Halil Berberoglu

Determination of whey adulteration in milk powder by using laser induced breakdown spectroscopy

A rapid and in situ method has been developed to detect and quantify adulterated milk powder through adding whey powder by using laser induced breakdown spectroscopy (LIBS). The methodology is based on elemental composition differences between milk and whey products. Milk powder, sweet and acid whey powders were produced as standard samples, and milk powder was adulterated with whey powders. Based on LIBS spectra of standard samples and commercial products, species was identified using principle component analysis (PCA) method, and discrimination rate of milk and whey powders was found as 80.5%. Calibration curves were obtained with partial least squares regression (PLS). Correlation coefficient (R(2)) and limit of detection (LOD) values were 0.981 and 1.55% for adulteration with sweet whey powder, and 0.985 and 0.55% for adulteration with acid whey powder, respectively. The results were found to be consistent with the data from inductively coupled plasma - mass spectrometer (ICP-MS) method.

Efficient Numerical Algorithm for Cascaded Raman Fiber Lasers Using a Spectral Method

Over recent decades, fiber Raman lasers (FRLs) have received much attention from researchers and have become a challenge for them both numerically and experimentally. The equations governing the FRLs are in the form of a first-order system of nonlinear two-point boundary-value ordinary differential equations. In this paper, an algorithm for solving this system of differential equations using a spectral method, namely Chebyshev pseudospectral method is presented in detail and then numerical simulations are performed. The main advantage of the spectral methods is in their optimality in achieving high accuracy by using fewer degrees of freedom under suitable conditions. It is shown that the proposed spectral method in combination with the Newton method results in a considerable reduction in the size of the discretized problem and in the computational effort to achieve high accuracy. In this paper, a new approach for constructing an initial approximate solution for the Newton iteration is also presented.

Determination of balance degree of spinning gyro disk by using optical feedback interferometry

We investigate the application of optical feedback interferometry (OFI) for balance adjustments of rotating mechanical gyroscopes that are used in many areas such as aeronautics industry. We compare our results with the industrial balancing machine which measures the amount and position degree of horizontally rotating gyroscope disk. Measurement results show that OFI can be used as an alternative for balance checking. Optical feedback interferometry is based on the mixing of laser light in the cavity with the portion of light which is reflected back to the cavity. Self-mixing interferometric effect occurring in the cavity carries the information about the object movement with high precision such as fluctuations from the ideal value. In this work, we report that OFI offers promising results for measuring unbalance of high precision spinning gyroscopes or rotors used in industry.

Variational Approach to Power Evolution in Cascaded Fiber Raman Laser

A variational approach is formulated and implemented for numerically solving a system of nonlinear two-point boundary value problem (BVP) with coupled boundary conditions modeling the power evolution in cascaded fiber Raman laser with the fiber Bragg gratings at the ends of the cavity. The nonlinearity is treated by successive linearization and the coupled boundary conditions are naturally incorporated into the system through integration in the variational setting. A global approximation of the dependent variables in terms of Legendre polynomials is used to provide a stable Lagrangian interpolation representation as well as the Legendre-Gauss quadrature for accurate numerical evaluation of integrals in the variational formulation. An initial approximate solution is constructed for the delicate convergence to the solution. The approach is validated against an approximate analytic solution and some exact integrals of the variables. The numerical experiments show exponential (spectral) accuracy achieved with much lower resolution in comparison to a widely available BVP solver. Further numerical experiments are performed to reveal the physical characteristics of the underlying model.

Numerical improvement of terahertz time-domain spectroscopic measurements

We have developed an algorithm to efficiently eliminate unwanted reflections typically observed in the data obtained by Terahertz time-domain spectroscopic (THz-TDS) methods. The algorithm works by eliminating the reflections from the boundaries. The numerical improvement of the data allows better analysis of the critical parameters obtained by THz-TDS systems.