery. This finding has to be proven in prospective double-blind controlled studies. (C) Acta Anaesthesiologica Scandinavica 44 (2000)
Intrinsic brainstem tumours in adults: results of microneurosurgical treatment of 16 consecutive patients
No full textIntrinsic brainstem tumours in adults have a poor prognosis and surgical resection is rarely performed. Encouraged by successful operations on children performed in our department, we began a more aggressive strategy of open operations. Between 1986 and 1997, we operated upon 16 consecutive patients over 16 years of age (five female, 11 male, mean age 36.9 years) who were suffering from intrinsic tumours located in the pons and/or medulla oblongata. The extent of first open resection was 80 - 100% in two of the cases and more than 50% in nine cases. The mean survival time after the first occurrence of symptoms was 88.1 ( median 34.5) months, and 39.9 ( median 11) months after the first open operation. The rate of 5-year survival from the first occurrence of symptoms was 37.5% (25% after the first open surgical procedure). Thirteen out of 16 patients died within the follow-up period of at least 6.3 years, two of them within the immediate postoperative period. Eleven patients experienced a postoperative deterioration of symptoms from which only four recovered. Eight patients had from WHO grade II astrocytoma and a similar course as patients with higher-grade gliomas (n=4). Our results indicate that open microneurosurgery for intrinsic brainstem tumours is of questionable benefit for the patient. Although surgery offers the advantages of reliable confirmation of histopathology and may be associated with prolonged survival, neurological deterioration was common and, unlike in paediatric patients, often irreversible
Multiple Birds with One Stone: Beating 1/2 for EFX and GMMS via Envy Cycle Elimination
No full textSeveral relaxations of envy-freeness, tailored to fair division in settings with indivisible goods, have been introduced within the last decade. Due to the lack of general existence results for most of these concepts, great attention has been paid to establishing approximation guarantees. In this work, we propose a simple algorithm that is universally fair in the sense that it returns allocations that have good approximation guarantees with respect to four such fairness notions at once. In particular, this is the first algorithm achieving a (φ−1)-approximation of envy-freeness up to any good (EFX) and a 2/φ+2 -approximation of groupwise maximin share fairness (GMMS), where φ is the golden ratio. The best known approximation factor, in polynomial time, for either one of these fairness notions prior to this work was 1/2. Moreover, the returned allocation achieves envy-freeness up to one good (EF1) and a 2/3-approximation of pairwise maximin share fairness (PMMS). While EFX is our primary focus, we also exhibit how to fine-tune our algorithm and improve further the guarantees for GMMS or PMMS.Finally, we show that GMMS—and thus PMMS and EFX—allocations always exist when the number of goods does not exceed the number of agents by more than two
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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