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Grinding mechanism of sepiolite for high viscosity industrial applications
Get PDFBu çalışmada yaş ve kuru olarak uygulanan farklı öğütme tekniklerinin sepiyolit liflerini serbestleştirmedeki etkinliği boyut kontrolu ile birlikte araştırılmıştır. Katı konsantrasyonu, karıştırmanın şiddeti-süresi ve öğütme şeklinin sepiyolitin reolojik özellikleri üzerinde onemli etkisinin olduğu görülmüştür. Kuru öğütme işlemlerinin öğütme süresindeki artışla beraber sepiyolitin yapısına zarar verdiği ve 2 saatlik öğütme süresinden sonra tekrar floklaşmadan dolayı tane boyutunun irileştiği ve lifsi yapısının kaybolduğu, yerini şekilsiz kürelerin aldığı görülmüştür. Yaş öğütmede ise sepiyolitin lifsi yapısının korunduğu tespit edilmiştir. Elde edilen verilerin değerlendirilmesinde zeta potansiyel, yüzey alanı ve SEM (taramalı elektro mikroskop) görüntülerinden faydalanılmıştır. Anahtar Kelimeler: Sepiyolit, öğütme, viskozite.Clay minerals have a wide range of industrial applications including thickeners and flow regulators which are known as rheological additives. For this purpose, bentonite type layered smectite group clays and needle structured sepiolite and attapulgite type clays are used. The mechanisms of gelling for both clays are different due to their unique structures. The rheological properties of these suspensions depend on such parameters as concentration, the intensity of agitation and pH. These properties make sepiolite suspensions very useful thixotropic materials and thickeners. In this study, the effect of mode of grinding, dry and wet on disintegration of sepiolite fibers was investigated under controlled particle size. Physical parameters are shown to impart a pronounced effect on the viscosity of sepiolite; the viscosity increases with increasing the energy of agitation, but increase in viscosity against solids concentration is not linear but polynomial. The results were interpreted with zeta potential, surface area measurements and SEM photographs. It is shown that the mode of grinding has a significant effect on the rheological properties of sepiolite. Dry grinding process adversely affects the structure of sepiolite and after 2 hours of grinding, the grain size is enlarged due to agglomeration of fibers into spheres. In wet grinding, the fiber structure of sepiolite was preserved along with a plausible size reduction. These results were also corroborated with zeta potential results. Keywords: Sepiolite, grinding, viscosity
New Statistical downscaling methods and applications for Turkey
Get PDFHava ve iklim süreçlerinin yeryüzündeki yaşam üzerinde hayati etkileri vardır. İklim değişkenliği ve değişiminin anlaşılabilmesi, bölgesel ve yerel iklim tanılarının geliştirilmesi, iklim çalışmalarının temel konularından biridir. İklim etkilerini araştıranlar genelde iklim değişiminin ve değişkenliğinin geçmişi, bugünü ve geleceği hakkında detaylı ve doğru bilgilere gereksinim duyarlar. İklim değişimi ve değişkenliği konusunda önemli ve temel araçlar genel dolaşım modelleridir (GDM). Ne yazık ki kaba sayısal çözünürlük üzerinde çalıştırılan GDM’ler yerel iklim değişimi ve değişkenliği hakkında doğru bilgi veremezler. Bu bağlamda, GDM’lerin kısıtlarından dolayı “ölçek küçültme” stratejilerinin geliştirilmesine gerek vardır. İklim araştırma ve etkilerinin arasındaki farklı ölçekler; “ölçek küçültme” ve “ölçek büyültme” yaklaşımları ile birbirine bağlanabilir. Bu çalışma, yeni ölçek küçültme yöntemlerini geliştirme ve Türkiye üzerine uygulanması konusunda ilk ve tek araştırmadır. Anahtar Kelimeler: Bölgesel, genel dolaşım modeli, iklim etki, ölçek küçültme, Türkiye, yinelemeli yapay sinir ağları.Weather and climate have a profound influence on life on earth. Understanding climate variability and climate change reveals the increasing need for improving regional and local-scale climate diagnosis which is one of the main goals of climate research. The climate impact researches usually require accurate and detailed climate information on yesterday, present, and tomorrow with high resolution space scale. The main and important tools of studying climate are general circulation models (GCMs). Unfortunately, GCMs running on coarse resolution may not be able to detect the local scale climate variability. The spatial-scale mismatch between climate research and climate impact studies has to be bridged by ?downscaling? on the side of the climate research and ?upscaling? on the side of the climate impact research. This study is the first research of developing downscaling strategies over Turkey. Two new downscaling strategies for climate diagnosis are developed in this study. The proposed methods are based on artificial recurrent neural networks (RNN) and multivariate statistical techniques that derive transfer functions from the large-scale free troposphere variables of which are assumed to govern the local climate over Turkey. This study presents two new approaches for downscaling monthly near-surface air temperature and total precipitation for Turkey stations by surface large-scale pressure systems and upper air circulations derived from National Centers for Environmental Prediction- National Center of Atmospheric Research (NCEP-NCAR) Reanalysis data sets. Keywords: Regional, general circulation model, climate impact, downscaling, Turkey, artificial recurrent neural networks
Model support system for rural non-point sources and local implementation
