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Öğe Characterization of pressure fields of focused transducers at TUBITAK UME(Elsevier Science Bv, 2015) Karaboce, B.; Sahin, A.; Ince, A. T.; Skarlatos, Y.Field radiated by HIFU (High Intensity Focused Ultrasound) has been investigated by measuring its pressure field and mapping in 2-D and 3-D. A new ultrasound pressure measurement system has been designed and constructed at TUBITAK UME (The Scientific and Technological Research Council of Turkey, the National Metrology Institute). System consists of a water tank, positioning system, measurement devices and a controlling program. The hydrophone was attached to a 3-axis, computer-controlled positioning system for alignment with the ultrasound source. The signal was captured and analyzed by the commercially available LabVIEW 8.1 software. The measurements of the ultrasound field were carried out with a needle hydrophone. For each waveform, p, p+ and p- pressures have been calculated. Wave behaviors produced by the KZK model and from experiments look like similar in general. In p, p+, p- the focal point, zero point after the primary peak (focus) and extremum points in the near field well match. (C) 2015 The Authors. Published by Elsevier B.V.Öğe Finite amplitude pressure field of elliptical and rhomboid transducers in three dimensions(Pleiades Publishing Inc, 2011) Kaya, O. A.; Kaleci, D.; Sahin, A.Design of different type of transducers to enhance image quality by forming narrow beams at the principals of nonlinear acoustics is considered in the paper. Thus, the nonlinear pressure fields of elliptical and rhomboid transducers were simulated in three dimensions. The simulation method presented in this study is based on Aanonsen's model for circular sources, and closely follows the model that recently explored for the nonlinear wave propagation due to square and rectangular sources in three dimensions [Kaya et al. Pressure field of rectangular transducers at finite amplitude in three dimensions, Ultrasound in Med. Biol., vol. 32, no. 2, pp. 271-280, 2006]. It is assumed that elliptical and rhomboid sources are plane sources, and driven at 2.25 MHz fundamental frequency. Typical results of nonlinear acoustical pressure field simulation are presented there in three dimensions for elliptical and rhomboid sources and compared with the results for rectangular source. The similarities and differences between the nonlinear pressure field of rectangular, elliptical and rhomboid sources are discussed. The numerical results show that diffraction effects and acoustical beam cross section depend on the source geometry a lot. It is noticeable that the nonlinear pressure field of a rectangular source has a broader beam profile than elliptical and rhomboid source.Öğe Negative refractions by triangular lattice sonic crystals in partial band gaps(Iop Publishing Ltd, 2015) Alagoz, S.; Alagoz, B. B.; Sahin, A.; Nur, S.This study numerically demonstrates the effects of partial band gaps on the negative refraction properties of sonic crystal. The partial band gap appearing at the second band edge leads to the efficient transmissions of scattered wave envelopes in the transverse directions inside triangular lattice sonic crystal, and therefore enhances the refraction property of sonic crystal. Numerical simulation results indicate a diagonal guidance of coupled scattered wave envelopes inside crystal structure at the partial band gap frequencies and then output waves are restored in the vicinity of the output interface of sonic crystal by combining phase coherent scattered waves according to Huygens' principles. This mechanism leads to two operations for wavefront engineering: one is spatial wavefront shifting operation and the other is convex-concave wavefront inversion operation. The effects of this mechanism on the negative refraction and wave focalization are investigated by using the finite difference time domain (FDTD) simulations. This study contributes to a better understanding of negative refraction and wave focusing mechanisms at the band edge frequencies, and shows the applications of the slab corner beam splitting and SC-air multilayer acoustic system.Öğe pH-sensitive chitosan-PEG-decorated hollow mesoporous silica nanoparticles could be an effective treatment for acute myeloid leukemia (AML)(Springer, 2022) Ultav, G.; Tonbul, H.; Tavukcuoglu, E.; Ozturk, S. C.; Akbas, S.; Sahin, A.; Esendagli, G.Improved treatment of acute myeloid leukemia (AML) could be possible by longer retention of anticancer drugs in the bloodstream. In this study, it was aimed to obtain improved treatment against AML by providing prolonged blood levels of doxorubicin and ensuring endosomal escape by the proton sponge effect. With this aim, pH-sensitive and chitosan-poly ethylene glycol (Cs-PEG) coated doxorubicin-loaded hollow mesoporous silica nanoparticles (C-HMSN-DN) were prepared. Nanoparticles (NPs) were characterized by dynamic light scattering (DLS), zeta potential, transmission electron microscopy (TEM), X-Ray diffraction (XRD), and nitrogen adsorption-desorption isotherms. High doxorubicin encapsulation efficacy was obtained as 90%. pH-sensitive formulations were showed higher cellular uptake and found more effective against human leukemia cell line (HL60) than non-pH sensitive formulations. In vivo studies showed that Cs-PEG coating prolonged blood circulation time tremendously in comparison to unmodified nanoparticles and free doxorubicin. The designed drug delivery system (DDS) can be more effective by endosomal escape to eliminate myeloid cells which are granular cells containing a great number of lysosomes. In conclusion, we present a drug delivery system that provides a prolonged blood circulation time due to Cs-PEG coating and effective drug delivery via pH-sensitive drug release and endosomal escape for AML treatment.
