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Biomedical subjects

T Yildirim

Publications and source records attributed to T Yildirim.

At least 19 recordsLinked to original sources
PubMed2006

Transition-metal-ethylene complexes as high-capacity hydrogen-storage media.

From first-principles calculations, we predict that a single ethylene molecule can form a stable complex with two transition metals (TM) such as Ti. The resulting TM-ethylene complex then absorbs up to ten hydrogen molecules, reaching to gravimetric storage capacity of approximately 14 wt %. Dimerization, polymerizations, and incorporation of the TM-ethylene complexes in nanoporous carbon materials are also discussed. Our results are quite remarkable and open a new approach to high-capacity hydrogen-storage materials discovery.

Journal Article↗
PubMed2006

Spin waves in the frustrated kagomé lattice antiferromagnet KFe3(OH)6(SO4)2.

The spin wave excitations of the S=5/2 kagomé lattice antiferromagnet KFe3(OH)6(SO4)2 have been measured using high-resolution inelastic neutron scattering. We directly observe a flat mode which corresponds to a lifted "zero energy mode," verifying a fundamental prediction for the kagomé lattice. A simple Heisenberg spin Hamiltonian provides an excellent fit to our spin wave data. The antisymmetric Dzyaloshinskii-Moriya interaction is the primary source of anisotropy and explains the low-temperature magnetization and spin structure.

Journal Article↗
PubMed2006

Double retroaortic left renal veins as a possible cause of pelvic congestion syndrome: imaging findings in two patients.

Pelvic congestion syndrome is characterized by chronic pelvic pain and varicose veins around the uterus and ovaries. We report two cases of double retroaortic left renal vein, associated with left-sided pelvic congestion syndrome, diagnosed by CT and confirmed by clinical findings and colour Doppler ultrasound. Double retroaortic left renal veins may be a contributing factor for the development of left pelvic congestion syndrome. This is the first report of double retroaortic left renal vein and associated pelvic congestion syndrome.

Chronic Disease↗
PubMed2005

Direct observation of hydrogen adsorption sites and nanocage formation in metal-organic frameworks.

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, molecules form unique interlinked high-symmetry nanoclusters with intermolecular distances as small as 3.0 Angstrom and H(2) uptake as high as 11 wt %. These results hold the key to optimizing metal-organic framework (MOF) materials for hydrogen storage applications and also suggest that MOFs can be used as templates to create artificial interlinked hydrogen nanocages with novel properties.

Journal Article↗
PubMed2005

Magnetically driven ferroelectric order in Ni3V2O8.

We show that long-range ferroelectric and incommensurate magnetic order appear simultaneously in a single phase transition in Ni3V2O8. The temperature and magnetic-field dependence of the spontaneous polarization show a strong coupling between magnetic and ferroelectric orders. We determine the magnetic symmetry using Landau theory for continuous phase transitions, which shows that the spin structure alone can break spatial inversion symmetry leading to ferroelectric order. This phenomenological theory explains our experimental observation that the spontaneous polarization is restricted to lie along the crystal b axis and predicts that the magnitude should be proportional to a magnetic order parameter.

Journal Article↗
PubMed2005

Titanium-decorated carbon nanotubes as a potential high-capacity hydrogen storage medium.

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 H2 adsorption is dissociative with no energy barrier while the 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. These results advance our fundamental understanding of dissociative adsorption of hydrogen in nanostructures and suggest new routes to better storage and catalyst materials.

Journal Article↗
PubMed2005

Value of computed tomography and magnetic resonance imaging for assessing severity of liver cirrhosis secondary to viral hepatitis.

PURPOSE: The aim of this study was to assess the value of abdominal CT and MRI in determining the severity of cirrhosis secondary to hepatitis compared to Child-Pugh classification. MATERIALS AND METHODS: The study included 23 patients who were clinically and histologically diagnosed with chronic liver disease secondary to viral hepatitis. Each patient underwent dynamic abdominal CT imaging and MRI within the same week. CT and MRI findings were retrospectively reviewed. The same parameters were used from the CT and the MR images for each patient. The parameters included liver volume index (posterior segment of the right lobe, medial and lateral segments of the left lobe), spleen volume index, ascites, portosystemic collaterals, contour irregularities of the liver and confluent fibrosis within the liver. The findings were compared with the patients' Child-Pugh grades. Multiple regression analysis was used for statistical analysis. RESULTS: On MRI, liver volume index (P = 0.0001), and ascites (P = 0.009) were strongly correlated with Child-Pugh grades. With CT, only ascites was correlated with Child-Pugh grades (P = 0.002). CONCLUSION: This study indicates that liver volume index on MRI, and ascites on CT and MRI are good indicators of clinical severity of cirrhosis secondary to hepatitis. To show the effect of the other parameters, more research is needed with larger patient groups.

