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Search Results: 1 - 10 of 1640 matches for " Christos Panagopoulos "
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Superfluid density as a guide to optimal superconductivity in doped low dimensional antiferromagnets
Christos Panagopoulos
Physics , 2006,
Abstract: Following the direct observation of abrupt changes in the superconducting ground state in doped low dimensional antiferromagnets, we have identified a phase transition where superconductivity is optimal. The experiments indicate the presence of a putative quantum critical point associated with the emergence of a glassy state. This mechanism is argued to be an intrinsic property and as such largely independent of material quality and the level of disorder.
Two types of superconducting domes in unconventional superconductors
Tanmoy Das,Christos Panagopoulos
Physics , 2015,
Abstract: Over the past few decades, several new classes of superconductors have been discovered that appear neither identical to the conventional superconductors, nor related to each other. These new families, collectively called unconventional superconductors, often host a superconducting (SC) dome when the magnetic order is suppressed with various tuning parameters. Uncovering the origin of unconventional superconductivity is often plagued by the overwhelming material dependent properties and their varying normal states. In this article, we deliver a comprehensive analysis of the SC properties and phase diagrams across several families of unconventional superconductors, including the copper-oxides, heavy-fermions, organics and the recently discovered iron-pnictides, iron-chalcogenides, and oxybismuthides. We find that all these families possess two types of SC domes, with lower and higher superconducting transition temperatures Tc, both unconventional but with distinct SC and normal state properties. The lower Tc dome arises with or without a quantum critical point (QCP), but not always associated with a non-Fermi liquid (NFL) background. On the contrary, the higher-Tc dome stems from a NFL or strange metal phase without an intervening phase transition or QCP. The two domes appear either fully separated in the phase diagram, merged into one or to arise independently owing to peculiarities in the respective normal states. We also introduce an experimental tool, namely multiple tuning (such as disorder, pressure or magnetic field in addition to doping and vice versa) to separate the two SC domes and study the relationship between QCP, NFL, and superconductivity. Our analysis suggests NFL physics may be a generic route to higher-Tc superconductivity.
Corrosion of Nanocrystalline Ni-W Coated Copper  [PDF]
Christos N. Panagopoulos, Georgios D. Plainakis, Maria G. Tsoutsouva
Journal of Surface Engineered Materials and Advanced Technology (JSEMAT) , 2015, DOI: 10.4236/jsemat.2015.52007
Abstract: The present study is dealing with the corrosion of copper coated with nanocrystalline nickeltungsten coating. Different plating bath compositions and conditions were used in order to produce nickel-tungsten coatings of different tungsten content 30%, 40% and 50% wt, with a thickness of 20 μm. The corrosion resistance of nickel-tungsten alloy coated copper was examined by a potentiodynamic polarisation technique in NaCl solution (0.03 M, 0.3 M and 1 M) as a function of pH (3, 7, 10) and temperature (7°C, 30°C, 40°C) of the solution. It has been found that the pH value did not seem to affect the corrosion behaviour of the coated specimen remarkably, while the increase of solution temperature increased the corrosion rate of the coated copper specimen. It was finally confirmed that the corrosion products mainly consisted of tungsten and nickel oxides.
Effects of the CuO chains on the anisotropic penertration depth of YBa2Cu4O8
Christos Panagopoulos,Jeffery L Tallon,Tao Xiang
Physics , 1998,
Abstract: The temperatuer dependence of the magnetic penetration depth of grain aligned YBa2Cu4O8 has been measured along the ab plane and c-axis. Both $\lambda_ab$ and $\lambda_c$ vary as \sqrt{T} up to 0.4Tc implying a square root density of states at low energy. The results are discussed in terms of a proximity model of alternating stacked superconducting and normal layers
Holographic quantum criticality and strange metal transport
Bom Soo Kim,Elias Kiritsis,Christos Panagopoulos
Physics , 2010, DOI: 10.1088/1367-2630/14/4/043045
Abstract: A holographic model of a quantum critical theory at a finite but low temperature, and finite density is studied. The model exhibits non-relativistic z=2 Schr\"odinger symmetry and is realized by the Anti-de-Sitter-Schwarzschild black hole in light-cone coordinates. Our approach addresses the electrical conductivities in the presence or absence of an applied magnetic field and contains a control parameter that can be associated to quantum tuning via charge carrier doping or an external field in correlated electron systems. The Ohmic resistivity, the inverse Hall angle, the Hall coefficient and the magnetoresistance are shown to be in good agreement with experimental results of strange metals at very low temperature. The holographic model also predicts new scaling relations in the presence of a magnetic field.
