In the first part of the study, power conversion efficiency enhancement of organic solar cells by addition of gold nanorods and gold nanostars into PEDOT: PSS (Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)) layer was investigated. Efficiency of each sample set has been characterized by measuring current density-voltage characteristics. The best efficiencies obtained during this study are 2.88 % and 2.54 % by addition of gold nanostars and nanorods, respectively. The increase in PCEs is notable when these values are compared with the ones (1.67 %) obtained with a reference device which is prepared without adding any gold nanoparticles under the same conditions. In the second part of the study, branched gold nanoparticles were succesfully grown directly on different types of surfaces such as glass, silicon wafer, and indium-tin-oxide (ITO) coated glass with a simple solution-based method in order to utilize them for further applications.

Snores are breath sounds that most people produce during sleep and they are reported to be a risk factor for various sleep disorders, such as obstructive sleep apnea syndrome (OSAS). Diagnosis of sleep disorders relies on the expertise of the clinician that inspects whole night polysomnography recordings. This inspection is time consuming and uncomfortable for the patient. There are surgical and therapeutic treatments. However, evaluation of the success of these methods also relies on subjective criteria and the expertise of the clinician. Thus, there is a strong need for a tool to analyze the snore sounds automatically, and to produce objective criteria and to assess the success of the applied treatment by comparing these criteria obtained before and after the treatment. In this thesis, we proposed a new algorithm to detect snoring episodes from the sleep sound recordings of the individuals, and created a user friendly interface to process snore recordings and to produce simple objective criteria to evaluate the results. The algorithm classifies sleep sound segments as snores and nonsnores according to their subband energy distributions. It was observed that inter- and intra-individual spectral energy distributions of snore sounds show significant similarities. This observation motivated the representation of the feature vectors in a lower dimensional space which was achieved using principal component analysis. Sleep sounds can be efficiently represented and classified as snore or nonsnore in a two dimensional space. The sound recordings were taken from patients that are suspected of OSAS pathology while they were connected to the polysomnography in G&uuml / lhane Military Medical Academy Sleep Studies Laboratory. The episodes taken from 30 subjects (18 simple snorers and 12 OSA patients) with different apnea/hypopnea indices were classified using the proposed algorithm. The system was tested by using the manual annotations of an ENT specialist as a reference. The system produced high detection rates both in simple snorers and OSA patients.

Every year, certain animal and insect species flock together to make long-range migrations to reach their feeding or breeding grounds. A number of interesting observations can be made regarding this phenomenon. First, individuals tend to create large flocks, which can include millions of individuals in fishes, for these migrations. Second, migrations typically cover long distances. Third, despite all kinds of disturbances affecting the individuals during these migrations, the flocks can reach the very same breeding or feeding grounds with remarkable accuracy. Biological studies indicated that these animals mainly use the magnetic field of earth (among many other environmental cues) to determine the direction of their travel. It was also claimed that migrating in flocks has been the key factor behind the accuracy of reaching the same grounds at the end of the migration. In this thesis, we take a constructivist approach towards investigating the effects of flocking in long-range travels using a swarm of physical and simulated mobile robots. Specifically, we extend a self-organized flocking behavior that was developed by Turgut et al. (2008) that allows the long-range migration of a robotic swarm in space using the magnetic field of the earth. Using this behavior, we analyze how the accuracy of the robotic swarm reaching a particular &quot / breeding ground&quot / is affected by four factors / namely, (1) averaging through the heading alignment, (2) noise in sensing the homing direction, (3) differences in the characteristics of the individuals, and (4) disturbances caused by the proximal interactions of the robots during flocking. Through systematic experiments with physical and simulated robots, we analyze how these factors affect the accuracy along with the flock size and different sources of noise.

This thesis reports a detailed characterization of indium arsenide antimonide (InAs1- xSbx) photodetectors grown on gallium arsenide (GaAs) substrate by molecular beam epitaxy. A combination of polyimide and sulphur and a single layer of polyimide were used as passivation films in this study. Two different epilayer structures were used for assessing the detector performance and comparing the above passivation layers. For the first structure, the optical measurements revealed that Sb mole fraction was 0.13 and the cut-off wavelength was around 4.1 &micro / m at 80 K. The Sb mole fraction of the second structure was 0.2, and the 77 K cut-off wavelength was 4.8 &micro / m. Detailed electrical and optical characterizations were performed on 33x33 &micro / m2 test diodes. The photodiodes yielded peak detectivities of ~3.65x1010 and ~1.22x1010 cmHz1/2/W at 80 K for the first and second structures, respectively. Considerable 1/f noise current related with trap-assisted tunneling mechanism was observed in both structures at 80 K. Dark current modeling study showed that the dark current was dominated by the shunt and trap-assisted tunneling mechanisms throughout the entire reverse bias voltages for both detectors. The dark current analysis of variable area detectors fabricated with both epilayer structures revealed that the reverse bias current was mainly generated by the surface leakage in small sized (33x33 &micro / m2) detectors for both passivation layers. However, the surface current contribution was observed to be lower for the double layer (polyimide and sulphur) passivated detectors suggesting that it is a better passivation technique.

