Akademik Çıktılar

Permanent URI for this communityhttps://hdl.handle.net/20.500.12416/8602

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A Homotopy Perturbation Solution for Solving Highly Nonlinear Fluid Flow Problem Arising in Mechanical Engineering
(Amer inst Physics, 2018) Khan, Yasir; Baleanu, Dumitru; Akgul, Ali; Faraz, Naeem; Inc, Mustafa; Akgul, Esra Karatas; Baleanu, Dumitru; 56389
In this paper, a highly nonlinear equations are treated analytically via homotopy perturbation method for fluid mechanics problem. The non-linear differential equations are transformed to a coupled non-linear ordinary, differential equations via similarity transformations. Graphical results are presented and discussed for various physical parameters.
A Literature Survey on Integration of Wind Energy and Formal Structure of Buildings at Urban Scale
(Springer international Publishing Ag, 2018) Paltun, Serpil; Gultekin, Arzuhan Burcu; Celebi, Gulser; 2919
Providing the needed and indispensable steady, quality and safe energy is one of the most important issues today. Wind energy is one of the most important renewable energy source. Wind energy has found uses much more in water pumping and obtaining electricity in rural areas until last years. Today, wind energy has taken its place in the energy sector as an alternative source of energy production. High-density building arrays within a city, the combination of indoor and outdoor spaces with different purposes effect wind flow and acceptable wind comfort. In urban areas, wind energy and wind comfort are important requirements. Not only in new urbanisation areas but also for existing urban areas and city centers acceptable wind comfort plays an important role among and around buildings. When viewed from this angle, the aim of this study is enlightening the building aerodynamics, wind effect and wind energy in urban environment, and also giving information about how to analyze the wind comfort and design criteria in dense urban areas.
A new method for dissipative dynamic operator with transmission conditions
(Springer Basel Ag, 2018) Uğurlu, Ekin; Ugurlu, Ekin; Tas, Kenan; Taş, Kenan; 238990; 4971
In this paper, we investigate the spectral properties of a boundary value transmission problem generated by a dynamic equation on the union of two time scales. For such an analysis we assign a suitable dynamic operator which is in limit-circle case at infinity. We also show that this operator is a simple maximal dissipative operator. Constructing the inverse operator we obtain some information about the spectrum of the dissipative operator. Moreover, using the Cayley transform of the dissipative operator we pass to the contractive operator which is of the class With the aid of the minimal function we obtain more information on the dissipative operator. Finally, we investigate other properties of the contraction such that multiplicity of the contraction, unitary colligation with basic operator and CMV matrix representation associated with the contraction.
Beams with arbitrary field profiles in turbulence - art. no. 652209
(Spie-int Soc Optical Engineering, 2006) Baykal, Yahya; 7812
Characteristics of optical beam incidences that have arbitrary field profiles are examined when they propagate in the turbulent atmosphere. Arbitrary source field profile is introduced by decomposing the source into incremental areas and the received field in the presence of turbulence is expressed as the summation of the fields originating from each incremental area. Intensity moments such as average intensity and the scintillation index in turbulence are formulated under such excitation. Our results correctly reduce to the well established Gaussian beam wave solutions when the arbitrary source beam is taken as the Gaussian field profile. Naturally, all the beam structures such as the higher-order single-mode, multimode, off-axis Hermite-Gaussian, Hermite-sinusoidal-Gaussian, higher-order annular, flat-topped-Gaussian beams form the special cases of our derivation. Numerical results that cover the scintillations in turbulence for various types of arbitrary beam profiles are presented. Our results for the arbitrary source field profiles can be applied in atmospheric optics telecommunication links where combination of several known beams are employed as incidence in an effort to reduce the degrading effects of turbulence. Also in the problems of reflection from rough surfaces, propagation of spatially partially coherent optical beams or double passage imaging in turbulence, our formulation can be utilized.
Cavitation in Hydraulic Turbines
(Edizioni Ets, 2019) Ayli, Ece; 265836
Hydroenergy is one of the richest and most useful renewable energy sources in the world. Hydropower is a vital source as it is the clean energy source, sustainable and last but not least it is also cost-effective. One of the most important parameters that affect the performance of the hydraulic machines is the cavitation phenomenon, which is defined as the formation of the vapor bubbles in the liquid through any hydraulic turbine. In this paper, hydraulic machines, cavitation, types of cavitation are briefly described. After theoretical studies, analytical and numerical researches about cavitation in hydraulic machinery are discussed extensively. With those studies which are summarized in this paper covers a lot of ground about cavitation on the other hand further studies are needed about cavitation in hydro turbines. Numerical methods provide sufficient predictions for cavitation. However, numerical results should be verified by experimental measurements and detection methods to decide what intensity and which shape of cavitation is hazardous and vital, where the local pressure is lower than the vapor pressure and at which static pressure cavities start to grow and collapse.
