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Öğe Acceptor 1s-2p± transitions in GaAs/Ga0.7Al0.3As quantum wells(Wiley-V C H Verlag Gmbh, 1998) Akbas, H; Aktas, S; Okan, SE; Ulas, M; Tomak, MThe valence subband energies in the presence of an electric-field are calculated using the fourth-order Runge-Kutta method. The 1s- and 2p(+/-)-like acceptor states in the presence of a magnetic field are then calculated variationally. The effects of the spatially dependent screening function epsilon(r) on the calculation of the transition energies are specifically investigated. The use of a constant epsilon(o) is shown to yield better agreement with experimental results.Öğe Atypical tuberculosis of the spine(Yonsei Univ College Medicine, 2000) Yalniz, E; Pekindil, G; Aktas, SSpinal tuberculosis characteristically involves the paradiscal area of vertebral bodies with a narrowing of che disc space. In this study, we reported four atypical forms of Pott's disease, including one hundred and eighty-four patients treated between 1985 and 1998. Two cases presented with noncontiguous multilevel involvement, where one case had transverse process involvement alone and the other had involvement of the neural arch. Atypical tuberculosis of the spine was found in 2.1% of the patients.Öğe Binding energies of helium-like impurities in parabolic quantum wells under an applied electric field(Academic Press Ltd, 2000) Okan, SE; Akbas, H; Aktas, S; Tomak, MWe present a variational method to compute the binding energies of helium-like impurities in finite parabolic GaAs-Ga1-xAlxAs quantum wells. The effects of band nonparabolicity in the conduction band are taken into account within the effective mass approximation. The dependence of the impurity binding energy on the applied electric field and the impurity position is also discussed together with the polarization effect for all cases. (C) 2000 Academic Press.Öğe Clinical evaluation of ulnar nerve repair at wrist level(Springer-Verlag, 2004) Gurbuz, H; Aktas, S; Calpur, OUIntroduction. In this study, the results of ulnar nerve repair were analyzed. The relation between the functional outcome scores and clinical findings were investigated to find out whether any clinical finding could be predictive of the outcome. Materials and methods. Seventeen patients who underwent ulnar nerve repair formed the study group. Average follow-up lasted 45.5 months (range 39-48 months), and average age of the study group was 31.7 years (range 26-42 years). The same operative technique was applied to all patients by one of the authors (HG). Follow-up checks were done at 3, 6, and 12 months postoperatively. The patients who did not attend the last follow-up were excluded from the study group. The Seddon classification was used as the functional scoring system. Wound healing, Tinel sign, interosseous atrophy, atrophy of the first web space, clawing, and protective sensation were the clinical findings examined at the follow-ups. Wound healing was classified as either normal scar formation or hypertrophic scar-keloid (HsC) formation. Results. Good results in 4 and fair results in 13 were obtained according to the Seddon classification. Statistically, there was no difference between the clinical findings at the 3, 6, and 12 month follow-ups. Conclusion. Presence of HsC and clawing can be regarded as a predictive sign for fair results in nerve repairs.Öğe Donor binding energies in GaAs quantum wells considering the band nonparabolicity effects and the wavefunction elongation(Academic Press Ltd, 2000) Aktas, S; Okan, SE; Erdogan, I; Akbas, H; Tomak, MThe donor binding energies in finite GaAs/GaxAl1-As-x quantum wells have been calculated by considering the confinement of electrons, which increases as the well width increases. The variational solutions have been improved by using a two-parameter trial wavefunction, and by including the conduction band nonparabolicity. It is shown that the method used gives results in agreement with those obtained in the experiments on the effective mass and the donor binding energy, both of which are strongly dependent on the well width. (C) 2000 Academic Press.