Get PDFKırsal havzalarda sürdürülebilir kalkınma için yayılı kaynak modellerinin bir araç olarak kullanılabilmesi gerekmektedir ve çalışmada buna yönelik bir modelleme destek sistemi oluşturulmuştur. Sistemin Türkiye özelinde uygulanabilmesine rehberlik edici bir örnek çalışma Köyceğiz-Dalyan havzasında yapılmıştır. Uygulamada, kırsal kesime özel, gelişkin bir modelleme destek sistemi kurmak için gerekli sistematik yaklaşım, uygulama güçlükleri ve bunların telafi yöntemleri üzerinde yoğunlaşılmıştır. Türkiye’de kırsal alanlardaki yayılı kaynakların modellenmesi için, projelerin baştan sona yönetimine dair hem yöneticilerin ve hem de araştırıcıların faydalanabileceği kapsamlı bir dokümantasyon oluşturulmuştur. Öte yandan, Türkiye’de nadiren uygulanmış HSPF (Hydrological Simulation Program-FORTRAN), modelleme sürecinde kullanılarak bir hidrolojik model zemini de geliştirilmiştir. Anahtar Kelimeler: Kırsal yayılı kaynak kirliliği, HSPF, havza modelleme, hidroloji, toprak analizleri, meteoroloji. This study deals with developing a model support system for non-point source modeling, which is a vital tool for sustainable management of rural basins. Guidance on developing this system is provided via a case study over Köyceğiz-Dalyan Watershed, in Turkey. The case study defines; the systematic approach to establish this system, possible general and local difficulties during application, and workarounds for these problems. Decision-makers, researchers and modelers in Turkey may use this fully documented information to form, propose, initiate, manage, and finalize similar projects on rural area non-point source modeling. HSPF (Hydrological Simulation Program-FORTRAN), which is a sound hydrological model with very rare applications in Turkey, was implemented to develop the core model for prospective use within a much comprehensive watershed model. Although the quantified modeling outputs of this study should be considered as preliminary, they also act as a reliable and timesaving initial step towards a much broader evaluation of the non-point sources in this rural watershed. Given that developing an integrated approach for watershed management is quite a fertile and a rather young concept, this study will nevertheless guide the non-point source modeling process as a tool for the possible implementation of holistic environmental management plans in Turkey.Keywords: Rural non-point source pollution, HSPF, watershed modeling, hydrology, soils analysis, meteorology
Supersymmetric field theories and cohomology
Get PDFBu çalışmada, genel anlamda süpersimetrik alan teorilerinin kohomolojik yapısı çalışılmıştır. Kohomoloji problemi süpersimetri cebri kullanılarak tanımlanmıştır. Süpersimetrik alan teorilerinin eylemlerinin ilgili çokluların en üst elemanı olduğu kullanılarak elde edilen bu kohomoloji probleminin çözümleri yardımıyla bu eylemlerin düşük boyutlu alan polinomlarının çoklu süpervaryasyonları olarak temsil edilebileceği gösterilmiştir. Bu yaklaşımın bir uygulaması olarak Wess-Zumino modelinin kohomolojik yapısı incelenmiştir. Elde edilen sonuçlardan modelin eyleminin kinetik, kütle ve etkileşme terimlerinin kabuk-dışı süpersimetrik durum için tam olarak düşük boyutlu alan polinomlarının kiral ve/veya anti-kiral çoklu süper varyasyonları ile yazılabileceği gösterilmiştir. Anahtar Kelimeler: Süpersimetri, süpersimetrik alan teorileri, kohomoloji.In this work, the cohomological structure of supersymmetric field theories is studied in a general context. Cohomology problem is defined by using the off-shell structure of the supersymmetry algebra. In order to define a cohomology problem it is crucial to use the two component (Weyl) formalism of the supersymmetry algebra, since each individual component of chiral and anti-chiral supersymmetry generators are nilpotent operators. It is then possible to show that the actions of supersymmetric field theories belong to a class of solutions of this cohomology problem and can be represented as multiple supervariations of some lower dimensional field polynomials due to the fact that the actions of supersymmetric field theories can be viewed as the highest component of respective multiplets. It is also discussed that the aforementioned algebraic structure can be thought as the algebraic source of the well-known non-renormalization theorems of several supersymmetric field theories. As an application of our method, the cohomological structure of Wess-Zumino model is discussed. It is shown that the kinetic, mass and the interaction terms can be constructed from the chiral and/or anti-chiral supervariations of the lower dimensional field polynomials for off-shell supersymmetry. It is then found out that the well known non-renormalization theorems of Wess-Zumino model is related to the terms that can only be written as pure chiral or anti-chiral supervariations of (mass) dimension three fields. Keywords: Supersymmetry, supersymmetric field theories, cohomology
Towards the classification of scalar non-polynomial evolution equations
Get PDFLiteratürde, “integre edilebilen denklemler”, lineer denklemlere dönüştürülebilen ya da ters spektral dönüşüm ile çözülebilen denklemler olarak tanımlanır (Calogero, 1991). Bilinen tüm integre edilebilen denklemlerin ortak bir özelliğini bulmaya dayalı yöntemlere “integrabilite testleri” adı verilir. Sonsuz sayıda korunan nicelikler, sonsuz sayıda simetriler, soliton çözümleri, yaygın kullanılan integrabilite testlerinden bazılarıdır. “Sınıflandırma problemi”, integre edilebilir diferansiyel denklem ailelerinin sınıflandırılması olarak bilinir. Yakın geçmişte Sanders ve Wang sonsuz sayıda simetrilerin varlığını kullanarak, ölçek bağımsız skaler integre edilebilir, 7 inci mertebeden büyük, evrim denklemlerinin, 3 üncü ve 5 inci mertebeden denklemlerin simetrileri olduğunu göstererek sınıflandırma problemini, polinom ölçek bağımsız skaler denklemler için çözmüşlerdir (Sanders ve Wang, 1998). Keyfi m inci mertebeden evrim denklemlerinin sınıflandırılması hakkında, ilk sonuç Bilge (2005)’te elde edilmiştir. Bu sonuca göre, n=m+1 