Classification of Linked Data Sources Using Semantic Scoring
(Ieice-inst Electronics information Communication Engineers, 2018) Yumusak, Semih; Doğdu, Erdoğan; Dogdu, Erdogan; Kodaz, Halife; 142876
Linked data sets are created using semantic Web technologies and they are usually big and the number of such datasets is growing. The query execution is therefore costly, and knowing the content of data in such datasets should help in targeted querying. Our aim in this paper is to classify linked data sets by their knowledge content. Earlier projects such as LOD Cloud, LODStats, and SPARQLES analyze linked data sources in terms of content, availability and infrastructure. In these projects, linked data sets are classified and tagged principally using VoID vocabulary and analyzed according to their content, availability and infrastructure. Although all linked data sources listed in these projects appear to be classified or tagged, there are a limited number of studies on automated tagging and classification of newly arriving linked data sets. Here, we focus on automated classification of linked data sets using semantic scoring methods. We have collected the SPARQL endpoints of 1,328 unique linked datasets from Datahub, LOD Cloud, LODStats, SPARQLES, and SpEnD projects. We have then queried textual descriptions of resources in these data sets using their rdfs: comment and rdfs: label property values. We analyzed these texts in a similar manner with document analysis techniques by assuming every SPARQL endpoint as a separate document. In this regard, we have used WordNet semantic relations library combined with an adapted term frequency-inverted document frequency (tfidf) analysis on the words and their semantic neighbours. In WordNet database, we have extracted information about comment/label objects in linked data sources by using hypernym, hyponym, homonym, meronym, region, topic and usage semantic relations. We obtained some significant results on hypernym and topic semantic relations; we can find words that identify data sets and this can be used in automatic classification and tagging of linked data sources. By using these words, we experimented different classifiers with different scoring methods, which results in better classification accuracy results.
Cosine-Gaussian laser beam intensity in turbulent atmosphere
(Spie-int Soc Optical Engineering, 2004) Eyyuboglu, HT; Baykal, Y; 7688
The effects of turbulent atmosphere on cosine-Gaussian laser beams are examined. To this end, a cosine-Gaussian excitation is taken at the source plane, and subsequently the average intensity profile at the receiver plane is formulated. Our formulation correctly reduces to the known Gaussian beam wave result in turbulence and the cosine-Gaussian beam solution in free space (in the absence of turbulence). Variation of the average intensity profile of the receiver plane is evaluated and plotted against the variations of link length, turbulence levels, two frequently used free space optics (FSO) wavelenaths and beam displacement parameters. From these results, it is seen that cosine-Gaussian beam, following the natural diffraction, is eventually transformed into a hyperbolic-cosine Gaussian beam. Hence, the beam energy becomes concentrated around two main lobes at the receiver plane. Combining our earlier result with the findings of this paper, we conclude that cosine-Gaussian and hyperbolic-cosine-Gaussian beam act in a reciprocal manner after having C, propagated. This rneans, starting with a cosine-Gaussian beam excitation, we obtain hyperbolic-cosine-Gaussian distribution at the receiver plane, whereas hyperbolic-cosine-Gaussian beam excitation will yield a cosine-Gaussian distribution. This reciprocity is applicable both in free space and in turbulence.
Damping constant and the inverse relaxation time calculated as a function of pressure using the X-ray diffraction data close to the cubic-tetragonal phase transition in SrTiO3
(Taylor & Francis Ltd, 2019) Yurtseven, H.; Kiracı, Ali; Kiraci, A.; 42475
The damping constant is calculated as a function of pressure at room temperature using the normalized intensity as an order parameter near the cubic-tetragonal phase transition in SrTiO3. The observed X-ray diffraction data are used for the normalized intensities to calculate the damping constant () from the pseudospin-phonon (PS) coupled model and the energy fluctuation (EF) model, which is fitted to the observed FWHM data from the literature for comparison. Using the calculated values, the pressure dependence of the inverse relaxation time () is predicted close to the cubic-tetragonal phase transition in SrTiO3. Our calculated damping constant from both models explains the observed FWHM satisfactorily and our prediction of the inverse relaxation time can also be compared with the experimental measurements when they are available in the literature.