Öğe Early mobilization after sliding and Z-lengthening of heel cord: a preliminary experimental study in rabbits(Springer-Verlag, 2001) Aktas, S; Ercan, S; Candan, L; Moralar, U; Akata, ESliding lengthening and Z-lengthening techniques are widely used in heel cord lengthening. Even though most surgeons performing these procedures apply a short leg cast after surgery, their postoperative immobilization intervals vary from 3 to 7 weeks. Nather et al. showed that there was no need for immobilization after the musculotendinous lengthening of long, deep flexor tendons. In the present study, we aimed to show the healing process of heel cords lengthened by sliding and Z-plasty lengthening in rabbits that did not undergo any post operative immobilization. We performed sliding lengthening in the right heel cords of the rabbits and Z-lengthening in the left heel cords. We compared these two techniques radiographically, biomechanically, and histopathologically. Even though the biomechanical study showed superior results in the sliding lengthening group on the 7th day, elongation of the tendons at both sites was seen radiographically. There was no statistically significant difference between the sites according to the biomechanical study done on the 28th day. We concluded that the ankle should be immobilized in the early healing phase and that both types of lengthening gain a similar level of strength by the 4th week.Öğe Electric and magnetic field effects on the binding energy of a hydrogenic donor impurity in a coaxial quantum well wire(Elsevier Science Bv, 2005) Aktas, S; Boz, FK; Dalgic, SSThe effect of both an electric and magnetic field on the hydrogenic binding energy of a shallow donor impurity in a coaxial GaAs-(Ga, Al)As quantum well wire (QWW) has been investigated as a function of the impurity position and barrier thicknesses for different values of the applied magnetic and electric field strengths. Within the effective mass approximation, the ground-state energy in the presence of a uniform magnetic field applied parallel to the wire axis has been calculated using the fourth-order Runge-Kutta method. The ground state binding energy under applied electric field has been studied with a variational approach. The two sharp increase in the binding energy have observed for the donor impurity located at outside of the center under the critical electric and magnetic field values. However, for the electric field off the binding energy monotonously decrease with increasing magnetic field strength up to a critical magnetic field and then a sharp decrease is seen before reaching a constant value. For the impurity located at the center, the abrupt deviations of the binding energy strongly depend not only on the electronic confinement, but also on the electric and magnetic field strength. We expect that these results will be useful in technological applications. (c) 2005 Elsevier B.V. All rights reserved.Öğe Electric field effect on the binding energy of a hydrogenic impurity in coaxial GaAs/AlxGa1-xAs quantum well-wires(Academic Press Ltd Elsevier Science Ltd, 2001) Aktas, S; Okan, SE; Akbas, HThe ground state binding energy of a hydrogenic impurity in a coaxial cylindirical quantum well wire system subjected to an external electric field applied perpendicular to the symmetry axis of the wire system is studied within a variational scheme. Binding energy calculations were performed as functions of the inner barrier thickness and the electric field for two different impurity positions. The main result is that a sharp decrease in the binding energy, which may be important in device applications, occurs in certain conditions. (C) 2001 Academic Press.Öğe Evaluation of rotational gait abnormality in the patients cerebral palsy(Lippincott Williams & Wilkins, 2000) Aktas, S; Aiona, MD; Orendurff, MInternal rotation of hip is commonly seen in children with cerebral palsy. Existing muscle imbalance causes persistence of femoral deformity, which may contribute to rotational asymmetry. In cerebral palsy, gait deviations are the result of dynamic and static components, both caused by muscle imbalance. In this study we investigated the predict ability of hip rotation in gait from the measurement of anatomic deformity. Computed tomography (CT) measurements of femoral anteversion and physical examination data failed to predict the hip rotation in gait. However, tibial (CT) measurements and physical examination data highly correlated with tibial rotation in gait. We conclude the dynamic component of hip rotation during gait is significant, as anatomic deformity did not predict gait deviations.Öğe The exciton transition energies in symmetric double GaAs/AlxGa1-xAs quantum wells(Wiley-V C H Verlag Gmbh, 1999) Okan, SE; Aktas, S; Akbas, H; Tomak, MThe exciton transition energies between valence and conduction subbands of symmetric double quantum wells are studied. To study the effect of geometry coupled wells of rectangular, graded and parabolic shapes are considered. A special emphasis is given to the study of crossover between the symmetric light-hole (e1-11) and the antisymmetric heavy-hole (e2-h2) transitions.