In the subject of Computational Fluid Dynamics (CFD), there seems to be small number of important progress in the pressure-based methods for several decades. Recent studies on the implicit coupled algorithms for pressure-based methods have brought a new insight. This method seems to provide a huge reduction in the solution times over segregated methods. Fully implicit coupled algorithm for pressure-based methods is very new subject with only few papers in literature. One of the most important work in this area is referenced as [1] in this thesis. Another source of information about the method comes from a commercially available code FLUENT which includes the algorithm as an option for pressure-based solver. However the algorithm in FLUENT does not seem to be a fully implicit with a little information in its manual. In this thesis, a fully implicit coupled pressure-based solver is developed mainly based on the available literature. The developed code is succesfully tested against some test cases.

The main objective of this study was to investigate micro and nano cacao fibers and their effects on quality, texture and staling of cakes. In the first part of the study, rheological properties of cake batter with different concentrations (0 %, 3 %, 6 %, 9 %, 12 %) cacao micro and nano fiber, and cacao powder were determined. Cake batter was found to show shear thinning and time independent behavior for all formulations and fit the Power Law model. The viscosity increased as the percentage of fiber increased. Both G&rsquo / and G&rsquo / &rsquo / values increased with oscillatory frequency and percentage of fiber. In the second part of the study, physical properties (specific volume, texture, color and weight loss), sensory properties of cakes and textural changes during storage were determined. Addition of micro and nano cacao fibers to the cake formulation decreased specific volume, weight loss and L* values. It increased hardness, springiness, chewiness, resilience and elastic recovery values and minimized textural changes during storage. Fiber addition also improved the cake acceptability of the cakes in terms of odor, taste and color.

Shrimp and mussel samples were cleaned, washed and exposed to steam before freezing. HHP treatment was performed at combinations of 200, 220 and 250 MPa at 25, 30, 40 and 50&deg / C for 10 and 20 minutes. Microbial analysis were performed by analyzing the effect of treatments on the microbial reduction in the samples. Based on the results of the microbial reduction, the best combinations of HHP treatments were determined as 250 MPa, 50&deg / C, 10 minute for shrimps and 220 MPa, 50&deg / C, 10 minute for mussels where total microbial inactivation was achieved. Storage analysis was performed on the samples, treated at the selected HHP combinations and stored at room (25&deg / C) and refrigeration temperatures (4&deg / C). For the storage analysis, variations in Total Volatile Bases (TVB-N) and pH were measured. According to the results evaluated, shelf-life of the shrimps were detected as 10 and 16 days for storage at room and refrigeration temperature, respectively as compared to 4 days of untreated sample at 4oC. Similarly shelf-life for the mussel samples were obtained as 12 days for storage at room and 18 day for storage at refrigeration temperature as compared to 4 days of untreated sample at 4oC. HHP-at the studied parameters for shrimps and mussels- can be offered as an alternative method for the preservation of shell-fish instead of conventional frozen food technology, which is currently used in the industry, since it gives the opportunity to handle the samples at lower temperatures for the post-production period resulting in both reduction of energy required and operational costs without sacrificing from the quality as measured by microbial reduction, TVB-N and pH.

Space-based infrared Earth observation systems provide a unique opportunity for the detection of thermal variations on Earth&amp / #8217 / s surface or atmosphere. The objective of this study is to propose an optical design of a thermal imager that is suitable for flight on a micro-satellite platform at an altitude of 650 km, providing the necessary resolution requirements under the considerations of physical boundaries of the given platform. Before the optical design, the parameters which would strictly bound the optical system such as the infrared source, atmospheric transmission, the detector and optical materials for infrared as well as the working conditions for the microsatellite were examined. Simulations and further optimization efforts resulted with a high performance optical system design.

Drying is a process of moisture removal due to simultaneous heat and mass transfer. High hydrostatic pressure (HHP) processing subjects liquid and solid foods, with or without packaging, to pressures between 100 and 800 MPa. The application of HHP affects cell wall structures, leaving the cells more permeable, facilitating the diffusion and providing higher drying rates. In this study, two variety of apples, i.e. Amasya and red delicious, green beans and carrots were pretreated with HHP at different pressure-time-temperature combinations (100 &ndash / 300 MPa for 5 &ndash / 45 min at 20 and 35&deg / C) prior to drying. Hot air drying experiments were carried at different temperatures (27, 45, 65, and 85&deg / C) and air velocity of 0.4 and 0.8 m/s. To obtain the drying data, samples were subjected to hot air drying under constant external conditions. The applicability of 14 kinetic models selected from the literature for the drying of fruits and vegetables was determined by appropriate statistical analyses procedures. Improving the drying conditions by increasing the drying temperature generally masked the effect of HHP pretreatment on drying rate. Only for green beans, HHP treatments at 20&deg / C decreased the drying rate. Generally pressures of HHP pretreatment higher than 100 MPa caused cell permeabilization resulted in higher drying rates for apples and carrots. Among the 14 models, modified Page model for apples, and modified Page and two term exponential models for green beans and carrots were found to best explain the drying behaviors.

In this thesis, the effect of registration process is evaluated as well as several methods proposed for 3D face recognition. Input faces are in point cloud form and have noises due to the nature of scanner technologies. These inputs are noise filtered and smoothed before registration step. In order to register the faces an average face model is obtained from all the images in the database. All the faces are registered to the average model and stored to the database. Registration is performed by using a rigid registration technique called ICP (Iterative Closest Point), probably the most popular technique for registering two 3D shapes. Furthermore some variants of ICP are implemented and they are evaluated in terms of accuracy, time and number of iterations needed for convergence. At the recognition step, several recognition methods, namely Eigenface, Fisherface, NMF (Nonnegative Matrix Factorization) and ICA (Independent Component Analysis) are tested on registered and non-registered faces and the performances are evaluated.