Effects of laser multimode content on the angle-of-arrival fluctuations in free space optics access systems
(Spie-int Soc Optical Engineering, 2004) Eyyuboglu, HT; Baykal, Y; 7688; 7812
The effects of the multimode content in a laser beam on the angle-of-arrival fluctuations are examined for free space optics (FSO) access systems. Multimode excitation is represented by coherent addition of Hermite-Gaussian higher order modes. Root mean square angle-of-arrival fluctuations are formulated using the previously reported multimode phase structure function, which is valid in weak atmospheric turbulence. Results are found for practical FSO links operating at 1550 nm and 850 nm wavelengths and for link spans of up to 5 km. In choosing the mode content, various sequential grouping of all possible mode combinations are used up to a certain order (n,m) mode. We start with the single fundamental mode (TEM00) and span up to the highest order (n = 10, m = 10) mode. In this manner, different degrees of source coherence are also taken into account. Angle-of-arrival fluctuations are found to be in the range of several tens of muradians and almost insensitive to the mode content except for the cases when the mode group terminates with an odd mode. In such instances, the fluctuations rise to a few hundreds of murad. Comparing our results with the field of view of a practical FSO receiver, which is several mrad, we conclude that the-angle-of arrival fluctuations due to multimode excitation will not influence the FSO link performance to a major extent.
Intensity fluctuations for source arrays in turbulent atmosphere - art. no. 630308
(Spie-int Soc Optical Engineering, 2006) Baykal, Yahya; 7812
Intensity fluctuations are formulated for source arrays in weakly turbulent horizontal atmospheric links. Source array is composed of point sources separated by variable distances in the transverse source directions. Formula yielding the on-axis scintillation index for the source array is derived by employing the Rytov solution for the structure and correlation functions in the extended Huygens Fresnel principle. Through numerical results, variations of the scintillations versus the array parameters such as the size of the array, spacing between the array elements, amplitudes and phases of the individual sources in the array are investigated. Numerically evaluated intensity fluctuations for such array parameters are compared with the well known single point source scintillations. We are interested to understand whether the use of a source array will give favorable intensity fluctuations in atmospheric communication links.
Intensity fluctuations of focused general-type beams in atmospheric optics links
(Spie-int Soc Optical Engineering, 2007) Baykal, Yahya; Eyyuboglu, Halil T.; 7812; 7688
The intensity fluctuations of focused general-type beams in weakly turbulent atmospheric links are formulated and numerically evaluated. Focused general-type beams in general cover very large range of beams, however in this work we concentrate specifically on the focused sinusoidal-Gaussian, annular and flat-topped beams. The behavior of the scintillations for these beams is examined versus the focusing distance, wavelength of operation and the source size. In our formulation, atmospheric turbulence is introduced through the Rytov method where the free space field (i.e., in the absence of turbulence) at the receiver plane for the general-type focused beam is found by utilizing the Huygens-Fresnel principle. Figures are presented showing the scintillation index for focused general-type beams and collimated general-type beams. To find out the source and medium parameters that will yield favourable scintillation levels, the intensity fluctuations of the focused sinusoidal-Gaussian, annular and flat-topped beams are compared. Within the range of selected source and medium parameters, our observations indicate that the intensity fluctuations in weak turbulence tend to be the smallest for the focused flat-topped Gaussian beams and the largest for the focused cos-Gaussian beams. Gaussian, cosh-Gaussian and annular beams experience interim level fluctuations. The comparison of the scintillation levels for the mentioned types of focused beams follow the same tendency for all the propagation distances. Also, the intensity fluctuations of the focused general-type beams in turbulence are compared with their collimated counterparts. Such a comparison reveals that for all the beams at a selected source size, the scintillations are nearly the same for both the focused and the collimated cases at all the propagation distances, except for the flat-topped Gaussian beams. When focused flat-topped Gaussian beams are employed, the intensity fluctuations seem to be lower as compared to the equivalent collimated flat-topped Gaussian beam at shorter link lengths.
Internet Gaming Disorder and Treatment Approaches: A Systematic Review
(Turkish Green Crescent Soc, 2018) Nazligul, Merve Denizci; Bas, Samet; Akyuz, Zeynep; Yorulmaz, Orcun
The purpose of this systematic review is to investigate the phenomenology of the psychiatric diagnosis of Internet Gaming Disorder (IGD), which has a serious potential, through the physical and psychosocial impacts of recent candidates for its diagnosis, followed by current treatment approaches for this problem. Using specific terms, a comprehensive database search of PsychINFO, ScienceDirect, Wiley Online Library, Web of Science, and PubMed was conducted to access particular studies that examine treatment interventions for IGD. All searches have been limited to full text papers published between 2000 and 2017. Six eligible treatment studies fulfilling the criteria of preferred reporting items for systematic reviews and meta-analyses (PRISMA) as an international guideline were included in the literature review. The evaluation criteria of the IGD were observed to differ among studies and the current samples to consist predominantly of males in adolescence to young adulthood. The findings on interventions indicate that different treatment modalities show successful results in reducing IGD symptoms and the time spent playing games, as well as on addictive individuals' progress regarding verbal expression. The general impressions of this systematic review are that although technology seems to facilitate life, Internet use and gaming habits at the same time can easily turn into a serious psychiatric problem. On the other hand, relatively little is known about IGD with a rather limited number of studies describing, assessing, and treating this problem. However, increasing information about this disorder is crucial for developing specific interventions. Thus, conducting additional research in Turkey as well as the world is essential for understanding IGD's nature and how to treat it.
