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Search Results: 1 - 10 of 429016 matches for " B. S. Kandemir "
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Chiral Polaron Formation in Graphene
B. S. Kandemir
Physics , 2012,
Abstract: A theoretical investigation of the possible existence of the chiral polaron formation in graphene is reported. We present an analytical method to calculate the ground-state of the electron-phonon system within the framework of the Lee-Low and Pines theory. On the basis of our model, the influence of electron-optical phonon interaction onto the graphene electronic spectrum is examined. In this paper, we only considered doubly degenerate optical phonon modes of E_2g symmetry near the zone center Gamma. We show analytically that the energy dispersions of both valance and conduction bands of the pristine graphene differ significantly than those obtained through the standard electron self energy calculations due to the electron-phonon interactions. Furthermore, we prove that the degenerate band structure of the graphene promote the chiral polaron formation.
Intrinsic Spin-Orbit Interaction in Graphene
B. S. Kandemir
Physics , 2012,
Abstract: In graphene, we report the first theoretical demonstration of how the intrinsic spin orbit interaction can be deduced from the theory and how it can be controlled by tuning a uniform magnetic field, and/or by changing the strength of a long range Coulomb like impurity (adatom), as well as gap parameter. In the impurity context, we find that intrinsic spin-orbit interaction energy may be enhanced by increasing the strength of magnetic field and/or by decreasing the band gap mass term. Additionally, it may be strongly enhanced by increasing the impurity strength. Furthermore, from the proposal of Kane and Mele [Phys. Rev. Lett. 95, 226801 (2005)], it was discussed that the pristine graphene has a quantized spin Hall effect regime where the Rashba type spin orbit interaction term is smaller than that of intrinsic one. Our analysis suggest the nonexistence of such a regime in the ground state of flat graphene.
Variational Approach for the Effects of Periodic Modulations on the Spectrum of Massless Dirac Fermion
B. S. Kandemir,A. Mogulkoc
Physics , 2009, DOI: 10.1140/epjb/e2010-00051-4
Abstract: In the variational framework, we study the electronic energy spectrum of massless Dirac fermions of graphene subjected to one-dimensional oscillating magnetic and electrostatic fields centered around a constant uniform static magnetic field. We analyze the influence of the lateral periodic modulations in one direction, created by these oscillating electric and magnetic fields, on Dirac like Landau levels depending on amplitudes and periods of the field modulations. We compare our theoretical results with those found within the framework of non-degenerate perturbation theory. We found that the technique presented here yields energies lower than that obtained by the perturbation calculation, and thus gives more stable solutions for the electronic spectrum of massless Dirac fermion subjected to a magnetic field perpendicular to graphene layer under the influence of additional periodic potentials.
Boundaries of Subcritical Coulomb Impurity Region in Gapped Graphene
B. S. Kandemir,A. Mogulkoc
Physics , 2009, DOI: 10.1140/epjb/e2010-00116-4
Abstract: The electronic energy spectrum of graphene electron subjected to a homogeneous magnetic field in the presence of a charged Coulomb impurity is studied analytically within two-dimensional Dirac-Weyl picture by using variational approach. The variational scheme we used is just based on utilizing the exact eigenstates of two-dimensional Dirac fermion in the presence of a uniform magnetic field as a basis for determining analytical energy eigenvalues in the presence of an attractive/repulsive charged Coulomb impurity. This approach allows us to determine under which conditions bound state solutions can or can not exist in gapped graphene in the presence of magnetic field. In addition, the effects of uniform magnetic field on the boundaries of subcritical Coulomb impurity region in the massless limit are also analyzed. Our analytical results show that the critical impurity strength decreases with increasing gap/mass parameter, and also that it increases with increasing magnetic field strength. In the massless limit, we investigate that the critical Coulomb coupling strength is independent of magnetic field, and its upper value for the ground-state energy is 0.752.