mertebeden trivial olmayan bir korunan yoğunluğu kabul eden, m=2k+1 ve k≥3 mertebeden evrim denklemleri kuazilineer olmalıdır. Bu çalışmada ise, m=2k+1’inci mertebeden integre edilebilir skaler evrim denklemlerinin, m>7 için, um-i, i=0,1,2 türevlerine göre polinom olduğu ispatlanmıştır. Burada integrabilite testi olarak Mikhailov ve diğerleri (1991) tarafından önerilen “formel simetri”lerin varlığı kullanılmıştır. Bu integrabilite testi, ρ(i) olarak adlandırılan bazı korunan yoğunlukların varlığını gerektirmektedir. Bu çalışmada kullanılan ρ(1), ρ(2) ve ρ(3), genel ifadeleri Bilge (2005)’de verilmiş olan korunan yoğunluklardır. Hesaplamalarda kullanılan genel formüller m≥19 için geçerlidir. m<19, (m=7, 9, 11, 13, 15, 17) için hesaplar sembolik programlama dili REDUCE kullanılarak yapılmış ve aynı polinomluk özellikleri elde edilmiştir. Bu çalışmada sadece için elde edilen sonuçlar sunulmuştur. Anahtar Kelimeler: İntegrabilite, simetri, korunan yoğunluklar.In the literature, integrable equations are meant to be non-linear equations which are solvable by a transformation to a linear equation or by an inverse spectral transformation (Calogero, 1991). The difficulty in constructing an inverse spectral transformation had motivated the search for other methods which would identify the equations expected to be solvable by an inverse spectral transformation. These methods which consist of finding a property shared by all known integrable equations are called "integrability tests". The existence of infinite number of conserved quantities, infinite number of symmetries, soliton solutions are some of well known integrability tests. In the classical theory, "symmetry of a differential equation" is defined in terms of the invariance groups of the differential equation. This definition is essentially equivalent to defining symmetries as solutions of the linearized equation. That is if is a symmetry of the evolution equation then where is the Frechet derivative of F. In this study we work towards the classification of scalar non-polynomial integrable evolution equations of order , using the "formal symmetry method". This integrability test is based on the existence of a truncated expansion of a formal pseudo-differential operator R satisfying the operator equation. The classification problem for scalar, polynomial, scale invariant integrable equations is solved in the work of (Sanders and Wang, 1998), where it is shown that integrable equations of order greater than or equal to seven are symmetries of third and fifth order equations. In subsequent papers these results are extended to the cases where negative powers are involved (Sanders and Wang, 2000), but more general non-polynomial equations are not studied by their method. The "formal symmetry" method introduced by (Mikhailov etal., 1991) have been used to obtain a preliminary classification of essentially non-linear third order equations and quasi-linear fifth order equations. The classification of essentially non-linear third order equations is considered later in the work of (Heredero etal., 1995), where quasilinear integrable equations that are not linearizable are found to be related to the Korteweg-de-Vries and Krichever-Novikov equations through differential substitutions. The first result towards a classification for non-polynomial m'th order evolution equations is obtained in (Bilge, 2005) where it is shown that scalar evolution equations , of order with , admitting a conserved density , with P 0, of order , are quasi-linear. The method of (Bilge, 2005) is not applicable to third order equations, because for m=3, the canonical conserved density , which the quasilinearity result is based on, is not of the generic form. For m=5, although the generic form of is valid, k=2 occurs as an exception and we cannot exclude the existence of fifth order non-quasilinear integrable equations, at least with the present method. For the structure of integrable equations seems to be much simpler and one may hope to obtain a complete classification. In the present work we continue with the classification problem using formal symmetries and we prove that arbitrary (non-polynomial) scalar evolution equations of order that are integrable in the sense of admitting the canonical conserved densities and introduced in (Mikhailov vd., 1991), are polynomial in the derivatives for . These results have been obtained by the computation of , i=1,2,3, where we used only the coefficients of top two nonlinear terms. First we proved that the top two nonlinear terms come from top 4 derivatives in the expansion of and we obtained the expressions of the coefficients of these top two nonlinear terms. Then we computed successively these coefficients for each case. These results are valid for , thus for the completeness of the proof we repeated the computations explicitly for the lower orders namely and obtained the same results which are omitted here. Keywords: Integrability, symmetry, conserved density
Synthesis and solution studies of new quaternary azaphthalocyanines
