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Search Results: 1 - 10 of 406678 matches for " Philip M Meyers "
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Revisiting normal perfusion pressure breakthrough in light of hemorrhage-induced vasospasm
Matthew D Alexander, E Sander Connolly , Philip M Meyers
World Journal of Radiology , 2010,
Abstract: Cerebral arteriovenous malformations (AVMs) have abnormally enlarged arteries and veins prone to spontaneous hemorrhage. Immediately following surgical excision of a cerebral AVM, even normal brain tissue surrounding the lesion is subject to hemorrhage, a phenomenon termed normal perfusion pressure breakthrough (NPPB) syndrome. According to this theory, arteries supplying cerebral AVMs become dilated and lose their capacity to dilate or constrict to autoregulate pressure. Acutely after removal of a cerebral AVM, excessive blood pressure in these arterial feeders can cause normal brain tissue to bleed. However, this theory remains controversial. We present a patient with a cerebral AVM that demonstrated cerebrovascular reactivity and argues against an assumption underlying the theory of NPPB syndrome.
Update on the natural history of intracranial atherosclerotic disease: A critical review
Ricardo J Komotar, Christopher P Kellner, Daniel M Raper, Dorothea Strozyk, Randall T Higashida, Philip M Meyers
World Journal of Radiology , 2010,
Abstract: Intracranial atherosclerotic disease (ICAD) contributes to a significant number of ischemic strokes. There is debate in the recent literature concerning the impact of the location of stenosis in ICAD on outcome. Some reports have suggested that disease processes and outcomes vary by vessel location, potentially altering the natural history and indications for intervention. Here we have performed a comprehensive, critical review of the natural history of ICAD by vessel in an attempt to assess the differences in disease specific to each of the vascular territories. Our assessment concludes that only minor differences exist between patients with different vessels affected in vessel-specific ICAD. We have found that middle cerebral artery disease confers a lower mortality than vessel-specific ICAD in other intracranial vessels, asymptomatic disease follows a more benign course than symptomatic disease, and that plaque progression or the detection of microemboli on transcranial Doppler may predict poor outcome. Given the expanding indications for treatment of ICAD and rapidly developing endovascular techniques to confront this disease, a thorough understanding of the natural history of ICAD aids the interventional neuroradiologist in determining when to treat and how to predict outcome in this patient population.
Novel electronic behavior driving NdNiO3 metal-insulator transition
M. H. Upton,Yongseong Choi,Jian Liu,D. Meyers,S. Middey,J. Chakhalian,Jong-Woo Kim,Philip J. Ryan
Physics , 2014,
Abstract: We present evidence that the metal-insulator transition (MIT) in a tensile strained NdNiO3 (NNO) film is facilitated by a redistribution of electronic density and neither requires Ni charge disproportionation nor symmetry change [1, 2]. Given epitaxial tensile strain in thin NNO films induces preferential occupancy of the $e_g$ $d_{x^2-y^2}$ orbital ($s_{3z^2-r^2}$) we propose the larger transfer integral of this orbital state with the O 2p mediates a redistribution of electronic density from the Ni atom. A decrease in Ni $d_{x^2-y^2}$ orbital occupation is directly observed by resonant inelastic x-ray scattering below the MIT temperature. Furthermore, an increase in Nd charge occupancy is measured by x-ray absorption at the Nd L3 edge. Both spin-orbit coupling and crystal field effects combine to break the degeneracy of the Nd 5d states shifting the energy of the Nd $e_g$ $d_{x^2-y^2}$ orbital towards the Fermi level allowing the A site to become an active acceptor during the MI transition. This work identifies the relocation of electrons from the Ni 3d to the Nd 5d orbitals across the MIT. We propose the insulating gap opens between the Ni 3d and O 2p resulting from Ni 3d electron localization mediated by charge loss. The transition seems neither purely Mott-Hubbard nor simple charge transfer.