Zone-Boundary Phonon Induced Mini Band Gap Formation in Graphene
B. S. Kandemir,A. Mogulkoc
Physics , 2012, DOI: 10.1016/j.ssc.2013.09.012
Abstract: We investigate the effect of electron- $\mathrm{A}_{1g}$ phonon coupling on the gapless electronic band dispersion of the pristine graphene. The electron-phonon interaction is introduced through a Kekul\'{e}-type distortion giving rise to inter-valley scattering between K and K' points in graphene. We develop a Fr\"ohlich type Hamiltonian within the continuum model in the long wave length limit. By presenting a fully theoretical analysis, we show that the interaction of charge carriers with the highest frequency zone-boundary phonon mode of $% \mathrm{A}_{1g}$-symmetry induces a mini band gap at the corners of the two-dimensional Brillouin zone of the graphene. Since electron-electron interactions favor this type of lattice distortion, it is expected to be enhanced, and thus its quantitative implications might be measurable in graphene.
Two-particle Wigner functions in a one-dimensional Calogero-Sutherland potential
A. Tegmen,T. Altanhan,B. S. Kandemir
Physics , 2007, DOI: 10.1140/epjd/e2006-00221-1
Abstract: We calculate the Wigner distribution function for the Calogero-Sutherland system which consists of harmonic and inverse-square interactions. The Wigner distribution function is separated out into two parts corresponding to the relative and center-of-mass motions. A general expression for the relative Wigner function is obtained in terms of the Laguerre polynomials by introducing a new identity between Hermite and Laguerre polynomials.
Exogenous group G Streptococcus endophthalmitis following intravitreal ranibizumab injection
Kugu S, Sevim MS, Kaymak NZ, Erdogan G, Kandemir B, Dogan OK
Clinical Ophthalmology , 2012, DOI: http://dx.doi.org/10.2147/OPTH.S31721
Abstract: genous group G Streptococcus endophthalmitis following intravitreal ranibizumab injection Case report (1284) Total Article Views Authors: Kugu S, Sevim MS, Kaymak NZ, Erdogan G, Kandemir B, Dogan OK Published Date August 2012 Volume 2012:6 Pages 1399 - 1402 DOI: http://dx.doi.org/10.2147/OPTH.S31721 Received: 12 March 2012 Accepted: 19 May 2012 Published: 28 August 2012 Suleyman Kugu,1 Mehmet Sahin Sevim,2 Nilufer Zorlutuna Kaymak,1 Gurkan Erdogan,3 Baran Kandemir,1 Omer Kamil Dogan4 1Lutfi Kirdar Kartal Training and Research Hospital, Eye Clinic, Istanbul, 2Haydarpasa Numune Training and Research Hospital, Eye Clinic, Istanbul, 3Umraniye Training and Research Hospital, Eye Clinic, Istanbul, 4World Eye Hospital, Eye Clinic, Istanbul, Turkey Abstract: We report a case of group G Streptococcus endophthalmitis following an intravitreal ranibizumab injection for a choroidal neovascular membrane. Pars plana vitrectomy was applied for endophthalmitis and group G Streptococcus cultures were isolated in the vitreous samples taken from the patient. Twenty-four hours following pars plana vitrectomy the patient underwent myocardial infarction and cardiac arrest. To our knowledge this is the first reported case of group G Streptococcus endophthalmitis following an intravitreal injection.
