An inverse problem related to an arbitrarily shaped impedance cylinder buried in a dielectric cylinder

Ters saçılma teorisinde yanına yaklaşılamayan cisimlerin fiziksel özelliklerinin belirlenmesi önemli bir araştırma konusu olarak bilinmektedir. Bu çalışmada, iki boyutta keyfi bir şekle sahip dielektrik silindir içerisine gömülü keyfi şekilli bir cismin üzerinde tanımlanan inhomojen empedans fonksiyonunun saçılan elektromagnetik alan verisinden yararlanılarak bulunması için sınır integral denklemlerin çözümüne dayanan bir metod önerilmiştir. İntegral denklemler bir potansiyel yaklaşımı altında türetilmiştir. Bu bağlamda saçılan ve toplam alanlar, içerisinde kaynak (yoğunluk) ve Hankel fonksiyonları içeren integral gösterilimler şeklinde tek-katman potansiyelleri ve bunların kombinasyonları kullanılarak ifade edilmiştir. Fiziksel olarak tek-katman potansiyelleri üzerinde monopollerin bulunduğu bir katmana karşı gelmekle beraber homojen Helmholtz dalga denklemini ve Sommerfeld radyasyon koşulunu sağlar. Problemin çözümünde dielektrik silindirin içerisindeki ve dışarısındaki aynı türden magnetik özellik gösteren basit ortamlara ait dalga sayılarının, silindirlerin şekillerinin ve yakın/uzak saçılan alan verisinin bilindiği varsayılmıştır. Empedans fonksiyonunun bulunabilmesi için her bir bölgedeki elektromagnetik alanların hesabına yönelik yeni bir algoritma sunulmuştur. Saçılan alandan saçıcıların üzerinde tanımlı yoğunluk fonksiyonlarının kararlı ve yaklaşık çözümlerini elde edebilmek amacıyla kötü-kurulmuş integral denklemler Tikhonov anlamında değerlendirilmiştir. Yoğunluk fonksiyonlarının bulunması,  dielektrik silindir içerisindeki toplam alanı hesaplanabilir kılmış ve uygun sıçrama koşulları altında empedans fonksiyonu empedans sınır koşulundan en küçük kareler yöntemi ile elde edilmiştir. Önerilen metodun uygulanabilirliği ve etkinliği nümerik deneylerle test edilmiş ve başarılı sonuçlar elde edilmiştir. Anahtar Kelimeler: Ters saçılma, empedans sınır koşulu, sınır integral denklemleri. Main research areas of inverse scattering theory is the reconstructions of geometrical (location and shape) and / or physical (dielectric permittivity, conductivity, impedance etc.) properties of inaccessible obstacles from the knowledge of the scattered waves (electromagnetic, acoustic, elastic etc.) at large distance. Radar / sonar applications, medical tomography, geophysical exploration and non-destructive testing lead to this type of problems. Motivated by the applications researchers proposed different types of solution methods for the mentioned problems especially after the II.World War. Impedance boundary condition is used to simplify scattering problems involving complex structures. Such that in electromagnetics, imperfectly conducting scatterers, perfectly conducting objects with a penetrable or absorbing boundary layer can be modeled by an impedance boundary condition. In this context, one can study with a simpler model for complex typed structures. The aim of the direct scattering problem for an impedance cylinder is to obtain scattered near- or far-field data for given shape of the cylinder, the impedance function and the wave number of the background medium in the case of an electromagnetic wave illumination. However in the inverse problem case one recovers the impedance function defined on the cylinder from the knowledge of scattered field, shape of cylinder and wave number of the host medium. In this study, we considered an inverse scattering problem for arbitrarily shaped cylindrical objects that have inhomogeneous impedance boundaries and are buried in arbitrarily shaped cylindrical dielectrics. This consideration is realistic, since the problem will have many possible practical applications. For example, in the non-destructive testing of a coating on a wire; the coating is characterized by an inhomogeneous lossy cylinder layer and the conducting wire is modeled by an inhomogeneous surface impedance, or in biomedical applications; the bone of the arm can be modeled in terms of an impedance boundary condition while the muscular structure over it, can be considered as an inhomogeneous lossy cylindrical layer. For the sake of brevity we assume cylinders are infinitely long and illuminated by a TM polarized electromagnetic wave whose electric field vector is always parallel to -axis. Due to the symmetry and homogeneity along the -axis the total electric field vector will be polarized both inside and outside of the cylinder parallel to the -axis. Then the problem is reduced to a scalar one in terms of total fields that have to satisfy homogeneous Helmholtz equation. In order to determine inhomogeneous impedance function we have to reconstruct the field occuring in the interior domain of the dielectric cylinder. Therefore since layer potentials are the solutions of homogeneous Helmholtz equation and they satisfy Sommerfeld radiation condition we use a potential approach to represent fields in every domain via single-layer potentials. Then the far-field expression can be obtained from the asymptotic representation of the scattered field. We note that one can use these representations under proper assumptions for the wave numbers. Roughly speaking, layer potentials are the integrals defined over the boundary of the scatterers which contain Hankel and density (source) functions. In our problem we define two density functions on the boundary of the exterior cylinder and one density function on the buried obstacle. Afterwards, one of the densities on the exterior cylinder can be reconstructed from the solution of an ill-posed far-field equation with measured far field pattern as a data via Tikhonov regularization. The rest two unknown densities are found from the integral equation system obtained by using dielectric (transmission)conditions which ensure the continuity of the fields and their normal derivatives across the boundary of the exterior cylinder. However the compactness of the operators in the system expresses its ill-posedness. Therefore to obtain a stable solution of the system for the densities we apply Tikhonov regularization. Now one can read off the values of the impedance function by substituting interior total field values to the standard impedance boundary condition using jump relations. However, the reconstruction of the impedance function will be sensitive to errors. In order to obtain stable reconstructions we express the unknown impedance function in terms of basis functions and apply least squares approximation. Furthermore, we test the applicability and the effectiveness of our inversion method with noisy data and obtain satisfactory numerical results as illustrated in the last section of the paper. Keywords: Inverse scattering, impedance boundary condition, boundary integral equations