Öğe Magnetic field effect on the binding energy of a hydrogenic impurity in coaxial GaAs/AlxGa1-xAs quantum well wires(Academic Press Ltd- Elsevier Science Ltd, 2005) Boz, FK; Aktas, SWe propose a coaxial cylindrical quantum well wire (QWW) system, in which two conducting cylindrical layers are separated by an insulating layer. The ground state binding energy of a hydrogenic impurity subjected to uniform magnetic field applied parallel to the wire axis is studied within a variational scheme as a function of the inner barrier thickness for two different impurity positions and various barrier potentials. The ground state energy and wave function in the presence of a magnetic field is directly calculated using the fourth-order Runge-Kutta method. It is found that the binding energy in critical barrier thickness shows a sharp increase or decrease depending on the impurity position and magnetic field strength. The main result is that a sharp variation in the binding energy, which may be important in device applications, depends strongly not only on the location of the impurity but also on the magnetic field and the geometry of the wire.Öğe Magnetic resonance imaging in follow-up of treated clubfoot during childhood(Elsevier Sci Ireland Ltd, 2001) Pekindil, G; Aktas, S; Saridogan, K; Pekindil, YIn this study, we evaluated the short-term results of surgically treated clubfoot with magnetic resonance imaging (MRI). T1- and T2-weighted MRI images with 4-mm slices in the standard anatomic sagittal, transverse, and coronal planes were obtained in seven cases of clubfoot aged 4-11 years (mean 5.6 years old). The mean follow-up period was 3.6 years (ranged between 2 and 6 years). Sagittal talocalcaneal angle, talar head and neck axis internal rotation, calcaneal axis internal rotation, transverse talar neck and head/calcaneus angle and posterior calcaneus external rotation were measured. Three cases with dorsal talonavicular subluxation and a case of calcaneocuboid luxation were demonstrated by MRI. It was concluded that MRI may help to understand results of surgically-treated clubfoot by revealing hindfoot articular relationships and many complications. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.Öğe Patellar metastasis from a lung epidermoid carcinoma(Yonsei Univ College Medicine, 1998) Aktas, S; Demiral, H; Bilgi, S; Caglar, T; Calpur, OUPatellar metastases are very rare. There have been approximately 20 cases reported in the literature. We have also noted two Other reports of patellar metastasis from lung carcinoma as the first manifestation of lung cancer in our literature review. We present a case of patellar metastasis; as the first manifestation of lung epidermoid carcinoma in a patient who was a smoker for 33 years.Öğe Patterns of single segment non-physeal extremity fractures in children(Springer Verlag, 1999) Aktas, S; Saridogan, K; Moralar, U; Ture, MFive hundred and fifteen children with single segment non-physeal extremity fractures were retrospectively reviewed, The male to female ratio was 2.7:1. The average age of study group was 9.9+/-4.7 years; 273 fractures (53 %) were on the left, 242 (47 %) were on the right. A fall was the main cause of the injury in most of the cases (80%). The forearm was the most commonly seen fracture site. Summer was the season when the fracture incidence was the highest. Highest surgical treatment rate (50%) was seen in supracondylar humerus fractures. It has been stated in the literature that non-physeal fractures are far more common than physeal fractures, We assume that this study not only will help understanding of the injury patterns of single segment :non-physeal fractures in children but also, be a base for future studies in prevention and treatment of this type of fracture.Öğe The radiological analysis of pes cavus deformity in Charcot Marie Tooth disease(Lippincott Williams & Wilkins, 2000) Aktas, S; Sussman, MDCharcot Maric Tooth (CMT) is a progressive hereditary peripheral neuropathy. The most prevalent subtype is CMT-1A, wherein patients develop a characteristic cavovarus deformity. We have reviewed a series of standing lateral foot radiographs of patients with foot deformity due to CMT, and found that the hind foot of these patients is in dorsiflexion, not equinus, and that the apparent equinus is due to plantar flexion of the forefoot on the midfoot, and actually represents a cavus deformity.Öğe Screening effect on the binding energies of shallow donors, acceptors and excitons in finite-barrier quantum wells(Academic Press Ltd, 1998) Akbas, H; Aktas, S; Okan, SE; Ulas, M; Tomak, MThe conduction and valence subband energies in the presence of an electric field are calculated using the fifth-order Runge-Kutta method. The binding energies of shallow donors, accepters and excitons in finite-barrier GaAs/Ga1-xAlx As quantum wells are then obtained variationally in the presence of a magnetic field. The effects of a spatially dependent screening function epsilon(r) On the calculation of binding energies are specifically investigated. The use of epsilon(r) in comparison with the use of a constant epsilon(0) increases the binding energy of accepters as the increase on shallow donors and excitons is quite small. (C) 1998 Academic Press Limited.