Get PDFTetrapirazinoporfirazinin yaygın olarak kullanılan diğer isimlendirilmesi ‘azaftalosiyanin’dir. Bu çalışmada, periferalde heteroatom olarak S-sübstitüe simetrik metalli ve metalsiz azaftalosiyaninler ve suda çözünür katyonik türevleri sentezlenmiştir. Metalli AzaPc’ler ftalosiyaninler gibi sentezlenen ligandtan doğrudan uygun metal tuzları mevcudiyetinde siklomerizasyonla ya da porfirazinler gibi metalsiz türeve metal girmesiyle kolaylıkla hazırlanabilir. Metalsiz AzaPc’ler dilityum veya magnezyum AzaPc’den zayıf veya kuvvetli asit kullanılarak elde edilebilir. Başlangıç maddesi olarak 5,6-dikloropirazin-2,3-dikarbonitril 1 seçilmiştir ve diaminomaleodinitrilden (DAMN) iki adım reaksiyon ile kolaylıkla hazırlanmıştır. Elde edilen 5,6-dikloropirazin-2,3-dikarbonitril 1, pirazin-2,3-dikarbonitril kısmı ve klorür atomlarının güçlü elektron çekme özelliğinden dolayı 5 ve 6 pozisyonundan nükleofillerle kolay sübstitüsyona uğrar. Hedeflenen ligandı sentezlemek için, 1 bileşiği 2-dimetilaminoetantiyol hidroklorür ile oda sıcaklığında muamele edilmiştir. Azaftalosiyanin 3, magnezyum propanolat varlığında yüksek verimde sentezlenen 2 bileşiğinin tipik siklotetramerizasyon reaksiyonu ile hazırlanmıştır. Metalsiz AzaPc 4, magnezyum AzaPc 3’ün trifloroasetik asit ile muamelesiyle hazırlanmıştır. Çinko AzaPc 5’in sentezi, metalsiz AzaPc 4’ün, çinko (II) asetat ile reaksiyonundan elde edilirken, kobalt AzaPc 6 ftalosiyaninlerdeki olduğu gibi 5,6-bis(2-dimetilaminoetilsülfanil)-2,3-disiyanopirazin 2 bileşiğinin direkt kobalt (II) asetat ile reaksiyonundan sentezlenmiştir. Bu azaftalosiyaninler suda çözünür kuaternize ürünlere metil iyodür ile reaksiyon sonucu dönüştürülmüştür. Agregasyon olayı, belirli bir pH aralığında dimetilamino sübstitüe magnezyum azaftalosiyanin için incelenmiştir. Elde edilen bu bileşikler FT-IR, 1H NMR, kütle ve UV-Vis spektral değerleriyle karakterize edilmiştir. Anahtar Kelimeler: Azaftalosiyanin, agregasyon, pirazin.Tetrapyrazinoporphyrazines (TPyPzs) are the structures that are formed from the annulation of four pyrazine rings to the porphyrazine (Pz) framework. Other extensively denomination use of TPyPz is "azaphthalocyanine"(AzaPc). In comparison to phthalocyanines (Pcs), the eight additional nitrogen atoms in TPyPzs induce large electronic effects on the structure. AzaPcs are formed by cyclotetramerisation of pyrazine-2,3-dicarbonitrile or its substituted derivatives. Like Pcs, AzaPcs can be substituted in their peripheral 2,3-positions. This situation may further enhance their solubility of substituted TPyPzs and their metal complexes in organic solvents and also influence the electronic excitation energies of these compounds. The TPyPzs have specific optical properties because they have symmetrical rich 18 p-electron aromatic macrocycle, which can play host to different metal ions in its central cavity. Therefore, they have been extensively used in optical recording media, photosensors, optical filters and copy preventing inks. In this work, octasubstituted symmetric metallo and metal-free azapcs containing sulphur as heteroatom on the periphery and their cationic derivatives that are soluble in water were synthesized. Metallo azapcs can be readily prepared either by a direct cyclotetramerisation of dinitrile precursors like Pcs or by a metal insertion into metal-free derivative as Pzs in the presence of corresponding metal salts. Metal-free azapcs can be obtained from either dilithium or magnesium azapc using weak or strong acid. For this porpuse, 5,6-dichloropyrazine-2,3-dicarbonitrile 1, that is easily accessible from diaminomaleodinitrile (DAMN) in a two step reaction, was chosen as a starting material. Because of the strong electron withdrawing ability of cyano and chlorine atoms, this compound undergoes ready substitution in positions 5 ve 6 with nucleophiles like primary and secondary amines, alcoholates, thiolates. Consequently, treating 1 with 2-dimethylaminoethanthiol hydrochloride at room temperature afforded 2 in rather high yield. In order to convert to ligand 2 into azapc 3, we made use of its template reaction in the presence of magnesium propanolate. Mg azapc 3 was crystallized from ethanol/water. Treatment of Mg azapc 3 with trifluoroacetic acid gave the metal-free azapc 4. Zinc azapc 5 was prepared through the insertion of Zn ion into metal-free azapc 4. However, the cobalt azapc 6, was directly synthesized by cyclotetramerization of 2 in the presence of anhydrous cobalt acetate. When azapcs 3 and 4 were treated with methyliodide in chloroform, the hygroscopic azapc products 7 and 8 with eight quaternary ammonium groups were obtained. The new compounds were characterized by using standard spectral methods (elemental analysis, 1H NMR, UV/Vis, IR and Mass spectroscopy). From the FT-IR spectrum of 2 , the characteristic stretching vibrations of CºN group was observed at 2232 cm-1. When the precursor 2 was converted into new metallo or metal-free azapcs (3, 4, 5, 6), this sharp peak disappeared as a proof of the cyclotetramerization reaction of dinitrile. IR spectra of azapcs 3, 5 and 6 is similar to the IR spectrum of dinitril compound 2. In the IR spectrum of 4 the NH groups in the inner core give absorption at 3292 cm-1. Besides, no major change in the IR spectra was found after quaternization. In the 1H NMR spectrum of compound 2 (CDCl3), the aliphatic protons are observed at 3.38(S-CH2), 2.63(N-CH2) and 2.30 (CH3) ppm. 1H NMR spectra of 3 and 4 are almost the same as compound 2. However, 1H NMR spectrum of metal-free azapc 4 shows an additional peak at -3.32 ppm due to NH groups in the inner core. Furthermore, in the mass spectrum, we observed the molecular ion peaks at m/z: 337.10 for 2 and at m/z: 1410.7 for 5 which confirm the proposed structures. In the electronic absorption spectra of the complexes (3, 5 and 6), Q bands were observed at 644, 644 and 648 nm, respectively in CHCl3. The D2h symmetry of the metal-free azapc 4 is verified by two broad absorptions in the visible region (633-658 nm). A second intense and broad p-p* transition in the range 358-373 nm which is called Soret or B band is also a characteristic band as expected for tetrapyrroles. When the UV-Vis spectra of quaternized products 7 and 8 were analyzed in aqueous solution. Besides, in this study aggregation properties that can be observed at UV-vis spectrum of Mg azapc 3 were investigated by the dropwise addition of 0.01 M HCl to their THF solution. Keywords: Azaphthalocyanine, aggregation, pyrazine
