161,594 research outputs found
On the complexity of the robust stability problem for linear parameter varying systems
No full textIn this paper, it is shown that the problem of checking robust stability of linear parameter varying (LPV) systems is -hard, and therefore, it is rather unlikely to find polynomial-time solution procedures for this problem. In the frequency-domain structured uncertainty case, it is known that the robust stability problem is -hard (Toker and Özbay, 1995; Toker, 1995; Poljak and Rohn, 1993; Nemirovski, 1993; Braatz et al., 1994), but allowing the uncertain blocks to be time varying gives a computationally tractable problem (Shamma, 1994; Poolla and Tikku, 1995), which can be solved by convex optimization techniques. In the parameteric uncertainty case, -hardness of the robust stability problem has been shown in (Poljak and Rohn, 1993; Nemirovski, 1993). The results of this paper show that, allowing the uncertain parameters to be time varying, does not give a computationally simpler problem i.e. it remains -hard, and hence it is rather unlikely to find computationally tractable solution procedures for this problem. On the other hand, as far as the existence of an algorithm is considered, there is still no known (non-polynomial time) algorithm for the robust stability problem of linear parameter varying systems (Lagarias and Wang, 1995), and the well-known Tarski's theorem (Tarski, 1951) does not provide a solution procedure (Kozyakin, 1990). Recently, there has been some developments in the direction of constructing non-polynomial-time algorithms for a related problem, called the joint spectral radius (JSR) computation problem (Lagarias and Wang, 1995). We also comment on the use of these results for developing a non-polynomial-time algorithm for testing robust stability of linear parameter varying systems
Variations on the Author
No full text“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
Influence of serum levels of sex hormones on intraocular pressure in menopausal women
No full textPurpose: The purpose of this study was to assess the effect that changes in sex hormone levels have on intraocular pressure (IOP) in menopausal women. Subjects and Methods: Thirty menopausal women on hormone replacement therapy and 32 menopausal women who had never received hormone replacement therapy (HRT), matched for age and duration of amenorrhea, participated in this study. Intraocular pressures were measured with Goldmann applanation tonometer. Serum levels were measured for estradiol, free testosterone, and follicle stimulating hormone (FSH). The influence of serum hormone levels on IOP was assessed by correlation analysis. Results: The mean IOP of postmenopausal women receiving HRT (13.29 +/- 2.28 mm Hg) was not significantly different from that of menopausal women not receiving HRT (13.56 +/- 2.5 min Hg, P = 0.24). Higher testosterone levels were associated with higher IOPs in women receiving HRT (r = 0.48, P = 0.02) and in those not receiving HRT (r = 0.42, P = 0.003). No significant correlations were observed between IOP and serum levels of estradiol and FSH in either group. Conclusion: Our data provide evidence for a relation between serum testosterone levels and IOP in menopause. Higher testosterone seems to have a tendency to increase IOP in menopausal women
Crystalline silicon diodes as neutron detectors: Performances and perspectives
No full textThe design and development of crystalline silicon neutron detectors are discussed. Experimental results obtained on prototype systems, namely a diode and a microstrip device, are reported. The detector performances are discussed with special emphasis on detection efficiency, dead-time and positional resolution. Performances in signal-to-noise ratio when switching from medium-speed to fast VLSI readout electronics are reported for the prototype systems. Progress through various detection schemes is outlined and the expected performances of a position sensitive area detector for neutron scattering application are presented
Solid state neutron detectors
No full textThe performance of crystalline silicon diodes for operation as cold to thermal neutron detectors are reviewed. Recent advances in both detector technology and VLSI readout electronics open up new possibilities for these devices. Neutron test measurements carried out on two prototype detectors are reported together with the results of a Monte Carlo simulation of detector operation
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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 influence of sex hormones on ocular blood flow in women
