Sharif Digital Repository

Let D be an F-central division algebra of index n. In this thesis a criterion for the triviality of the group G(D) = D^*/Nrd_(D/F) (D^*)D^' is presented and thus generalizing various related results published recently. To be more precise, it is shown that G(D) = 1 if and only if SK〗_1 (D) = 1 and (F^* )^2=(F^* )^2n. By using this, the role of some particular subgroups of D* in the algebraic structure of D is investigated. In this direction, it is proved that a division algebra D of prime index is a symbol algebra if and only if D* contains a non-abelian nilpotent subgroup  

The goal of this research is the probabilistic estimation of time and cost of the process of seismic retrofitting of structural elements of buildings. In the past, many models have been proposed for estimating the cost of retrofitting buildings, especially masonry buildings. Most of these models have been developed using data from a limited number of retrofitting projects and employing methods such as fitting or regression. A review of the technical literature shows that previous research has not modeled the execution of building retrofitting operations and their complexities, which significantly affect the cost of these projects. Furthermore, the duration of building retrofitting operations... 

The Cu2ZnSnS4 (CZTS) quaternary compound, with suitable optical and electrical properties, is one of the most interesting materials for absorber layer of thin film solar cell. Since all constituents of CZTS, are abundant in earth’s crust and non-toxic, it is a proper replacement for the materials like CdTe and CuInSe2. The CZTS pellet was synthesized by the solid-state reaction and deposited on soda lime glass substrates by pulsed laser deposition (PLD) method. PLD technique has the advantages of offering stoichiometric preservation during the materials transformation from target to substrate and good crystallinity due to the highly energetic species. CZTS has was deposited in order to... 

The main aim of this study is to propose a new structure of compression surfaces of a supersonic inlet in order to improve target performance parameter i.e. total pressure recovery ratio. This idea resulted in developing a new type of supersonic inlet, utilizing four ramps and a cone as compression surfaces simultaneously.A prototype of this type of inlet has been designed for Mach 3 and its performance has been studied via numerical simulation in design point and off design conditions. Eventually the new inlet compared to experimental performance survey data from two cases of two-cone inlets and also analytical calculations of ideal performance of some types of supersonic inlets. Results of... 

Wireless Sensor Networks (WSNs) are prone to faults due to battery depletion of nodes, where a node failure can disturb routing, as it plays a key role in transferring sensed data to the end users. A WSN may be partitioned into groups of nodes called clusters; for every cluster, there is a node, called Cluster Head (CH) that is responsible for collecting and transferring data from all nodes in that cluster. This means that the CH is a single point of failure; i.e., once a CH fails, the whole cluster will fail, which leads to inability of its members for transferring data outside the cluster. This thesis presents a Fault-Tolerant and Energy-Aware algorithm (FTEA), which prolongs the lifetime... 

Physical and chemical properties of tungsten oxide thin films change reversibly while exposure to hydrogen gas. This property is called gasochromic. To enhance optical properties of such films, nanostructured, amorphous and porous thin films of (WO3)1-x(MeO)x (MeO= TiO2, MoO3, NiO; x=0.09, 0.17, 0.23, 0.29, 0.33) were fabricated by Pulsed Laser Deposition. Molar percentage of Me/W (Me= Ti, Mo and Ni) was changed in films with respect to targets; for Ti and Ni always a reduction, but for Mo an enhancement for low percentages was observed. The reason is the existence of thermal ablation mechanism during deposition, in the other word is different vapor pressure effect. An increment in x for... 

The Cu2ZnSnS(e)4 (CZTS(e)) quaternary and Cu2SnS3 (CTS) ternary componds with suitable optical and electrical properties have been considered as an emerging semiconductors for fabrication of thin-fim solar cells. So far, two technologies based on CdTe and CuInGaS(e)2 absorbers have achived efficiencies above 20%. However, these compounds contain toxic element Cd and rare elements such as In and Ga which, limited the development of these solar cells.In this research a 3-stage method was used for fabrication of CZTS(e) thin Films. In the first stage, CTS layers were deposited by spray pyrolysis method, in the second one, ZnS layers were also deposited on CTS layers by spray pyrolysis method... 

In this study a new SPH model for solving free surface and fluid-fluid interaction problems is presented. The numerical model is capable of simulating two dimensional hydraulic problems with arbitrary boundary and initial conditions and large number of particles. It has the ability to model multi-fluids domain with different densities and viscosities. Several corrections are implemented in SPH formulation such as treatment of free surface and correction of viscous term in order to conserve the angular momentum. Several examples are conducted in fluid-fluid domains to measure the capability of model in this area of study. This new model use Incompressible SPH method for more accurate... 