Does the presence of arthroscopically detected stage 1-2 glenohumeral osteoarthritis have any clinical impact on the outcome of arthroscopic rotator cuff repairs?

MakaleWOS:000941667500026PubMed ID: 36945963Background/aim: Rotator cuff rupture (RCR) and glenohumeral osteoarthritis (GHO) are two common disorders of the shoulder joint. However, there are very few reports that examine the relationship between them. This study aimed to present at least two years' clinical results of arthroscopic rotator cuff repair of full-thickness and massive tears accompanied by arthroscopically detected early-stage osteoarthritis.Materials and methods: From August 2016 to December 2017, three hundred and twenty patients with total or massive rotator cuff tears were evaluated retrospectively. Thirty-five patients who were determined as stage 1 and 2 according to the Outerbridge scale for cartilage lesions were found appropriate for investigation. Patients were assessed using the University of California Los Angeles (UCLA) score, and a visual analog scale (VAS) score before surgery and at the final follow-up. The American Shoulder and Elbow Surgeons (ASES) shoulder score was used to evaluate the final outcomes and compare the UCLA shoulder scores.Results: The UCLA scores increased from the preoperative value of 19.1 +/- 3.2 to 29.8 +/- 4.8 at the last follow-up and increased by an average of 10.7 +/- 6.0 (p < 0.001). The median VAS score decreased from the preoperative value of 3.0 to 1.0 (p < 0.001). Besides, the mean ASES score was found as 80.2 +/- 10.6. An excellent positive correlation was found between postoperative UCLA scores and ASES scores (r = 0.887; p < 0.001).Conclusion: To the best of our knowledge, this is one of the first arthroscopic comparative studies about the effect of early glenohumeral osteoarthritis on clinical outcomes after rotator cuff tear treatment. Finding good and excellent results up to 71% after RCR repair in patients with early-stage osteoarthritis was an indication that arthroscopic repair could be planned as the first-line treatment option for RCR pathologies in patients with early-stage degenerative arthritis without considering the rerupture rate.Department of Public Health, Gazi University Medical Facult