No full textPurpose: To investigate the influence of sex hormones on ocular haemodynamics, blood flow velocities in the ophthalmic and central retinal arteries and serum levels of sex hormones were measured in pre- and postmenopausal women. Methods: Colour Doppler imaging (CDI) was used to determine the flow velocities (peak systolic velocity [PSV] and end-diastolic velocity [EDV]) and the resistive index (RI) in the ophthalmic and central retinal arteries in 22 premenopausal and 32 postmenopausal women, who had never received hormone replacement therapy. Serum levels were measured for oestradiol, free testosterone and follicle-stimulating hormone. The CDI parameters were compared between the two groups and the influence of serum levels of oestradiol and testosterone on blood flow velocities and the resistive indices were analysed. Results: After correcting for age and mean arterial blood pressure, an analysis of covariance disclosed a significantly lower EDV (p = 0.02) and a significantly higher RI (p = 0.01) in the central retinal artery of postmenopausal women compared with premenopausal women. Partial correlation analysis, controlling for age, revealed significant correlations between the CDI parameters and serum levels of oestradiol and testosterone. For premenopausal women, PSV (r = 0.58, p = 0.04) and EDV (r = 0.73, p = 0.006) in the ophthalmic artery correlated positively with serum oestradiol levels. The RI in the central retinal artery decreased with increasing oestradiol levels in both groups (premenopausal r = - 0.40, p = 0.04; postmenopausal r = - 0.32, p = 0.05). Peak systolic velocity in the central retinal artery correlated negatively (r = - 0.49, p = 0.04), whereas the RI correlated positively (r = 0.53, p = 0.02) with testosterone levels in the premenopausal group. Postmenopausal women with higher testosterone levels had lower EDV (r = - 0.53, p = 0.007) in the central retinal artery and higher RI in both vessels (ophthalmic artery r = 0.48, p = 0.01; central retinal artery r = 0.61, p = 0.002). Conclusion: Our data provide evidence of a relationship between serum sex hormone levels and blood flow velocities and resistive indices in retrobulbar arteries. Oestradiol appears to have beneficial effects on ocular haemodynamics, whereas testosterone may act as an antagonistic to the effects of oestrogen
Beyşehir Gölü güneyi - Çetmi yöresinin stratgrafisi
No full textABSTRACT Masters Thesis STRATIGRAPHY OF THE SUOTHERN PART O? BEYŞEHİR LAKE-ÇETHİ REGİON Erkan EKMEKÇÎ Ankara University- Graduate School of Natural and Applied Sciences Department of Geological Engineering Supervisor: Prof. Dr. Vedia TOKER 1993, Page: 85 Jury : Prof. Dr. Vedia TOKER Prof. Dr. Nurettin SONEL Prof. Dr. Baysal BATMAN The area investigated is located in the western part of the Central Taurides in which units crop out belonging to the autochthonous and/or paraautochthonous Geyikdağı Group and allochthonous Aladag Group. Geyikdağı Group comprises carbonates and detrital rocks of Late Liassic to Lutetian. These deposits are divided into four structural units according to the stratigraphic position, lithological differences and tectonical lines. These structural units from bottom to top and west to east are Melikdag, Doşdagı, Yelekdagı and Akseki units. Each of them contains different formation in place and these units have been thrust ed on top of eachother. Rock units belonging to the Aladag Group are allochthonous units which tectoniccaly overlie the Akseki unit. These units comprise the Liassic-Late Senonian aged Çamlık formation and ophiolites that have been emplaced after Lutetian in age. Tectonic structures of folding, fracturing and thrusting that observed in the study area are the result of the compressional forces acting along NE-SW direction of Late Tortonian. Thrusting is the most important geological structure formed by this force. The boundries of four different structural units which are distinguished from the Geyikdağı otochthonous has been determined according to these overthusts. KEY WORDS i Geyikdağı Group, Central Taurides, Zilan formation, Lithostratigraphy, Cretaceous, Paleosene, Eocene.ÖZET Yüksek. Lisans Tezi BEYŞEHİR GÖLÜ GÖNBYİ-ÇETMİ YÖRESİNİN STRATİGRAFİSİ Erkan EKMEKÇİ Ankara Üniversitesi Fen Bilimleri Enstitüsü Jeoloji Mühendisliği Anabilim Dalı Danışman: Prof. Dr. Vedia TOKER 1993, Sayfa: 85 Jüri : Prof. Dr. Vedia TOKER Prof. Dr. Nurettin SONEL Prof. Dr. Baysal BATMAN Orta Toroslarm batı bölümünde yer alan inceleme alanında otokton ve/veya paraotokton konumlu Geyikdagı Birliği ile allokton kunumlu Aladağ Birliği 'ne ait birimler yüeylemektedir. Geyikda&ı Birligi'ne ait birimler Geç Liyas-Lütesiyen zaman aralığında çökelmiş karbonat ve kırıntılı kayaçlardan oluşurlar. Bu birimler kendi içerisinde stratigrafi istifleri, litoloji ayrıcalıkları ve tektonik hatlar dikkate alınarak dört yapısal birime ayrılmıştır. Bunlar alttan üste ve batıdan doğuya doğru; Melikdağ Birimi, Döşdagı Birimi, Yelekdagı Birimi, akseki Birimi'dir. Bu yapısal birimlerin herbiri yer yer farklı formasyonlar içerirler ve birbirleri üzerinde bindirmeli yapılar oluştururlar, Aladag Birligi'ne ait olan birimler ise allokton konumlu olup Akseki Birimi üzerinde tektonik olarak yer alırlar. Liyas-Geç Senoniyen yaşlı Çamlık formasyonu ve ofiyolitler ile temsil edilen bu birimler bölgeye Lûtesiyen sonrası yerleşmişlerdir. Çalışma alanında izlenen kıvrımlı, kırıklı ve bindirmeli tektonik yapılar, büyük ölçüde Geç Tortoniyen * de gelişen KD-GB yönlü sıkıştırma kuvvetlerinin etkisi altında oluşmuştur. Buna bağlı olarak gelişen en belirgin yapı stili bindirmelerdir. Geyikdağı otoktonunda ayırt lanan dört ayrı yapısal birimin sınırları bu bindirmelerle belirlenmiştir. ANAHTAR KELİMELERİ Geyikdağı Birliği, Orta Toroslar, Zilan formasyonu, Litostratigrafi, Akseki Birimi, Kretase, Paleosen, Eosen
Larry O. Spencer, Conference Author Presentation
No full textGen. Larry O. Spencer, USAF (Ret.), author of Dark Horse: A Journey from the Horseshoe to the Pentago
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