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Search Results: 1 - 10 of 154907 matches for " Tülin YILDIRIM "
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Clinical Manifestations and MR Imaging Features In Hypothalamic Hamartomas
?zlem ALKAN,Osman KIZILKILI?,Tuba KARSANTI?Zü,Tülin YILDIRIM
Journal of Neurological Sciences , 2009,
Abstract: Hypothalamic hamartomas (HH) are rare non-neoplastic congenital malformations. The aims of this study are to demonstrate the brain MR findings and clinical manifestations in children with HH and the literature is reviewed. We have evaluated 6 children with HH diagnosed by brain MR imaging. We analyzed age at seizure onset, seizure types, neuropsychological assessment, and the presence of precocious puberty, electroencephalogram and MR findings. Among 6 HH patients, 2 manifested precocious puberty, 2 had experienced seizures, and 1 presented with both precocious puberty and seizures, and 1 presented with hyperactivity. MR imaging showed hypothalamic mass that was isointense to brain parenchyma on T1- weighted images and isointense-or hyperintense on T2-weighted images, without contrast enhancement. The size of the lesions does not change in the course of follow-up. Typical clinical presentation, peculiar location and MR imaging features strongly favour the HH diagnosis. Accurate diagnosis and classification is important for the selection of treatment modality.
Late Onset Poststroke Seizures
Ba?ak Karakurum G?KSEL,Mehmet KARATA?,Meliha TAN,,Tülin YILDIRIM
Journal of Neurological Sciences , 2005,
Abstract: The most common cause of seizures is cerebrovascular disease in elderly population. Late onset seizures are not investigated as well as early onset seizures in patients with stroke. There is no common consensus about clinical, electrophysiological and radiological features of these seizures. In this study, 55 patients with late onset seizure who had stroke history were investigated. The 49 % of patients were women, the mean ages of patients were 63.9±9.2 years. The mean of duration between stroke and the first seizure was 30.4±36.8 months and the mean of following time was 14±13 months. The 89% of patients ischemic stroke and 11% of patients had hemorrhagic stroke. The lesion localizations were cortical in 17 (30.9%) patients, subcortical in 8 (14.5%) and cortico-subcortical in 29 (52.7%). As a result 84 % patients’ lesions were cortical localization. There were partial seizure in 39 (%70.9) patients, generalized tonic-clonic seizure in 16 (29.1%) patients. 43 (78%) patients had no seizure during antiepileptic therapy. 7 (12.7%) patients had seizure after beginning antiepileptic drug due to stopping drug, low blood level of drug and ineffectiveness of drug. 5 (9%) patients had not been given drug because of first seizure and no seizure during follow-up. In conclusion, the late onset poststroke seizures seem frequently in ischemic stroke, the reccurence rate was high and partial type seizures were more common than generalized and cortical localization was seen frequently. On the other hand, this condition has good prognosis.
Origin of the ~150 K Anomaly in LaOFeAs; Competing Antiferromagnetic Superexchange Interactions, Frustration, and Structural Phase Transition
T. Yildirim
Physics , 2008, DOI: 10.1103/PhysRevLett.101.057010
Abstract: From first principles calculations we find that the nearest and next nearest neighbor superexchange interactions between Fe ions in LaOFeAs are large, antiferromagnetic (AF), and give rise to a frustrated magnetic ground state which consists of two interpenerating AF square sublattices with M(Fe)=0.48$\mu_B$. The system lowers its energy further by removing the frustration via a structural distortion. These results successfully explain the magnetic and structural phase transitions in LaOFeAs recently observed by neutron scattering. The presence of competing strong antiferromagnetic exchange interactions and the frustrated ground state suggest that magnetism and superconductivity in doped LaOFeAs may be strongly coupled, much like in the high-T$_c$ cuprates.
Nature of Magnetic Interactions and Inelastic Neutron Scattering as a Probe of Magnetic Excitations in Iron-Pnictide Superconductors
T. Yildirim
Physics , 2008,
Abstract: This submission has been withdrawn by the arXiv admins because it is an abstract only, which is against arXiv policy.
