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Yayın Vapor-induced film formation from low-T-g particles for different solvent compositions(Elsevier Inc, 2006-05-15) Arda, Ertan; Kara, Selim; Saraç, Ayfer; Pekcan, Mehmet ÖnderThe photon transmission method was used to study latex film formation from poly(vinyl acetate) (PVAc) particles induced by two different solvents. Films with the same latex content were prepared from PVAc particles and exposed to vapor of ethanol-water and acetone-water mixtures in various compositions. Transmitted photon intensities, I-tr, from these films increased with increasing vapor exposure time. The increase in I-tr is attributed to the increase in crossing density at the polymer-polymer junction. The Prager-Tirrell model was employed to obtain the back-and-forth frequency, v, of the reptating polymer chain during film formation induced by solvent vapor. It was observed that the produced v values increase as the solvent content is increased for both solvents. Abilities of both solvents to form films were interpreted with the solubility parameters of the solvents and the PVAc.Yayın The boundary layer approximation and nonlinear waves in elastic tubes(Pergamon-Elsevier Science, 2000-09) Antar, Nalan; Demiray, HilmiIn the present work, employing the nonlinear equations of an incompressible, isotropic and elastic thin tube and approximate equations of an incompressible viscous fluid, the propagation of weakly nonlinear waves is examined. In order to include the geometrical and structural dispersion into analysis, the wall's inertial and shear deformation are taken into account in determining the inner pressure-inner cross sectional area relation. Using the reductive perturbation technique, the propagation of weakly nonlinear waves, in the long-wave approximation, are shown to be governed by the Korteweg-de Vries (KdV) and the Korteweg-de Vries-Burgers (KdVB), depending on the balance between the nonlinearity, dispersion and/or dissipation. In the case of small viscosity (or large Reynolds number), the behaviour of viscous fluid is quite close to that ideal fluid and viscous effects are confined to a very thin layer near the boundary. In this case, using the boundary layer approximation we obtain the viscous-Korteweg-de Vries and viscous-Burgers equations.Yayın A factorized high dimensional model representation on the nodes of a finite hyperprismatic regular grid(Elsevier Science inc, 2005-05-25) Tunga, Mehmet Alper; Demiralp, MetinWhen the values of a multivariate function f(x(1),...,x(N)), having N independent variables like x(1),...,x(N) are given at the nodes of a cartesian, product set in the space of the independent variables and ail interpolation problem is defined to find out the analytical structure of this function some difficulties arise in the standard methods due to the multidimensionality of the problem. Here, the main purpose is to partition this multivariate data into low-variate data and to obtain the analytical structure of the multivariate function by using this partitioned data. High dimensional model representation (HDMR) is used for these types of problems. However, if HDMR requires all components, which means 2(N) number of components, to get a desired accuracy then factorized high dimensional model representation (FHDMR) can be used. This method uses the components of HDMR. This representation is needed when the sought multivariate function has a multiplicative nature. In this work we introduce how to utilize FHDMR for these problems and present illustrative examples.Yayın On the existence of some evolution equations in fluid-filled elastic tubes and their progressive wave solutions(Pergamon-Elsevier Science Ltd., 2004-09) Demiray, HilmiIn the present work, by employing the nonlinear equations of motion of an incompressible, isotropic and prestressed thin elastic tube and the approximate equations of an incompressible inviscid fluid, we studied the existence of some possible evolution equations in the longwave approximation and their progressive wave solutions. It is shown that, depending on the set of values of the initial deformation, it might be possible to obtain the conventional Korteweg-deVries (KdV) and the modified KdV equations of various forms. Finally, a set of progressive wave solutions is presented for such evolution equations.Yayın Elucidation of the complete set of H-2 electronic states' vibrational data(Pergamon-Elsevier Science Ltd, 2004-11) Yarman, Nuh TolgaWe have previously established that, the vibration period T of a diatomic molecule, can be expressed as T = [4pi(2)/(rootninjh)]rootgM(0)m(e)r(2), where M-0 is the reduced mass of the nuclei, M-e the mass of the electron, r the internuclear distance of the molecule at the given electronic state, It the Planck Constant, and g a dimensionless and relativistically invariant coefficient, which appears to be a characteristic of the electronic configuration of the molecule. Herein we validate this relationship, chiefly on the basis of vibrational data of H-2 molecule's electronic states, and achieve its calibration, vis-a-vis the quantum numbers that it is to involve. This, basically yields, the elucidation of the complete set