State reduction of incompletely specified finite sequential machines
Get PDFBu çalışmada, kısmen belirli ardışıl makinelerde durum indirgeme konusu ele alınmıştır. Durum indirgeme için geliştirilen algoritmalar, Boole fonksiyonlarının birlikte indirgenmesi, durum kodlama ve tek koşullu örtü problemi çözme gibi lojik tasarımın diğer adımlarına da uygulanmıştır. Bu çalışmada kullanılan kapalı yollar kümesi kavramına ve bu kümeden minimal kapalı örtü elde etmeye dayanan bir yönteme literatürde rastlanmamıştır. Bu algoritmalara dayanan, SRC (State Reduction and Covering) programı geliştirilmiştir. SRC, MCNC ve diğer bençmarklarda Rho yöntemi (Rho vd., 1994) ve Puri yöntemi (Puri ve Gu, 1993) ile karşılaştırılmıştır. Test sonuçlarından da görüldüğü gibi SRC programı özellikle kritik bençmarklarda daha iyi sonuç vermiştir.Anahtar Kelimeler: lojik tasarım, algoritma, durum indirgeme, örtü problemi.This paper is concerned with the problem of synthesizing a class of digital circuits, sequential circuits, more specifically state reduction of of incompletely specified sequential circuits. State reduction is an important step in the design of the synchronous and asynchronous sequential circuits. The algorithms which are developed for state reduction, are also applied to other steps of the logic synthesis, such as multiple-output Boolean minimization, state encoding and unite/binate covering problems. In this paper three algorithms are presented to find a minimal equivalent of a given incompletely specified finite sequential machine. These algorithms use a new concept; closed paths constituted by compatibles or prime compatibles. This closed paths concept and an algorithm which uses this concept is not observed in the literature. These algorithms are implemented in an efficient computer program SRC (State Reduction and Covering). SRC is run and tested on several FSMs including the MCNC FSM benchmarks and the results are given in conclusion. From the test results, it can be seen that, despite of the limited computing resources, SRC is more efficient on all benchmarks, especially on the critical benchmarks. Using these algorithms, MORP (Multiple Output Reduction Program) developed to realize m Boolean functions with n variables. State reduction methods which are developed in this work, are also applied to state encoding problem and a computer program, OPASKOD (Race-free State Assignment Program) developed.Keywords: logic synthesis, algorithm, state reduction, covering problem
Frequency and time domain characteristics of linearly phased/sequentially excited periodic arrays of dipoles
Get PDFDoğrusal fazlı/sırayla uyarılan periyodik dipol dizilerinin frekans ve zaman domeni yanıtları, Floquet dalga ve eleman-eleman toplama gösterilimleri kullanılarak incelenmiştir. Her bir dipolün katkısının ayrı ayrı hesaplanıp toplanması ile bulunan eleman-eleman toplama yönteminin yakınsaklık özelliklerini iyileştiren bir formülasyon geliştirilmiştir. Periyodiklik özellikleri kullanılarak, dizinin toplam ışınım alanı için Floquet dalgaları ve sonsuz periyodik bir dizinin sonlandırılmasının etkilerini karakterize eden uç kırınım bileşenlerini içeren alternatif bir formülasyon elde edilebilir ve biri diğerine göre kaydırılmış ve uygun şekilde ağırlaştırılmış iki yarı-sonsuz çizgisel periyodik dizinin farkını alarak sonlu çizgisel diziler modellenebilir. Yukarıda değinilen yaklaşım literatürde incelenmiştir, bu çalışmada önerilen ve yapay açıklık yaklaşımı adı verilen yöntemde ise, Lz kadar kaydırılmış dizinin bir P(x,y,z) gözlem noktasında oluşturacağı alan, diziyi kaydırmak yerine gözlem noktasını zıt yönde kaydırarak, orijinal kaydırılmamış dizinin bir P’(x,y,z-Lz) sanal gözlem noktasında oluşturacağı alan bulunarak hesaplanmaktadır. Önerilen bu yapay açıklık yaklaşımı, çizgisel dipol dizilerinin süperpozisyonu alınarak elde edilebilen her türlü düzlemsel ve üç boyutlu dipol dizisinin etkin biçimde modellenmesinde de kullanılmıştır. Işınım yapan, yapmayan ve kırınan dalga bileşenleri cinsinden ifade edilen Floquet dalga gösteriliminin etkinliğini göstermek için sayısal örnekler verilmiş ve bu sonuçlar eleman-eleman toplama yöntemi ile karşılaştırılıp doğrulanmıştır. Dipollerin geniş bantlı kaynak fonksiyonlarıyla sürüldüğü durumda karşılaşılan konvolüsyon integrallerinin hesaplanması için kaynak fonksiyonuna genlik ve süreleri adaptif biçimde belirlenen parça parça sürekli bir dizi dikdörtgen darbe ile yaklaşıklık yapılmasına dayanan analitik bir yöntem geliştirilmiştir. Anahtar Kelimeler: Green fonksiyonu, Floquet dalgalar, faz farklı anten dizileri, periyodik diziler.In this study, frequency and time domain radiation characteristics of linearly phased/sequentially excited periodic dipole arrays are investigated. Large periodic arrays of short radiating elements have been increasingly investigated for the last decade or so, since they have a vast range of applications ranging from phased array antenna systems with flexible beam steering and very narrow beam forming capabilities, frequency selective surfaces and diffraction gratings to photonic crystal fibers and metamaterials, etc. The field radiated by a sequentially excited/linearly phased dipole array can be calculated via a superposition over the contributions of individual dipoles in the array. This classical approach, called element by element summation, suffers from two shortcom-ings: i) its numerical implementation becomes time consuming and inefficient for large size arrays ii) it does not provide a framework for identification of the mechanisms generating different wave objects (propagating, evanescent, diffracted waves) and their relative weights at given observation points. On the other hand, by taking advantage