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Search Results: 1 - 10 of 1465 matches for " Konstantinos Arfanakis "
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Neuropathologic Correlates of Hippocampal Atrophy in the Elderly: A Clinical, Pathologic, Postmortem MRI Study
Robert J. Dawe, David A. Bennett, Julie A. Schneider, Konstantinos Arfanakis
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0026286
Abstract: The volume of the hippocampus measured with structural magnetic resonance imaging (MRI) is increasingly used as a biomarker for Alzheimer's disease (AD). However, the neuropathologic basis of structural MRI changes in the hippocampus in the elderly has not been directly assessed. Postmortem MRI of the aging human brain, combined with histopathology, could be an important tool to address this issue. Therefore, this study combined postmortem MRI and histopathology in 100 elderly subjects from the Rush Memory and Aging Project and the Religious Orders Study. First, to validate the information contained in postmortem MRI data, we tested the hypothesis that postmortem hippocampal volume is smaller in subjects with clinically diagnosed Alzheimer's disease compared to subjects with mild or no cognitive impairment, as observed in antemortem imaging studies. Subsequently, the relations of postmortem hippocampal volume to AD pathology, Lewy bodies, amyloid angiopathy, gross infarcts, microscopic infarcts, and hippocampal sclerosis were examined. It was demonstrated that hippocampal volume was smaller in persons with a clinical diagnosis of AD compared to those with no cognitive impairment (P = 2.6×10?7) or mild cognitive impairment (P = 9.6×10?7). Additionally, hippocampal volume was related to multiple cognitive abilities assessed proximate to death, with its strongest association with episodic memory. Among all pathologies investigated, the most significant factors related to lower hippocampal volume were shown to be AD pathology (P = 0.0018) and hippocampal sclerosis (P = 4.2×10?7). Shape analysis allowed for visualization of the hippocampal regions most associated with volume loss for each of these two pathologies. Overall, this investigation confirmed the relation of hippocampal volume measured postmortem to clinical diagnosis of AD and measures of cognition, and concluded that both AD pathology and hippocampal sclerosis affect hippocampal volume in old age, though the impacts of each pathology on the shape of the hippocampus may differ.
Faster cognitive decline in the years prior to MR imaging is associated with smaller hippocampal volumes in cognitively healthy older persons
Debra A. Fleischman,Lei Yu,Konstantinos Arfanakis,S. Duke Han,Patricia A. Boyle,David A. Bennett
Frontiers in Aging Neuroscience , 2013, DOI: 10.3389/fnagi.2013.00021
Abstract: Early identification of persons at risk for cognitive decline in aging is critical to optimizing treatment to delay or avoid a clinical diagnosis of mild cognitive impairment (MCI) or dementia due to Alzheimer's disease (AD). To accomplish early identification, it is essential that trajectories of cognitive change be characterized and associations with established biomarkers of MCI and AD be examined during the phase in which older persons are considered cognitively healthy. Here we examined the association of rate of cognitive decline in the years leading up to structural magnetic resonance imaging with an established biomarker, hippocampal volume. The sample comprised 211 participants of the Rush Memory and Aging Project who had an average of 5.5 years of cognitive data prior to structural scanning. Results showed that there was significant variability in the trajectories of cognitive change prior to imaging and that faster cognitive decline was associated with smaller hippocampal volumes. Domain-specific analyses suggested that this association was primarily driven by decline in working memory. The results emphasize the importance of closely examining cognitive change and its association with brain structure during the years in which older persons are considered cognitively healthy.