of H-2 spectroscopic data. Thus, the composite quantum number n(1)n(2) along our finding is nothing but the ratio of the internuclear distance r at the given electronic state, to the internuclear distance r(0) at the ground state. This makes that for electronic states configured alike, for which g is expected to remain the same, T-2 versus r(3), should exhibit a linear behavior. Our approach can well be applied to other molecules.Yayın Fluorescence study on Al2O3-polystyrene latex composite film formation(John Wiley & Sons Inc, 2005-06) Uğur, Şaziye; Salman, Oğuz Umut; Tepehan, Galip Gültekin; Tepehan, Fatma Zehra; Pekcan, Mehmet ÖnderThis work reports a steady state fluorescence (SSF) technique for studying film formation from mixture of Al2O3 and polystyrene (PS) latex particles. The composite films were prepared from dispersion of pyrene (P)labeled PS particles in Al2O3 solution at room temperature and annealed at elevated temperatures in 10-min time interval above glass transition (T-g) temperature of polystyrene. Nine different composites film were studied in various latex contents. Fluorescence intensities (I-P) from P were measured after each annealing step to monitor the stages of film formation. No variations in I-p were detected for the films prepared with higher than 33 wt% Al2O3 content. However films prepared below 33 wt% Al2O3 content show considerable increase in I-P above the certain onset temperature called minimum film forming temperature, To. Healing temperatures T., were determined from the maxima of I-P. Void closure and interdiffusion stages were modeled and related activation energies were determined and found to be 20 and 97 kJ.mol(-1), respectively.Yayın Localized travelling waves in a prestressed thick elastic tube(Pergamon-Elsevier Science, 2001-10) Demiray, HilmiIn the present work, by using the exact non-linear equations of an incompressible inviscid fluid contained in a prestressed thick elastic tube, the propagation of localized travelling wave solution in such a medium is investigated. Employing the hyperbolic tangent method and considering the long-wave limit, we showed that the lowest-order term in the perturbation expansion gives a solitary wave equivalent to the localized travelling wave solution of the Korteweg-de Vries equation. The progressive wave type of solution is also sought for the second-order terms in the perturbation expansion. The correction terms in the speed of propagation are obtained as part of the solution of perturbation equations.Yayın Annular-ring CMUT arrays for forward-looking IVUS: Transducer characterization and imaging(IEEE, 2006-02) Değertekin, Fahrettin Levent; Güldiken, Rasim Oytun; Karaman, MustafaIn this study, a 64-element, 1.15-mm diameter annular-ring capacitive micromachined ultrasonic transducer (CMUT) array was characterized and used for forward-looking intravascular ultrasound (IVUS) imaging tests. The array was manufactured using low-temperature processes suitable for CMOS electronics integration oil a single chip. The measured radiation pattern of a 43 X 140- mu m(2) array element depicts a 40 degrees view angle for forward-looking imaging around a 15-MHz center frequency in agreement with theoretical models. Pulse-echo measurements show a -10-dB fractional bandwidth of 104% around 17 MHz for wire targets 2.5 mm away from the array in vegetable oil. For imaging and SNR measurements, RF A-scan data sets from various targets were collected using all interconnect scheme forming a 32-element array configuration. An experimental point spread function was obtained and compared with simulated and theoretical array responses, showing good agreement. Therefore, this study demonstrates that annular-ring CMUT arrays fabricated with CMOS-compatible processes are capable of forward-looking IVUS imaging, and the developed modeling tools can be used to design improved IVUS imaging arrays.Yayın Solitary waves in fluid-filled elastic tubes: weakly dispersive case(Pergamon-Elsevier Science, 2001-03) Demiray, HilmiIn the present work, employing the nonlinear equations of an incompressible, isotropic and elastic thin tube and the approximate equations of an incompressible inviscid fluid, the propagation of weakly nonlinear waves, in such a medium is studied through the use of the modified multiple expansion method. It is shown that the evolution of the lowest order (first-order) term in the perturbation expansion may be described by the Korteweg-de Vries (KdV) equation. The governing equation for the second-order terms and the localized travelling wave solution for these equations are also obtained. The applicability of the present model to flow problems in arteries is discussed.Yayın A phase diagram near the NAC point in liquid crystals(Elsevier Science SA, 2002-07-28) Salihoğlu, Selami; Yurtseven, Hamit; Enginer, YücelIn this study using a mean field model we obtain the phase line equations for the NA. NC and AC transitions near the NAC point in a mixture of liquid crystals. We then fit these phase line equations to the experimental data. This fitting shows that our theoretical phase diagram predicts the correct experimental behaviour of the phase diagram in a mixture of liquid crystals.