From activity to learning: using cultural historical activity theory to model school library programmes and practices
E.M. Meyers
Information Research: an international electronic journal , 2007,
Abstract: Introduction. changes in educational policy and practice demand that we examine school library programmes from a new perspective. As a model that takes a developmental view of minds in context, Cultural Historical Activity Theory is particularly well suited to the study of school libraries and the learning that occurs therein. This paper focuses on the activity theoretic concepts of 'contradictions' and 'expansive learning' as they relate to the development of best practices. Method. Developmental Work Research was applied as a guiding methodology in an intervention study of six high school libraries in Washington State, USA. Library activity is illustrated from multiple perspectives using a triangulated, qualitative approach. Analysis. contradictions and tensions in the general school library activity system are identified, and an intervention was designed to facilitiate the development of expansive instruments. A case example illustrates a second level of analysis and specific points of intervention. Results. analysis reveals that the tensions and contradictions provide opportunities for expansive learning on the part of the teacher-Librarians. The research team can use practitioners' zones of proximal development to guide the alignment of library programme goals and practices. Conclusion. : some limitations and future promise of the framework and its application are discussed. The proposed activity theory toolkit suggest a new way of exploring the practices of teacher-librarians, incorporating research evidence, professional expertise, and reflective decision making.
E.M. Meyers
Scientia Militaria : South African Journal of Military Studies , 2012, DOI: 10.5787/12-1-638
Abstract: In order to adapt successfully to the military milieu, a soldier is required to arrange his personal values and disposition in accordance with the demands of that particular milieu. Selfdenial and total identification with the group are required of a good soldier. He must also always be correctly motivated as sincere belief in the purpose and necessity of a war is the most important component for the creating of esprit de corps, which in turn can greatly influence the soldier's performance on the battlefield. This article is a thoroughly researched attempt to analyse the soldiers' problems in adapting to a military milieu and to offer possible solutions to some of these problems.
E.M. Meyers
Scientia Militaria : South African Journal of Military Studies , 2012, DOI: 10.5787/16-5-446
Abstract: The most important function of the State President's Guard is that of acting as home guard for the State President and of acting as guard of honour at ceremonial occasions. Members of such a special guard not only had to meet specific requirements in the past. but even today they are subject to strict selection requirements. The uniform of the State President's Guard was changed recently. The new uniform, based on the current army uniform, replaces the old Republican model.
E.M. Meyers
Scientia Militaria : South African Journal of Military Studies , 2012, DOI: 10.5787/13-2-584
Abstract: The prerequisites for revolution can be divided into categories, according to the author of the article below. The most important categories are provocation, united public opinion, hope, a strong leader element and low morale. Examples are quoted of countries in which revolutions came to pass and the purpose of the article is to draw the attention of the reader to a certain pattern of occurrences and circumstances applicable to any country in which a revolutionary situation exists or has existed in the past.
E.M. Meyers.
Scientia Militaria : South African Journal of Military Studies , 2012, DOI: 10.5787/12-2-617
Abstract: Ontstaan van 'n verdedigingstelsel Die voorgeskiedenis van die Suid-Afrikaanse Weermag kan teruggevoer word tot aan die begin van die geskiedenis van die blanke volksplanting aan Tafelbaai. Reeds op 9 April 1652 het Jan van Riebeeck aan boord van die 'Drommedaris' 'n reglement vir soldate en offisiere uitgevaardig. Die bou van 'n fort, asook die feit dat die kommandeur van 'n garnisoenmag van ongeveer sewentig vergesel was, lewer bewys van die vaste wil van die opdraggewers om die jong nedersetting teen moontlike aanslae van buite, sowel as teen moontlike vyandiggesinde inboorlinge te verdedig.
E.M. Meyers
Scientia Militaria : South African Journal of Military Studies , 2012, DOI: 10.5787/16-5-447
Abstract: The primary function of the State President's Unit is to protect the head of state - not his person as is generally believed, but his authority over the state. Ironically, the ceremonial performances of the State President's Unit lead people to believe that they are only capable of doing drill exercises. However, upon investigating the training they receive during National Service, one soon changes one's opinion. The sentries are trained as soldiers who can protect their country against attacks from the outside, as well as against internal unrest. The ceremonial function is also of great importance and a high standard of training for the Unit, as home guard and as guard of honour, is maintained.
E.M. Meyers
Scientia Militaria : South African Journal of Military Studies , 2012, DOI: 10.5787/17-1-427
Abstract: An Institution such as the State President's Guard, has a long history and goes back to antiquity. Famous examples are the guards of King Xerxes of Persia and of more recent origin, the Swiss guard of the Vatican City. In the modern world these guards are the rule rather than the exception, in most states. The article below looks into the origin, functions and duties of inter alia the English Guard and the French Guard and the requirements for admission into these units. Also the origin and variations of the uniforms of these guards are dealt with. The female guards employed by the King of Siam deserve to be mentioned because of their unusualness and the author then proceeds to examine the Swiss Guard of the Vatican City. This article serves as an introduction to the articles that follow, dealing with the State President's unit in the Republic of South Africa.
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