Systemic Inflammation in Non-Demented Elderly Human Subjects: Brain Microstructure and Cognition
Konstantinos Arfanakis, Debra A. Fleischman, Giorgia Grisot, Christopher M. Barth, Anna Varentsova, Martha C. Morris, Lisa L. Barnes, David A. Bennett
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0073107
Abstract: The purpose of this study was to test the hypothesis that higher levels of systemic inflammation in a community sample of non-demented subjects older than seventy years of age are associated with reduced diffusion anisotropy in brain white matter and lower cognition. Ninety-five older persons without dementia underwent detailed clinical and cognitive evaluation and magnetic resonance imaging, including diffusion tensor imaging. Systemic inflammation was assessed with a composite measure of commonly used circulating inflammatory markers (C-reactive protein and tumor necrosis factor-alpha). Tract-based spatial statistics analyses demonstrated that diffusion anisotropy in the body and isthmus of the corpus callosum was negatively correlated with the composite measure of systemic inflammation, controlling for demographic, clinical and radiologic factors. Visuospatial ability was negatively correlated with systemic inflammation, and diffusion anisotropy in the body and isthmus of the corpus callosum was shown to mediate this association. The findings of the present study suggest that higher levels of systemic inflammation may be associated with lower microstructural integrity in the corpus callosum of non-demented elderly individuals, and this may partially explain the finding of reduced higher-order visual cognition in aging.
Beyond the Dirac Phase Factor: Dynamical Quantum Phase-Nonlocalities in the Schrödinger Picture  [PDF]
Konstantinos Moulopoulos
Journal of Modern Physics (JMP) , 2011, DOI: 10.4236/jmp.2011.211156
Abstract: Generalized solutions of the standard gauge transformation equations are presented and discussed in physical terms. They go beyond the usual Dirac phase factors and they exhibit nonlocal quantal behavior, with the well-known Relativistic Causality of classical fields affecting directly the phases of wavefunctions in the Schrödinger Picture. These nonlocal phase behaviors, apparently overlooked in path-integral approaches, give a natural account of the dynamical nonlocality character of the various (even static) Aharonov-Bohm phenomena, while at the same time they seem to respect Causality. For particles passing through nonvanishing magnetic or electric fields they lead to cancellations of Aharonov-Bohm phases at the observation point, generalizing earlier semiclassical experimental observations (of Werner & Brill) to delocalized (spread-out) quantum states. This leads to a correction of previously unnoticed sign-errors in the literature, and to a natural explanation of the deeper reason why certain time-dependent semiclassical arguments are consistent with static results in purely quantal Aharonov-Bohm configurations. These nonlocalities also provide a remedy for misleading results propagating in the literature (concerning an uncritical use of Dirac phase factors, that persists since the time of Feynman’s work on path integrals). They are shown to conspire in such a way as to exactly cancel the instantaneous Aharonov-Bohm phase and recover Relativistic Causality in earlier “paradoxes” (such as the van Kampen thought-experiment), and to also complete Peshkin’s discussion of the electric Aharonov-Bohm effect in a causal manner. The present formulation offers a direct way to address time-dependent single- vs double-slit experiments and the associated causal issues—issues that have recently attracted attention, with respect to the inability of current theories to address them.
Classical Quantum Field Theory Based on the Hypothesis of the Absolute Reference System  [PDF]
Konstantinos Patrinos
Journal of Applied Mathematics and Physics (JAMP) , 2019, DOI: 10.4236/jamp.2019.74052
Abstract: The quantum field theory based on the hypothesis of the absolute reference system is a classical non-relativistic theory, which is compatible with current quantum theory. This conclusion arises when one compares the theoretical results of quantum electrodynamics using the basic principles of this hypothesis. Wave equation, which replaces this of Schrodinger, is the classical wave equation of a peculiar electromagnetic wave, derived from the study of particle structure.
The Physics of an Absolute Reference System  [PDF]
Konstantinos Patrinos
Journal of Applied Mathematics and Physics (JAMP) , 2019, DOI: 10.4236/jamp.2019.73033
Abstract: The hypothesis of the absolute reference system, unlike the existing physics theories, is not based on the concept of relativity (that is, it is not based on a relativistic description like Galileo’s relativity or Einstein’s theory of relativity). The absolute reference system is the framework of material in which any activity in the universe has begun. Also, each inertial reference system is accompanied by a peculiar electromagnetic wave due to the structure of matter. The physics of the absolute system of reference is based on three basic principles. The first of these principles is that the electromagnetic field quantitative estimates are made in the inertial reference system of the source of the electromagnetic field. The second principle is that the basic constituent of matter is “bound photons, which make up the internal structure of the elementary particles. The third principle is that the framework of material of an inertial system undergoes a contraction of length which is a real physical contraction and a corresponding real change in “time flow, not due to the geometry of space-time, but is due to the internal operation of the micro-structure of matter. These principles have the effect of changing the relativistic physical magnitudes, such as velocity, momentum and kinetic energy, into physical magnitudes described as absolute. This theory is consistent with experimental data so far and provides satisfactory answers to physics problems such as dark matter, particle physics experiments to confirm the dynamics, interpretation of experimental results of measurement of neutrinos velocity that are incompatible with the relativity, and magnetic induction experiments which are not explained by the classical electromagnetic theory.