Late Prosthetic Shoulder Hemiarthroplasty after Failed Management of Complex Proximal Humeral Fractures
A. Panagopoulos,P. Tsoumpos,K. Evangelou,Christos Georgiou
Advances in Orthopedics , 2013, DOI: 10.1155/2013/403580
Abstract:
Late Prosthetic Shoulder Hemiarthroplasty after Failed Management of Complex Proximal Humeral Fractures
A. Panagopoulos,P. Tsoumpos,K. Evangelou,Christos Georgiou,I. Triantafillopoulos
Advances in Orthopedics , 2013, DOI: 10.1155/2013/403580
Abstract: Background. The purpose of this study was to report our experience with shoulder hemiarthroplasty in the context of old trauma. Methods. 33 patients with failed treatment for a complex proximal humeral fracture underwent prosthetic hemiarthroplasty. There were 15 men and 18 women with a mean age of 58.1 years. The average period from initial treatment was 14.9 months. Sequelae included 11 malunions, 4 nonunions, 15 cases with avascular necrosis (AVN) and 3 neglected posterior locked dislocations. Follow up investigation included radiological assessment and clinical evaluation using the Constant score and a visual analogue pain scale. Results. After a mean follow up of 82.5 months the median Constant score was 75.7 points, improved by 60% in comparison to preoperative values. Greater tuberosity displacement, large cuff tears and severe malunion were the factors most affected outcome. No cases of stem loosening or severe migration were noted. 60% of the patients were able to do activities up to shoulder level compared with 24% before reconstruction. Conclusions. Late shoulder hemiarthroplasty is technically difficult and the results are inferior to those reported for acute humeral head replacement, nonetheless remains a satisfactory reconstructive option when primary treatment fails. 1. Introduction Shoulder hemiarthroplasty is a technically challenging procedure which can predictably restore shoulder-level function in patients with 4-part fractures, some 3-part fractures, fracture dislocations, head-splitting fractures, and impaction fractures of the humeral head with involvement of more than 50% of the articular surface [1–4]. Early surgical intervention within 2 weeks postinjury, accurate tuberosity reconstruction, and appropriate height and retroversion of the prosthesis are the factors with the greatest impact on functional outcome [5–8]. In contrast, outcomes of internal fixation [9, 10] and nonoperative treatment [11, 12] for these complex fractures are quite controversial, with the initial management considered critically important. Krappinger et al. [13] showed in a recent study that multifragmentary fracture patterns in old patients with low local BMD are prone for fixation failure. Revision osteosynthesis or late prosthetic shoulder arthroplasty in these complex fractures is fraught with complications, and functional results are usually disappointing [14, 15]. Bone loss, malunion, ectopic ossification, avascular necrosis, associated rotator cuff tears, and severe contractions of soft tissues are some of the factors that prevent appropriate
Interface superconductivity: History, development and prospects
Juan Pereiro,Alexander Petrovic,Christos Panagopoulos,Ivan Bo?ovi?
Physics , 2011,
Abstract: The concept of interface superconductivity was introduced over 50 years ago. Some of the greatest physicists of that time wondered whether a quasi-two-dimensional (2D) superconductor can actually exist, what are the peculiarities of 2D superconductivity, and how does the reduced dimensionality affect the critical temperature (Tc). The discovery of high-temperature superconductors, which are composed of coupled 2D superconducting layers, further increased the interest in reduced dimensionality structures. In parallel, the advances in experimental techniques made it possible to grow epitaxial 2D structures with atomically flat surfaces and interfaces, enabling some of the experiments that were proposed decades ago to be performed finally. Now we know that interface superconductivity can occur at the junction of two different materials (metals, insulators, semiconductors). This phenomenon is being explored intensely; it is also exploited as a means to increase Tc or to study quantum critical phenomena. This research may or may not produce a superconductor with a higher Tc or a useful superconducting electronic device but it will likely bring in new insights into the physics underlying high-temperature superconductivity.