of the periodicity, the problem can be cast into an alternative formulation wherein the contributions of individual elements are represented collectively in terms of Floquet waves, which are augmented with tip diffracted wave constituents to account for the truncation of a strictly periodic sequence at a large but finite number. The phenomenologies associated with the phased array of dipoles are also related to the oblique plane wave scattering from an array of short wire elements. The obliquity of the incident field with respect to the array plane determines the interelement phasing (time delay) of the radiating array. The field radiated by a finite, periodic line array of dipoles at a given observation point can be synthesized via superposition of shifted and properly weighted replicas of the field radiated by semi infinite line arrays of dipoles. In this paper, we propose a synthetic aperture type approach for calculation of the field radiated by a finite line array of length Lz, wherein the contribution of the shifted semi infinite line array is accounted for by the contribution of the original array at an oppositely shifted virtual observation point P?(x,y,z-Lz). The proposed synthetic aperture approach is also used for the efficient modeling of radiation from structures involving line arrays organized spatially to form planar and 3D ar-rays. In this paper, utilizing the proposed synthetic aperture approach, radiation from linear and planar dipole arrays are calculated and examples of numerical results are presented both in the frequency domain and also in the, heretofore scarcely investigated, time domain. It is shown that when the pulsed excitation has a relatively flat spectra which does not have significant low frequency content, the array response can be calculated in a rather efficient and accurate manner utilizing analytical approximations for the contributions from Floquet wave constituents. High frequency asymptotics can be used for obtaining contributions from all except for the zero indexed Floquet wave which needs to be treated separately and involves the calculation of a convolution. For obtaining the response for wide band dipole excitations, we introduced an accurate analytic approximation technique for calculating the involved convolution integral, which is based on an adaptive windowing scheme wherein the pulse excitation is represented approximately via a set of rectangular pulses with adaptively determined amplitudes and time extends. Following this approach the convolution is synthesized via the contributions from the set of rectangular pulses each of which can be calculated in closed form. The resulting formulation yields substantial reduction in the computation time since the response due to all Floquet wave constituents are calculated analytically, either via high frequency asymptotics or via the weighted sampling approach. The exact solution obtained via element by element summation is utilized as a comparison solution for validating the numerical results calculated via Floquet wave representations. Element by element summation representations suffer from convergence problems which are best illustrated considering the representation for a semi infinite line array. In this context, a method is proposed to substantially improve the convergence properties of the element by element summation approach. In this paper, we have been able to verify that Floquet waves provide a very accurate and efficient representation for calculating time/frequency domain radiation from linearly phased/sequentially excited, large, 1D, 2D and 3D periodic arrays of electric current dipoles. Keywords: Green's function, Floquet waves, phased array antennas, periodic arrays
Effect of particle size and characteristic of waste on waste stabilization: Application of pilot scale simule aerated bioreactor
Get PDFÜlkemizde ve dünyada katı atıkların bertarafı için en yaygın olarak kullanılan yöntem, atıkların depolanmasıdır. Katı atıklar, bu depolama alanlarında anaerobik prosesler sonucu bozunmaktadır. Gerekli önlemlerin alınmaması durumunda, anaerobik bozunma sonucunda depolama alanlarından oluşan sızıntı suyu ve depo gazı çevresel sorunlara neden olmaktadır. Son yıllarda katı atıkların aerobik bioreaktör depolama alanlarında depolanması konusunda araştırmalar ve uygulamalar yaygınlaşmaya başlamıştır. Söz konusu alanlarda, atıklar daha hızlı bir şekilde bozunmakta ve daha kısa sürede stabil hale gelmektedir. Aerobik bioreaktör depolama alanlarında oluşan sızıntı suyu miktarlarında azalma sağlanırken kalitesinde artış gözlenmektedir. Metan gazı oluşumu ise önemli ölçüde azalmakta veya tamamen bitmektedir. Böylelikle, bir yandan depolama alanının faydalı kullanım ömrü artarken, diğer yandan da depolama alanının rehabilitasyonu ve sızıntı suyu arıtım maliyetlerinde düşüş olmaktadır. Bu çalışma kapsamında, bioreaktör depolama yöntemi simüle bioreaktörlerde pilot ölçekli olarak denenmiştir. Sızıntı suyu geri devirli ve havalandırmalı iki simule bioreaktörlerde, atık boyutunun ve karakterizasyonunun atık stabilizasyonunu, sızıntı suyu ve depo gazı kalitesini ne yönde etkilediği incelenmiştir. Bu amaçla, reaktörden biri ham atıkla doldurulurken diğeri aynı atığın 80 mm’lik elekten elenmesiyle elde edilen elek altı atıkla doldurulmuştur. Karışık ham atığın ve elek altı atığın organik madde içeriği yaklaşık olarak % 58 ve % 66 olarak belirlenmiştir. Çalışma sonucunda elde edilen veriler, organik madde içeriğinin artmasının ve atık boyutunun küçülmesinin, sızıntı suyu oluşumunu hızlandırdığı, sızıntı suyu kalitesini iyileştirdiği ve atık stabilizasyonunu hızlandırdığı belirlenmiştir. Anahtar Kelimeler: Evsel katı atık, bioreaktör, depolama alanı, stabilizasyon.Sanitary landfills are widely