Invariant Investigation on the System of Hirota-Satsuma Coupled KdV Equation
(Amer inst Physics, 2018) Hashemi, M. S.; Baleanu, Dumitru; Balmeh, Z.; Akgul, A.; Akgul, E. K.; Baleanu, D.; 56389
We show how invariant subspace method can be extended to the system time fractional differential equations and construct their exact solutions. Effectiveness of the method has been illustrated by the time fractional Hirota-Satsuma Coupled KdV(HSCKdV) equation.
Investigating the Relationship Between SLOC and Logical Database Measures to Improve the Early Estimation of Software Cost
(World Scientific Publ Co Pte Ltd, 2019) Tokdemir, Gul; Tokdemir, Gül; Cagiltay, Nergiz Ercil; 17411
Project planning is a critical activity in the software development life cycle. At the early stages of a project, the managers need to estimate required time, effort and cost to plan, track and then to deliver the project successfully. Many studies have attempted to provide methods for precise software cost estimation. The current software cost estimation methods are mainly based on software size estimation and functional system requirements. The main assumption of this study is that, as the primary source of complexity in today's software is the interaction between the database and the user, database measures may provide inputs allowing current software estimation methods to achieve more accurate results. Accordingly, this study attempts to gain insights from objective measures, collected through the logical database model of software systems, for better prediction of the software's effort and hence cost through software lines of code (SLOC) measure. For this purpose, more than 2.5 million lines of code developed by four different companies, for 79 different software packages with their related database design measures, are analyzed. The results of this study show that there is a close correlation between the software size and database design measure, namely, the number of tables which can be collected at the logical database design stage. By adapting this result, the current estimation models could be improved significantly.
Investigition on the Influence of Parameter Uncertainties in the Position Tracking of Robot Manipulators
(Univ North, 2019) Ghanbarpour Asl, Habib; Han, Kerim Youde
This paper presents a novel trajectory tracking method for robot arms with uncertainties in parameters. The new controller applies the robust output feedback linearization method and is designed so that it is robust to the variation of parameters. Robustness of the algorithm is evaluated when the parameters of the system are floating over 10 percent up and down. An Unscented Kalman Filter (UKF) is applied for state and parameter estimation purposes. As the considered system has 8 unknown parameters while only 5 of them are independent parameters, UKF is applied only to the augmented system with independent parameters. Three types of simulations are applied depending on sensor groups - first with both position and joint sensors, second with only position sensors and third with only joint sensors. The observation of parameters in these groups is discussed. Simulation results show that when both position sensors and joint sensors are used, all the parameters and states are observable and good tracking performances are obtained. When only position sensors are used, the accuracy of the estimated parameters is reduced, and low tracking performances are revealed. Finally, when only joint sensors are applied, the lengths of robot arms are unobservable, but other parameters related to the dynamic system are observable, and poor tracking performances are given.
On the non-commutative neutrix product of the distributions x(+)(lambda) and x(+)(mu)
(Springer Heidelberg, 2006) Fisher, B.; Taş, Kenan; Tas, K.; 4971
Let f and g be distributions and let g(n) = (g * delta(n))(x), where delta(n)(x) is a certain sequence converging to the Dirac delta function. The non-commutative neutrix product f circle g of f and g is defined to be the limit of the sequence {fg(n)}, provided its limit h exists in the sense that [GRAPHICS] for all functions p in D. It is proved that (x(+)(lambda)ln(p)x(+)) circle (x(+)(mu)ln(q)x(+)) = x(+)(lambda+mu)ln(p+q)x(+), (x(-)(lambda)ln(p)x(-)) circle (x(-)mu ln(q)x(-)) = x(-)(lambda+mu)ln(p+q)x(-), for lambda + mu < -1; lambda,mu,lambda+mu not equal -1,-2,... and p,q = 0,1,2.....