Polynomial-Based Evaluation of the Impact of Aperture Phase Taper on the Gain of Rectangular Horns  [PDF]
Konstantinos B. Baltzis
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2010, DOI: 10.4236/jemaa.2010.27055
Abstract: The aperture phase taper due to quadratic phase errors in the principal planes of a rectangular horn imposes signifi-cant constraints on the on-axis far-field gain of the horn. The precise calculation of gain reduction involves Fresnel integrals; therefore, exact results are obtained only from numerical methods. However, in horns’ analysis and design, simple closed-form expressions are often required for the description of horn-gain. This paper provides a set of simple polynomial approximations that adequately describe the gain reduction factors of pyramidal and sectoral horns. The proposed formulas are derived using least-squares polynomial regression analysis and they are valid for a broad range of quadratic phase error values. Numerical results verify the accuracy of the derived expressions. Application examples and comparisons with methods in the literature demonstrate the efficacy of the approach.
Informal Financing of Small – Medium Enterprise Sector: The Case of Greece  [PDF]
Panagiotis Petrakis, Konstantinos Eleftheriou
Journal of Service Science and Management (JSSM) , 2009, DOI: 10.4236/jssm.2009.24045
Abstract: In this paper, we attempt to find a “channel” through which Greek economy can exhibit a relative “resistance” in a credit crunch. For this purpose, we specify an error correction model so as to test the relationship between corporate bank loans and commercial papers comprised of post-dated cheques and bills of exchange. The results show that corporate bank loans and cheques - bills of exchange are substitutes. This finding combined with the fact that in Greece, the issuance of these papers is positively connected with the informal economic activity which in turn rises during economic downturns, has a strong economic implication regarding the ability of Greek economy to partly “amortize” the shocks connected with the current financial crisis.
Presentation of a Rare Case of Bilateral Lumbar Synovial Cysts  [PDF]
Konstantinos Violaris, Maria Karakyriou
Open Journal of Modern Neurosurgery (OJMN) , 2012, DOI: 10.4236/ojmn.2012.22006
Abstract: Purpose: To report a quite rare case of bilateral symptomatic synovial cysts of the lumbar spine. Surgical resection is usually the cure for this condition. Methods: A 65 year old female patient came to our department, complaining for severe lumbar and sciatic pain. MRI and CT were used to diagnose bilateral synovial cysts. Because of the intensity of symptoms, she was subjected to surgery. Laminectomy and cyst resection were performed. Results: The patient showed complete resolution of pain after the resection of the cysts. Conclusion: Although rare, bilateral synovial cysts may be the cause of severe lumbar pain. In cases of failure of conservative treatment, surgical resection offers good results.
Poly(Vinyl Alcohol)-Infiltrated Carbon Nanotube Carpets  [PDF]
Konstantinos G. Dassios
Materials Sciences and Applications (MSA) , 2012, DOI: 10.4236/msa.2012.39096
Abstract: Carbon nanotube-polymer interaction is one of the key factors controlling the mechanical properties in composite and hybrid systems of such constituents. The current study reports a series of direct observations of substantial polymer sheathing phenomena on millimeters-high carpets of vertically aligned tubes infiltrated by Poly(vinyl alcohol) (PVA). SEM and TEM images of the composite’s fracture surface revealed that sheathing was extensive and universal over the carpet’s volume and did not influence the morphology, alignment or physical characteristics of the tubes. A significant increase in the tubes’ diameters due to PVA coating was measured. Thermogravimetric analysis results were compatible with a crystallinity increase of the polymer phase due to the presence of CNTs, indicating the potential of CNTs in nucleating polymer crystallinity. Potential applications of the nanocomposite are discussed.
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