used fort he disposal of Municipal Solid Waste (MSW) primarily due to their economical and convenient advantages. However leachate and gas generation from landfills may pollute the environment if not properly managed. Landfill designs include soil and/or plastic barriers above and below the waste in an attempt to reduce the infiltration of moisture into the waste mass and thus into the environment. This design method induces anaerobic decomposition of waste. Many of the world's landfills are becoming significant risks to the environment. Over time, anaerobic decomposition of wastes can have negative effects on landfill operations, which actually increase the potential for risks to human health and the environment. In addition, an extended post-closure care period is required to maintain the final cap because the settlement that occurs as organic material in the landfill continues to decompose. In recent years, due to the advance knowledge of landfill behavior and decomposition processes of waste, there has been a strong thrust to upgrade existing landfill technology, as a bioreactor landfill. The bioreactor landfill has been defined as "A sanitary landfill operated for the purpose of transforming and stabilizing the readily and moderately decomposable organic waste constituents control to enhance microbiological processes. The bioreactor landfill significantly increases the extent of waste decomposition, conversion rates and process effectiveness over what would otherwise occur within the landfill. Managing landfills as bioreactors has been suggested as an environmentally alternative and bioreactor landfills offer many environmental and financial benefits including accelerated stabilization of the waste which reduces the long-term potential for groundwater contamination and should allow for shorter post-closure care periods, accelerated methane production which makes recovery most cost-effective and more rapid settlement which creates additional volume for waste disposal during useful operating life. Techniques used to enhance biological degradation of waste, in bioreactor landfills, are shredding, leachate recirculation, aeration, pH adjustment, temperature control and addition of nutrient and sludge. In this study, the effects of waste size and characterization on the waste stabilization and leachate characterization were investigated in two simulated aerated bioreactors landfill. The reactors constructed using metal cylinder with a length of 5.65 m and diameter of 2.5 m. auxiliary equipments consisted of water/leachate recirculation system and air injection system. Both of them were operated with leachate recirculation. One of them (R1) was loaded with raw waste and the other one was loaded with sieved waste having a diameter smaller than 80 mm. The average specific weights of the wastes were 670 kg/m3 in R1 and 1040 kg/m3 in R2. The percentage of organic content is 58% in R1 and 66% in R2. The leachate recirculation rates were 0.42 and 0.21 l/ton waste-day in R1 and R2, respectively. Leachate recirculation volume was determined according to moisture content of waste. Air injection rates were adjusted according to gas measurements. The air injection rates in R1 and R2 were, respectively, 1.819 and 1.565 m3/ton waste-day. Waste stabilization and leachate quality was improved in these recirculation volumes and air injection rates. pH, electrical conductivity, alkalinity, chloride, Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD), ammonium nitrogen (NH4-N), Total Kjedhal Nitrogen (TKN), nitrate (NO3), alkaline and heavy metals (Cd, Cr, Cu, Ni, Pb, Zn, Ca, K, Mg, Na) concentrations in leachate and pH, moisture, carbon / nitrogen (C/N) ration, alkaline and heavy metal (Cd, Cr, Cu, Ni, Pb, Zn, Ca, K, Mg, Na) concentrations in solid waste samples were regularly monitored. Additionally, waste temperatures in reactors were measured daily and settlement was calculated according to height of waste. A decreased trend of the organic load, measured as chemical oxygen demand and biochemical oxygen demand, was observed. Leachate analyses showed that the R1 and R2 could remove above 44% and 87% of chemical oxygen demand and 81% and 94% biochemical oxygen demand from leachate. At the end of study, waste settlement reached 25% and 15% mainly due to decomposition of the organic matter. The average pH value was in the range of in leachate and at about 8 in solid waste samples. The results of this study show that size reduction of MSWs contributed to stabilization of solid waste, increase the treatment characteristics of leachate. Bioreactors operated with leachate recirculation and aeration and loaded with sheared waste was found suitable for waste stabilization and improved leachate characterization. Keywords: Municipal solid waste, bioreactor, landfill, stabilization
Emergency services site selection: The integration of analytic hierarchy process and geographic information systems