Coincidentally determined floating right ventricular thrombus in a patient with coronary artery disease
?zer Kandemir,Mustafa Büyükate?,Erol Aktun?,S. Ak?n Turan
Anadolu Kardiyoloji Dergisi , 2009,
Abstract:
Demonstration of the histopathological and immunohistochemical effects of a novel hemostatic agent, ankaferd blood stopper, on vascular tissue in a rat aortic bleeding model
Ozer Kandemir, Mustafa Buyukates, Nilufer Kandemir, Erol Aktunc, Aylin Gul, Sanser Gul, S Akin Turan
Journal of Cardiothoracic Surgery , 2010, DOI: 10.1186/1749-8090-5-110
Abstract: Four groups of 11 Wistar albino rats were used. The abdominal aortas of the rats were wounded; an ABS-soaked tampon was applied to rats in Groups 1 and 3, and a plain gauze tampon was applied to rats in Groups 2 and 4 until the bleeding stopped. The bleeding time was recorded. Immediately following sacrificing, the arteriotomy sites from Groups 1 and 2 were removed. The abdominal incisions in Groups 3 and 4 were closed following hemostasis. On Day 7 of the study, Group 3 and 4 rats were sacrificed and the abdominal aorta arteriotomy sites were removed for histopathological and immunohistochemical evaluation.The mean bleeding time in 15 animals in Groups 2 and 4 was 4.9 ± 0.6 s, and in 22 animals in Groups 1 and 3 was 3.1 ± 0.6 s. Distal aortic occlusion was not observed on either Day 1 or 7 in any group. Significantly more widespread and dense endothelial nitric oxide synthase (eNOS) staining was observed in Group 1 animals than Group 2. On Days 1 and 7 after application of ABS, histopathological changes, consisting of necrosis, inflammation, and endothelial cell loss, in the rat abdominal aortas did not differ between Groups 1 and 2. The basophilic discoloration in the ABS group on the operation day was a result of a foreign body reaction and hemosiderin-loaded histiocyte accumulation, which occurred on Day 7.In this study, hemostasis was successfully achieved with ABS in rat abdominal aortas. No histopathological change was found in the rat abdominal aortas between the ABS and control groups on Days 1 and 7. Further studies on the long-term effects of foreign body reactions and hemosiderin-loaded histiocyte accumulation are required.Impaired tissue integrity and uncontrollable hemorrhage are important causes of morbidity and mortality, especially in the presence of coagulopathies [1]. Various hemostatic agents have been developed to achieve sufficient hemostasis [2,3]. In cardiovascular surgery, bleeding from anastomosis sites is usually controlled with pressure o
Effect of heparin in the intraocular irrigating solution on postoperative inflammation in the pediatric cataract surgery
Yelda B Özkurt,Arzu Taskiran,Nadire Erdogan,Baran Kandemir
Clinical Ophthalmology , 2009,
Abstract: Yelda B zkurt, Arzu Taskiran, Nadire Erdogan, Baran Kandemir, mer K Dog?anDepartment of Ophthalmology, Kartal Training and Research Hospital, Istanbul, TurkeyPurpose: To evaluate the influence of irrigation of the anterior chamber with heparin sodium on postoperative inflammation after pediatric cataract surgery. Setting: Kartal Training and Research Hospital, First Eye Clinic, Istanbul, Turkey.Design: Randomized prospective double-blind study.Methods: Fourteen consecutive eyes from 14 patients aged 8.9 ± 5.9 years, (range 3–18 years) (group 1) and 19 eyes from 19 patients aged 9.1 ± 5.2 (range 1.5–18 years) (group 2) underwent pediatric cataract surgery. Five patients in group 1 were between three and five years old. One patient was 1.5 years old and six patients in group 2 were between three and five years old. During the procedure, group 1 received anterior chamber irrigation with heparin sodium (5 IU/cc) and 1 ml of heparin sodium (concentration 10 IU/ml) added to the irrigating balanced salt solution (BSS Plus; Alcon Laboratories, Inc., Fort Worth, TX, USA) while group 2 received BSS without heparin sodium only. Cases aged under three years received anterior vitrectomy in addition to posterior capsulorrhexis. One eye received anterior vitrectomy in group 1 and two eyes received anterior vitrectomy in group 2. Cases with preoperative complications were not included in the study. Early and late postoperative inflammatory complications, including fibrin formation, anterior and posterior synechia, cyclitic and pupillary membrane formation were recorded and compared.Results: Mild anterior chamber reaction was observed in three patients in Group 1, while nine cases in group 2 experienced marked anterior chamber reaction. In four of nine patients from group 2, anterior chamber reaction was severe and resulted in pupillary membrane and synechia despite treatment in the postoperative 7th day, while in all three cases in group 1, reaction disappeared by the 7th day.Conclusion: Anterior chamber irrigation with heparin during pediatric cataract surgery may minimize early inflammatory reaction and decrease the number of postoperative inflammatory related complications.Keywords: pediatric, cataract, surgery, inflammation
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