Comparison of standardized uptake values obtained from two- and three-dimensional modes of fluorine-18 fluorodeoxyglucose PET-CT in oncological cases

PURPOSEWe investigated the usability of standardized uptake values (SUV) obtained from both two- and three-dimensional (2D and 3D) positron-emission tomography and computed tomography (PET-CT) imaging, and compared the images obtained from these techniques in terms of image quality, lesion detectability, and the presence of artifacts. MATERIALS AND METHODSImage data from 100 patients, who had undergone two PET imagings obtained in 2D and 3D mode after a low dose CT, were evaluated prospectively. Subjective analysis of 2D and 3D images was performed by two readers evaluating the following criteria: overall image quality, detectability of each identified lesion, and the presence of artifacts. The lesions recognized by the readers were also analyzed quantitatively by measuring SUV values. RESULTSThere was a significant difference between the SUVs obtained in 2D and 3D modes. Regardless if the first scan was performed in 2D or 3D mode, the values obtained from 3D imaging were significantly lower than those obtained from 2D imaging (mean SUVmax was 10.48±7.57 for 2D, and 9.66±6.93 for 3D, P < 0.001). Visual analysis did not reveal significant differences regarding lesion detectability between two modes. CONCLUSIONIn oncological PET-CT applications, SUV values are significantly lower in 3D compared with 2D mode. Thus when serial scanning is needed to evaluate response to therapy in the same patient, the imaging modality should be taken into account and performed with the same method to avoid misinterpretation. Additionally, 3D PET-CT imaging can be used instead of 2D PET-CT due to its shorter scanning time without loss of lesion detectability

Comparison of CT and PET-CT based planning of radiation therapy in locally advanced pancreatic carcinoma

Abstract Background To compare computed tomography (CT) with co-registered positron emission tomography-computed tomography (PET-CT) as the basis for delineating gross tumor volume (GTV) in unresectable, locally advanced pancreatic carcinoma (LAPC). Methods Fourteen patients with unresectable LAPC had both CT and PET images acquired. For each patient, two three-dimensional conformal plans were made using the CT and PET-CT fusion data sets. We analyzed differences in treatment plans and doses of radiation to primary tumors and critical organs. Results Changes in GTV delineation were necessary in 5 patients based on PET-CT information. In these patients, the average increase in GTV was 29.7%, due to the incorporation of additional lymph node metastases and extension of the primary tumor beyond that defined by CT. For all patients, the GTVCT versus GTVPET-CT was 92.5 ± 32.3 cm3 versus 104.5 ± 32.6 cm3 (p = 0.009). Toxicity analysis revealed no clinically significant differences between two plans with regard to doses to critical organs. Conclusion Co-registration of PET and CT information in unresectable LAPC may improve the delineation of GTV and theoretically reduce the likelihood of geographic misses.</p