Get PDFBu araştırmada itfaiye istasyonlarının yeni yerlerinin belirlenmesi aşamasında gözönüne alınabilecek ölçütler saptanmış, Analitik Hiyerarşi Yöntemi (AHY) kavramından yararlanılarak herbir ölçüt için ağırlıklar belirlenmiş ve belirlenen ölçüt ağırlıklarına dayanarak Coğrafi Bilgi Sistemleri (CBS) ortamında en uygun yer analizi yapılmıştır. Ayrıca oluşturulan modelin duyarlılığını test etmek amacıyla yine CBS ortamında duyarlılık analizleri gerçekleştirilmiştir. Gerçekleştirilen bu çalışmalar ile karar vericilere özellikle itfaiye istasyonları gibi acil durum servislerinin en uygun yerlerinin belirlenmesinde verecekleri kararlarda destek sağlayacak bir sistem üzerine odaklanılmıştır. Çalışmada izlenen adımlar şu şekilde özetlenmektedir: Çözülecek problemin/amacın belirlenmesi; itfaiye istasyonlarının yeni yerlerinin belirlenmesinde etkili olası ölçütlerin belirlenmesi; verilerin elde edilmesi, hazırlanması ve düzenlenerek CBS ortamına aktarılması; parça parça olan veri gruplarının bir çalışma bölgesi oluşturacak şekilde düzenlenmesi ve herbir ölçüte (tabaka) karşılık gelen verilerin raster veri formatında betimlenmesi; raster veri gruplarının sınıflandırılması; Analitik Hiyerarşi Yöntemi (AHY) yardımıyla tercih matrislerinin oluşturulması; iki karar verici grubun görüşlerine dayanarak oluşturulan tercih matrisinden yararlanarak özdeğer ve özvektörlerin hesaplanması; AHY’nin sonuçların sentezlenmesi özelliğinden faydalanarak ilgili herbir ölçüt için önem/ağırlık değerlerinin belirlenmesi; ölçütlere ağırlıklı toplama işlemi uygulanarak sonuç raster verisinin CBS ortamında elde edilmesi; oluşturulan modelin duyarlılığının (CBS) ortamında test edilmesi ve yeni itfaiye istasyon yerlerinin belirlenmesinde karar vericilere destek sağlayan bir sistemin önerilmesi. Anahtar Kelimeler: CBS, analitik hiyerarşi yöntemi, yer seçimi, çok ölçütlü karar verme.In the early 1980s Geographical Information Systems (GIS) software emerged as a new information processing technology offering unique capabilities of automating, managing, and analysing a variety of spatial data. Many applications of GIS developed over the last decade provided information necessary for the decision-making in diverse areas including natural resource management, regional planning, and disaster management. Two perspectives on developing better decision support capabilities of GIS can be identified, one based on analytical problem solving as a centrepiece of Spatial Decision Support Systems (SDSS) and another based on integration of GIS and specialized analytical models. According to first perspective, SDSS should offer modelling, optimization, and simulation functions required to generate, evaluate, recommend, and test the sensitivity or problem solution strategies. These capabilities are essential to solving semi-structured spatial decision-making problems. The second perspective on improving the decision support capabilities focuses on the expansion of GIS descriptive, prescriptive, and predictive capabilities by integrating GIS software with other statistical software and analytical models. According to this view, mapping, query, and spatial modelling functions of GIS can provide data display at different scales, preprocessing, and data input for environmental and statistical models. The general objective of Multi-criteria Decision Making (MCDM) is to assist the decision-maker (DM) in selecting the ?best? alternative from the number of feasible choice-alternatives under the presence of multiple choice criteria and diverse criterion priorities. The problem of multicriterion choice in decision making is the paramount challenge faced by individiuals, public and private corporations. The nature of challenge is two-fold: How to identify choice alternatives satisfying the objectives of parties involved in the decision-making process? How to order the set of feasible choice alternatives to identify the most preferred alternative? The challenge of multicriterion choice can be attributed to many spatial decision-making problems involving search and location/allocation of resources. These problems, often analysed in (GIS), include location/site selection for: service facilities, retail outlets, critical areas for specific resource management, and emergency service locations where are key locations for effective emergency management. In this study, the criteria and its priorities/weights that should be considered for finding optimal locations of fire stations are determined; and multi-criteria site analysis is conducted based on mentioned criteria weights in (GIS) environment. Moreover, in order to test the sensitivity and robustness of the model developed, a sensitivity analysis is performed based on the combination of the criterion weights by using (GIS) capabilities. With these analyses performed, it is focused on the creating the model that supports decision makers in decision-making for finding the optimal locations of fire stations. In this study, these steps are followed: Definition of the problem/objective (determining the optimal locations of fire stations); determining the potential criteria in finding the optimal locations of fire stations; data collection and preparation and transfer to (GIS) environment; creation of raster data sets representing the regionalised criteria; classification of raster data sets; establishment of preference matrix, assigning preference values to the relevant criteria by using the pairwise comparison feature of Analytic Hiyerarchy Process (AHP); determination of criteria weights by calculating eigenvalues and eigenvectors of the preference matrix which evaluated by two decision maker group; determining the criteria priorities/weights values by using the synthesis of priorities and calculating the overall composite weights; calculating the result raster (suitability map for potential fire stations) as a weighted summation of all criteria raster data sets; conducting the sensitivity analyses in (GIS) environment in order to test the sensitiveness and robustness of the model developed; offering a system that supports decision makers in determining the optimal locations of fire stations. The integration of the (AHP) and (GIS) combines decision support methodology with powerful visualisation and analysing capabilities which should considerably facilitate finding optimal locations of fire stations and this process improves the decision making in emergency management. Keywords: GIS, Analytic hierarchy process, site selection, multi-criteria decision making
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