Prevalence of self-reported hypertension and its relation to dietary habits, in adults; a nutrition & health survey in Greece
Christos Pitsavos, George A Milias, Demosthenes B Panagiotakos, Dimitra Xenaki, George Panagopoulos, Christodoulos Stefanadis
BMC Public Health , 2006, DOI: 10.1186/1471-2458-6-206
Abstract: A random-digit dialed telephone survey. Based on a multistage, stratified sampling, 5003 adults (18 – 74 yr) participated (men: 48.8%, women: 51.2%). All participants were interviewed via telephone by trained personnel who used a standard questionnaire. The questionnaire included demographic and socioeconomic characteristics, medical history, lifestyle habits and nutritional assessment.The prevalence of self-reported hypertension was 13.3% in men and 17.7% in women (P < 0.001). Furthermore, women reported higher values of systolic blood pressure (180 ± 27 mmHg) than men (169 ± 24 mmHg). Positive relationships were found between hypertension status and the prevalence of the rest investigated health conditions (i.e. hypercholesterolaemia, diabetes mellitus, renal failure and obesity). Nutritional assessment showed that consumption of fish, fruits and juices, cereals, and low fat milk and yogurt was significantly higher among hypertensive subjects while the opposite was observed for food items as red meat, pork, egg, pasta and rice, full fat dairy products and desserts.Hypertension seems to be a serious public health problem in Greece. It is encouraging that hypertensives may have started adopting some more healthy nutritional behaviour compared to normotensive ones. However, they can gain significant benefits regarding to blood pressure control, if they increase the level of compliance with dietary recommendations.High blood pressure [1] has been identified as a major risk factor for stroke, congestive heart failure, renal disease and myocardial infarction [2,3]. According to World Health Organization the number of people with high blood pressure levels, worldwide, is estimated to be about 600 million and the annual mortality attributable to hypertension is estimated to be about 7.14 million deaths. As far as the European developed countries is concerned, it is estimated that hypertension is responsible for about 17% of total annual mortality or in other words, for ap
Prevalence of self-reported hypercholesterolaemia and its relation to dietary habits, in Greek adults; a national nutrition & health survey
George A Milias, Demosthenes B Panagiotakos, Christos Pitsavos, Dimitra Xenaki, George Panagopoulos, Christodoulos Stefanadis
Lipids in Health and Disease , 2006, DOI: 10.1186/1476-511x-5-5
Abstract: Cross sectional survey. Based on a multistage sampling, 5003 adults (18 – 74 yr) were enrolled (men: 48.8%, women: 51.2%). All participants were interviewed by trained personnel who used a standard questionnaire. The questionnaire included demographic and socioeconomic characteristics, medical history, lifestyle habits and nutritional assessment.The prevalence of self-reported hypercholesterolaemia was 16.4% in men and 21.8% in women (P < 0.001). Hypercholesterolaemic status was positively associated with the prevalence of hypertension, diabetes mellitus, renal failure, obesity and physical inactivity, and inversely with the prevalence of smoking. The analysis of reported food consumption patterns showed that consumption of fish, fruits and juices, cereals, and low fat milk and yogurt was significantly higher among hypercholesterolaemic participants while the opposite was observed for food items as red meat, pork, egg, full fat dairy products and desserts.Hypercholesterolaemia seems to affect a large part of Greek population. It is hopeful that hypercholesterolaemics may have started adopting some more healthy nutritional behaviour compared to normocholesterolaemic ones.Cardiovascular disease is the leading cause of death worldwide affecting millions of people in both developed and developing countries. In particular, in most European countries cardiovascular disease contributes about 40% to all cause mortality [1]. Accumulating evidence coming up from numerous studies [2-6], have revealed the strong causal role of hypercholesterolaemia on the progression of atherosclerosis and subsequently on the development of cardiovascular disease. According to the World Health Organization (WHO) it is estimated that high cholesterol causes around a third of all cardiovascular disease worldwide, and that 105 million people in the USA have cholesterol levels that are a cardiovascular risk [7].It should be noted that the strength of the relationship between hypercholesterolaemia a
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