Adult↗
PubMed2005

In vitro dentine permeability evaluation of HEMA-based (desensitizing) products using split-chamber model following in vivo application in the dog.

The aim of this study was to evaluate in vitro dentine permeability evaluation of 2-Hydroxyethyl methacrylate (HEMA)-based desensitizing products using split-chamber model following in vivo application in the dogs for three experimental time periods of 1 week, 1 month and 3 months. Buccal enamel of upper and lower canines of nine young dogs was removed and flat dentinal surface was obtained using a water-cooled diamond bur. The dentinal surface divided into four quarters, three experimental and a control. Health-Dent and Gluma Desensitizing agent and Single bond were applied to respective quarters of one tooth, according to manufacturers' instructions. The last quarters were left as control without any applications. For the each experimental period, 10 dentine samples from each group including control were used to measure the hydraulic conductance values. The dentine discs were placed pulp-side down in a split-chamber device in which the plastic spacers containing the rubber 0 rings have a surface area of 1 mm(2) and permeability was measured by fluid filtration. The data were expressed as hydraulic conductance (Lp). Differences in dentine permeability obtained for the desensitizing agents against the control were tested for statistical significance using Kruskal-Wallis one-way ANOVA and Bonferroni-adjusted Mann-Whitney U-tests. Differences in permeability in three time periods for each desensitizing agent were analysed using Friedman's anova and Wilcoxon signed rank tests. All desensitizing applications caused decreased Lp values compared with the control Lp value at the end of 1 week. In the 1-month samples, between the Lp values of Single bond and control, no statistical difference was found (P > 0.05). At the end of the 3-month period, the Gluma Desensitizing agent had the lowest the Lp value (P < 0.05). The result of this study is that the topical application of desensitizing agents led to decrease in dentine permeability in the dog model. The Gluma Desensitizing agent provide the more lasting tubule-occluding effect than the other material tested in this model.

Animals↗
PubMed2005

Case report: solid-pseudopapillary tumour of the pancreas associated with dorsal agenesis.

Solid-pseudopapillary tumour of the pancreas is a rare benign or low-grade malignant epithelial tumour; its association with pancreatic dorsal agenesis has been reported only once before. We present the radiological and histological findings of a case of pancreatic solid-pseudopapillary tumour associated with total pancreatic dorsal agenesis. A 49-year-old woman presented with abdominal pain radiating to the back for several months. Radiological findings showed absence of the dorsal pancreas and an 8 cm x 6 cm diameter tumour arising from the head of the pancreas. She underwent successful complete resection of the tumour. Histopathology revealed a diagnosis of solid-pseudopapillary tumour.

Back Pain↗
PubMed2005

Brachial artery pseudoaneurysm: a rare complication after haemodialysis therapy.

Haemodialysis patients carry a high risk of pseudoaneurysm due to inadvertent puncture of the brachial artery during venous cannulation for haemodialysis. Signs and symptoms are pulsatile mass and a systolic murmur. Complications are rupture, infection, haemorrhage, distal arterial insufficiency, venous thrombosis and neuropathy. Early diagnosis is essential to plan adequate treatment. Doppler US and angiography usually confirm the lesion accurately. Ultrasound guided compression, percutaneous injection of thrombin, endovascular covered stent exclusion, aneurysmectomy and surgical repair are different treatment options. We report clinical and radiological findings and treatment strategies in four dialysed patients who developed brachial artery pseudoaneurysms.

Adult↗
PubMed2005

Mucormycosis presenting with painful ophthalmoplegia.

Mucormycosis is a rare fungal infection that can involve the sino-orbito-cerebral region. Sino-orbito-cerebral mucormycosis is most common in patients who are immunocompromised or have diabetes mellitus, severe malnutrition or burns. This condition can be fatal if it is not diagnosed early and treated aggressively. This article presents 4 cases of mucormycosis, including 2 with orbital apex syndrome, 1 with cavernous sinus syndrome, and 1 with multiple cranial nerve involvement. All of the patients were presented with painful ophthalmoplegia. The predisposing factors for mucormycosis included diabetes mellitus (three patients) and chronic leukemia (one patient). In all cases, mucormycosis was diagnosed by examining endoscopic sinus drainage material and was treated with surgical debridement and amphotericin B. Two patients with central nervous system involvement died. The others have survived, but still exhibiting various neurologic abnormalities after aggressive treatment. Patients with mucormycosis rarely present with orbital apex syndrome. The possibility of mucormycosis should be investigated in any patient with painful ophthalmoplegia, and prompt otorhinolaryngologic examination is recommended to ensure rapid diagnosis and treatment.