Order-disorder transition in the ferroelectric LiTaO3
(Taylor & Francis Ltd, 2019) Kiraci, Ali; Kiracı, Ali; Yurtseven, Hamit; 42475
The temperature dependences of the damping constant and the relaxation time are calculated by using the Raman frequencies of a* and the lowest A(1) (TO) phonons in the ferroelectric phase close to the ferroelectric-paraelectric transition in LiTaO3 (T-C = 963 K). Both calculations are performed by considering the frequency as an order parameter for the pseudospin-phonon (PS) and the energy fluctuation (EF) models using the observed data from the literature. Values of the activation energies of this crystal are also deduced by using both models in this crystal. Our results show that the PS and EF models can describe the observed behavior adequately for the order-disorder transition in LiTaO3.
Propagation of cross beams through atmospheric turbulence
(Spie-int Soc Optical Engineering, 2005) Yenice, YE; Eyyuboglu, HT; Baykal, Y; 7688; 7812
Propagation properties of cross beam in turbulent medium are studied. A cross beam is constructed by the sum of two highly asymmetric Gaussian beams placed along transverse axes. It is known that such beams, when propagating in free space, will exhibit contrasting diffraction behaviours; they expand widely in one axis, while they are almost nondiffracting in the other axis within useful link lengths. This behaviour allows detecting the two components and a sum component if desired separately with a practical multiaperture receiver. Bearing in mind that this property can be exploited for a diversity scheme, our present work focuses on the propagation of such beams in turbulent atmosphere. To this end, starting with a source field expression of the cross beam, the second order mutual coherence function is formulated at the receiver plane. Intensity plots describing the dependence on the source and propagation parameters on the receiver plane are provided. The results tend to confirm the applicability of the concept provided the design parameters are appropriately chosen. For a decisive assessment, however, turbulence-induced beam wander must also be examined.
Rate averaging in free space optics systems using incoherent sources
(Spie-int Soc Optical Engineering, 2004) Baykal, Y
Effect of the information rate on the scintillation index is examined for free space optical (FSO) broadband access applications that use spatially incoherent sources. For this purpose, intensity fluctuations are formulated indicating the effect of the rate on the scintillation index in the presence of the atmospheric turbulence. The bandwidth of modulation of the incoherent source is taken to be much smaller than the carrier frequency, i.e., narrowband approximation is employed. Rate averaging factor for spatially incoherent source is derived as to represent the averaging in weak atmospheric turbulence due to rate of modulation of the intensity. It is found that the scintillations decrease as the rate of transmission through atmospheric turbulence increases. This decrease is independent of the carrier wavelength of the FSO system but depends on the outer scale of turbulence. Up to 10 Gbps, the decrease is negligible for realistic outer scale values. When extremely large eddies are present in the formation of turbulence, rate can be effective in the reduction of the scintillations even at rates up to 10 Gbps. In the limit when the information rate is taken as zero, our results correctly reduce to the known scintillations for spatially incoherent monochromatic excitation.
Relations Among Emotional Mood State Personality Dimensions and Social Desirability in Older Adults
(Gunes Kitabevi Ltd Sti, 2018) Kaynak, Hande; 101097
Introduction: Previous studies have shown that older adults report higher levels of positive affect (PA). Studies in the context of the five-factor model of personality have also noted the age-related changes in personality. However, the possible influence of personality on emotional state needs further investigation in older adulthood. This study examines relations among personality traits, social desirability, and positive/negative affectivity in conjunction with aging. Materials and Method: A total of 123 volunteers (62 young and 61 older adults) was participated in the study. A cross-design was used with consecutive sampling. All participants had higher education. Participants completed the Positive and Negative Affect Schedule as a measure of emotional state. Thereafter, they rated the degree to which each item described themselves on the Five-Factor Personality Inventory, which measures personality dimensions and social desirability. Results: Independent t-tests were conducted to compare young and older adults in terms of affectivity and personality. Findings revealed that older adults reported less negative affect (NA) compared with young adults. Older adults scored higher on agreeableness, conscientiousness, and social desirability, whereas young adults scored higher on extraversion and neuroticism. Based on correlational results, neuroticism was negatively correlated with extraversion, social desirability, and PA in older adults. Analyses of variance showed that conscientiousness, neuroticism, and social desirability impacted positive/negative affectivity. Conclusion: The results indicated that neuroticism proved to be the most important factor on emotional well-being. Older adults low on neuroticism experienced less NA. Furthermore, conscientiousness and social desirability had strong effects on PA indicating that the age-related differences found in affectivity might not only be attributable to age-related changes in personality, but also partly attributable to age-related increases in social desirability.

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