The Unprecedented Giant Coupling of Fe-spin State and the As-As Hybridization in Iron-Pnictide
T. Yildirim
Physics , 2008, DOI: 10.1103/PhysRevLett.102.037003
Abstract: From first principles calculations we unravel surprisingly strong interactions between arsenic ions in iron-pnictides, the strength of which is controlled by the Fe-spin state. Reducing the Fe-magnetic moment, weakens the Fe-As bonding, and in turn, increases As-As interactions, causing giant reduction in the c-axis. For CaFe$_2$As$_2$ system, this reduction is as large as 1.4 \AA. Since the large c-reduction has been recently observed only under high-pressure\cite{cTphase}, our results suggest that the iron magnetic moment should be present in Fe-pnictides at all times at ambient pressure. Finally, the conventional electron-phonon coupling in the collapsed phase of CaFe$_2$As$_2$ gives a maximum $T_c$ of 0.6 K and can not explain the $\sim12$ K superconductivity observed in some experiments. Implications of these findings on the mechanism of superconductivity in iron-pnictides are discussed.
Fungi in the atmospheric air of anakkale province in Turkey
T Suerdem, I Yildirim
African Journal of Biotechnology , 2009,
Abstract: No
Titanium-decorated carbon nanotubes: a potential high-capacity hydrogen storage medium
T. Yildirim,S. Ciraci
Physics , 2005, DOI: 10.1103/PhysRevLett.94.175501
Abstract: We report a first-principles study, which demonstrates that a single Ti atom coated on a single-walled nanotube (SWNT) binds up to four hydrogen molecules. The first H$_2$ adsorption is dissociative with no energy barrier while other three adsorptions are molecular with significantly elongated H-H bonds. At high Ti coverage we show that a SWNT can strongly adsorb up to 8-wt% hydrogen. The system is quite stable and exhibits associative desorption upon heating, a requirement for reversible storage. These results advance our fundamental understanding of dissociative adsorption of hydrogen in nanostructures and suggest new routes to better storage and catalyst materials.
Lattice Dynamics of Metal-Organic Frameworks (MOFs): Neutron Inelastic Scattering and First-Principles Calculations
W. Zhou,T. Yildirim
Physics , 2006, DOI: 10.1103/PhysRevB.74.180301
Abstract: By combining neutron inelastic scattering (NIS) and first-principles calculations, we have investigated the lattice dynamics of MOF5. The structural stability of MOF5 was evaluated by calculating the three cubic elastic constants. We find that the shear modulus, c44 = 1.16 GPA, is unusually small, while two other moduli are relatively large (i.e. c11 = 29.42 GPa and c12 = 12.56 GPa). We predict that MOF5 is very close to structural instability and may yield interesting new phases under high pressure and strain. The phonon dispersion curves and phonon density of states were directly calculated and our simulated NIS spectrum agrees very well with our experimental data. Several interesting phonon modes are discussed, including the softest twisting modes of the organic linker.
Charge and Spin Ordering in the Mixed Valence Compound LuFe2O4
A. B. Harris,T. Yildirim
Physics , 2008, DOI: 10.1103/PhysRevB.81.134417
Abstract: Landau theory and symmetry considerations are invoked to give a unified treatment of charge and spin ordering in the mixed valence compound LuFe2O4. In particular, the unusual evolution of charge ordering correlations can be explained by invoking phonon mediated interactions.
Direct Observation of Hydrogen Adsorption Sites and Nano-Cage Formation in Metal-Organic Frameworks (MOF)
T. Yildirim,M. R. Hartman
Physics , 2005, DOI: 10.1103/PhysRevLett.95.215504
Abstract: The hydrogen adsorption sites in MOF5 were determined using neutron powder diffraction along with first-principles calculations. The metal-oxide cluster is primarily responsible for the adsorption while the organic linker plays only a secondary role. Equally important, at low temperatures and high-concentration, H2 molecules form unique interlinked high-symmetry nano-clusters with intermolecular distances as small as 3.0 Ang. and H2-uptake as high as 10-wt%. These results hold the key to optimizing MOF materials for hydrogen storage applications and also suggest that MOFs can be used as templates to create artificial interlinked hydrogen nano-cages with novel properties.
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