Aged↗
PubMed2004

Competing magnetic phases on a kagomé staircase.

We present thermodynamic and neutron data on Ni3V2O8, a spin-1 system on a kagomé staircase. The extreme degeneracy of the kagomé antiferromagnet is lifted to produce two incommensurate phases at finite T--one amplitude modulated, the other helical--plus a commensurate canted antiferromagnet for T-->0. The H-T phase diagram is described by a model of competing first and second neighbor interactions with smaller anisotropic terms. Ni3V2O8 thus provides an elegant example of order from subleading interactions in a highly frustrated system.

Journal Article↗
PubMed2004

Intradural disc mimicking: a spinal tumor lesion.

STUDY DESIGN: A case report of intradural disc hernia mimicking an intradural extramedullary spinal tumor lesion in radiological evaluation. OBJECTIVE: To describe a lumbar intradural disc herniation with atypical radiological appearance and point out the role of contrast magnetic resonance imaging (MRI) of the lumbar spine. SETTING: Turkey. CASE REPORT: A 58-year-old man with suspected lumbar intradural mass and neurological involvement received L5 total laminectomy. L5 total laminectomy was performed, and on inspection dura was swollen and immobile. A longitudinal incision was made in the dura and an intradural-free disc fragment was removed. The patient's postoperative period was uneventful and he had full recovery in 3 months. CONCLUSIONS: Lumbar intradural disc rupture must be considered in the differential diagnosis of mass lesions causing nerve root or cauda equina syndromes. Contrast-enhanced MRI scans are useful to differentiate a herniated disc from a disc space infection or tumor. This case demonstrates the role and the importance of contrast MRI in the diagnosis of intradural disc herniation.

Diagnosis, Differential↗
PubMed2004

Value of color Doppler ultrasonography in the evaluation of orbital vascular flow in end-stage renal disease patients undergoing hemodialysis.

PURPOSE: To evaluate choroidal and retinal vascular flow dynamics by means of color Doppler ultrasonography in patients with end-stage renal disease undergoing hemodialysis and to compare these findings with healthy controls. MATERIAL AND METHODS: Color Doppler ultrasonography and spectral analysis of nasal and temporal posterior ciliary and central retinal artery flow of both eyes were performed in 20 patients (40 eyes) and 22 controls (44 eyes) to assess peak systolic flow velocity, end-diastolic flow velocity, and resistive indices (RI). Patients with hypertension, diabetes mellitus, and any cardiac pathology were not included in the study. A general ophthalmologic examination was performed in all patients and controls. RESULTS: The average peak-systolic and end-diastolic blood flow velocities of nasal (12.88 +/- 4.91/6.88 +/- 3.26) and temporal (15.22 +/- 9.59/6.41 +/- 3.97) posterior ciliary artery and central retinal artery (14.94 +/- 8.38/6.7 +/- 4.13) in patients were significantly higher than the corresponding values of the controls. The RI values of nasal (0.52 +/- 0.10) and temporal (0.58 +/- 0.12) posterior ciliary artery and central retinal artery (0.55 +/- 0.11) in patients with end-stage renal disease undergoing hemodialysis were significantly lower than in the controls. CONCLUSION: Choroidal and retinal blood flow velocities are higher and RI values for all three vessels lower in patients with end-stage renal disease undergoing hemodialysis compared to healthy controls. These alterations may be related to either increased choroidal blood flow or vasoconstriction of the proximal vessels.

Adolescent↗
PubMed2003

Magnetic resonance imaging of patients with cervicogenic headache.

Cervicogenic headache (CH) is a syndrome which is postulated to originate from nociceptive structures in the neck or head. The anatomical neck or head structures that are responsible for the pain in CH have not been clearly identified, but the pain in these patients probably originates from the structures of the cervical spine. In this study, cervical MRI were studied in 22 patients with cervicogenic headache and 20 control patients who did not have any disease which may effect the bone and muscle structures of cervical region. MRI imaging of cervical vertebra showed a disc bulging in 10 (45.4%) out of 22 patients with CH and in 9 (45.0%) of 20 controls (P > 0.05). The distribution of pathological lesions in patients and controls were not significantly different (P > 0.05). As a result, MRI may not be an adequate method to detect pathological findings underlying the aetiology of CH such as nerve roots, intervertebral joints and periosteum.

Adult↗