Bileşik ısı güç üretim sistemi ve sanayi modellerine uygulanması

Teknolojik açıdan gelişmemiş ülkelerin en önemli dezavantajları, kendi yapılarına uygun enerji politikalarını belirleyememiş olmalarıdır. Bu açıdan gelişmekte olan ülkemiz de sağlıklı bir enerji politikasına sahip olmadığı gibi, enerji kaynakları bakımından da zengin bir ülke değildir. Son yıllarda enerjinin üretim ve kullanım aşamasında verimliliğin arttırılması, kayıpların en az düzeyde tutulması daha fazla önem kazanmaya başlamıştır. Hızla artan enerji gereksinimi, daha ekonomik enerji kullanımı arayışlarını arttırmış ve böylece yüksek verimli kojenerasyon tekniği çözümleri gündeme gelmiştir. Ülkemizde de özellikle tekstil, kağıt, seramik, çimento, kimya, gıda, toplu ısıtma ve soğutma gibi hem elektrik hem ısıya gereksinim olan enerji yoğun sektörlere de bu sorun yansımıştır. Kojenerasyon yani bileşik ısı-güç sistemleri, bir tek enerji kaynağından ısı ve elektrik enerjilerinin birlikte üretilmesidir. Kojenerasyon proseslerinde, normal olarak bir enerji şeklinin üretiminde kaybedilen ısı geri kazanılır. Bu ısı, daha sonra ikinci enerji şeklini hasıl etmek için kullanılır. Bu yöntemle üretim şekli, ısı ve elektriğin ayrı farklı yerlerde üretilmesinden daha iyi ekonomik sonuçlar doğurmaktadır. Enerji üretiminin, tüketimin olduğu merkezlerin yakınlarında gerçekleştirilmesi, kullanılabilirlik ve ekonomik açılardan daha uygun olacaktır. Bu tezde kojenerasyon sistemlerinin teknik ve ekonomik açılardan olabilirliği incelenmiş ve örnek bir sanayi projesi geliştirilmiştir. Anahtar kelimeler: Bileşik ısı-güç, kojenerasyon TEZ SAVUNMA JÜRİSİ 1. Prof. Dr. Ayşen HAKSEVER T.Ü. Çorlu Makine Mühendisliği 2. Prof. Dr. Bahattin AKDEMİR T.Ü. Zir. Fak. Tarım Mak. A.B. Dalı 3. Yrd. Doç. Dr. Semih ÜZE T.Ü. Çorlu Makine Mühendisliği Combined Heat and Power System and Industrial Applications SUMMARY The most important disadvantages at the undeveloped countries which are in respects of technology, don't have suitable energy policy. From this point Turkey has not suitable energy policy and isn't rich in terms of energy. Increasing efficiency of energy in production and usage, and decreasing energy losses as much as possible begin to gain more importance in last years. Recently, there is increasing demand in the energy needs and parallel to this trend, there is also a decrease in sources of petroleum products, natural gas, coal reserves. Because of this fact, the choice of efficient use of primary energy sources and environmental-friend systems are a must. This phenomena has been naturally linking the solution techniques of high efficient co-generation systems. As a result, this causes to defect the demand and supply balance in the energy dense sectors such as textile, paper, ceramic, cement, chemical, food, central heating/cooling industries in Turkey. Combined heat and power (CHP) plants are the sequential production of thermal and electric energy from a single fuel source. In the cogeneration process, heat is recovered that would normally be lost in the production of one form of energy. That heat is then used to generate the second form of energy. The economical performances of these plants are higher than those of plants in which electricity and heat are generated at the different places. Construction of energy production plants which are near the energy consumption places will be more suitable for usage and economic points of view. The applications of cogeneration systems in terms of technical and economical approach have been reviewed and an industrial project sample has been improved. Keywords:Combined heat and power, cogeneration

Reconstruction algorithm for impenetrable rough surface profile under Neumann boundary condition

In this paper, an algorithm to reconstruct one-dimensional impenetrable rough surface from the knowledge of scattering field is presented. The rough surface is considered as locally perturbed and the scattering field data are collected above the roughness in a simple non-magnetic medium considering Neumann boundary condition. First, the surface integral equation constituted via the Neumann boundary condition is solved and scattering field data are observed synthetically. Then, the same surface integral equation together with the data equation are solved in an iterative fashion to reconstruct the surface variation. In the numerical implementation, the so-called ill-posed inverse problem is regularized with Tikhonov method and a least-squares solution is obtained by using Gaussian-type basis function. Finally, numerical examples are carried out to illustrate effectiveness of the method.Publisher's Versio

Image recovery of inaccessible rough surfaces profiles having impedance boundary condition

This letter addresses a reconstruction algorithm of locally rough inaccessible surface profiles via the knowledge of the scattered field data under the consideration of the impedance boundary condition (IBC). To this aim, first, the synthetic scattered field data are obtained through the solution of the conventional surface integral equation (SIE) written on the rough surface. Then, the same SIE together with the data equation is solved iteratively via Newton's method to obtain the image of the rough surface profile. In the numerical implementation, the nonlinear ill-posed inverse problem is linearized in an iterative fashion via the Newton method and regularized by Tikhonov in the least-squares sense. The feasibility of the algorithm is provided via numerical examples, which shows that the method is effective and promising.Publisher's Versio