Given a divisible finite field extension KjF, the structure of Br(F), the Brauer group of F, is investigated. It is shown that, if F is indivisible, then Br(F) = Z2, which generalizes the Frobenius Theorem. As a consequence, when F is indivisible, the class of all finite dimensional non-commutative F-central division algebras D having radicable multiplicative groups D is determined. In fact, it is proved that the following statements are equivalent: (1) D is radicable, (2) D contains a divisible subfield KjF, and (3) D is the ordinary quaternion division algebra and F(p 1) is divisible  

In this research, a new approach for TWS (Track While Scan) systems is introduced. Conventional TWS systems usually use target’s position (in Cartesian or polar coordinate systems), its velocity, and sometimes its acceleration (in main directions of coordinate system which is being used) as the elements of target’s state vector but the suggested algorithms use target’s velocity, course of motion and their rates of change as main tracking quantities and target’s position will be calculated after updating its velocity and course of motion. Hough transform is used as a powerful tool in detecting patterns which are identified with finite parameters (like lines, circles, ellipses, etc) to... 

The problem of guarding orthogonal art galleries with sliding cameras is a special case of the well-known art gallery problem when the goal is to minimize the number of guards. Each guard is considered as a point, which can guard all points that are in its visibility area. In the sliding camera model, each guard is specified by an orthogonal line segment which is completely inside the polygon. The visibility area of each sliding camera is defined by its line segment.Inspired by advancements in wireless technologies and the need to offer wireless ser- vices to clients, a new variant of the problems for covering the regions has been studied. In this problem, a guard is modeled as an... 

Copper-based semiconductors have received a great deal of attention due to their high absorption coefficient, direct and adjustable energy gap with stoichiometry, low frequency and toxicity. Multicomponent nanocrystals such as CuInS2, Cu (In, Ga) (S, Se) 2, Cu2ZnSnS4 and Cu2SnS3 (CTS) have been successfully synthesized by colloidal synthesis and have shown application potentials such as energy conversion, photocatalyst, thermoelectric and biomedical. Among these, the CTS ternary semiconductor with p-type conduction is one of the most well-known compounds of group I-IV-VI, which consists of abundant and non-toxic elements. In this research, thin-film solar cells with FTO / TiO2 / In2S3 / CdS... 

Our main purpose is introducing essential dimension and investigating properties of this concept and definition of it on different algebraic objects and proving some theories about it. In the beginning we define the concept of essential dimension on the extension fields which indeed it is expressing complexity of extension on the background field.Then with the meaning of noetherian extension which we will introduce it in the chapter three, we generalize the concept of essential dimension to finite groups. At last we investigate the connection between the essential dimension with generic polynomials and one of our important results is finding upper bounds for essential dimension of finite... 

If L is a finite-dimensional Lie algebra over the field F then the universal enveloping algebra U(L) can be embedded in a division ring D. In particular, if L is a solvable p-algebra, there is a decomposition D=KR where K and R are maximal subfields of D, K is Galois extension of the center Z of D and R is a purely inseparable extension of Z with R^p⊆Z. The present thesis is concerned with the compared structures of maximal subfields in a division D and in the division ring of rational functions D(X). We prove that maximal subfields of D(X) “generically” specialize to maximal subfields of D, and properties such as being Galois or purely inseparable over the centre also carry over... 

In this Mater thesis, we o?er a general Prime Ideal Principle for proving that certain ideals in a commutative ring are prime. This leads to a direct and uniformtreatment of a number of standard results on prime ideals in commutative algebra,due to Krull, Cohen, Kaplansky, Herstein, Isaacs, McAdam, D.D. Anderson, andothers. More signi?cantly, the simple nature of this Prime Ideal Principle enablesus to generate a large number of hitherto unknown results of the “maximal impliesprime” variety. The key notions used in our uniform approach to such prime idealproblems are those of Oka families and Ako families of ideals in a commutative ring.In chapter 2, we amplify this study by developing... 

In this thesis we investigate identities on maximal subgroups of developed by D. Kiani and M. Mahdavi-Hezavehi . Let be a division ring with centre and a maximal subgroup of ( ) . Several group identities on M and polynomial identities on the F-linear hull where is algebraic over F are studied. We show that if is a PI-algebra, then . When is non-commutative and is infinite, we show that if satisfies a group identity and is algebraic over , then we have either where is a field and , or is absolutely irreducible. Finally for a finite-dimensional division algebra and a subnormal subgroup of we show that if is a maximal subgroup of that satisfies a group identity,... 

In this thesis we study the structure of locally solvable, solvable, locally nilpotent, and nilpotent maximal subgroups of skew linear groups. In [5] it has been conjectured that if D is a division ring and M a nilpotent maximal subgroup of , then D is commutative. In connection with this conjecture we show that if M a nilpotent maximal subgroup of , then M is an abelian group. Also we show that is a solvable maximal subgroup of real quaternions and so give a counterexample to Conjecture 3 of [5], which states that if D is a division ring and M a solvable maximal subgroup of , then D is commutative. Also we completely determine the structure of division rings with a non-abelian... 

Defining the structure of maps using local features is among the popular fields of study in mathematics. Therefore determining the structure of maps on rings which behave like derivations at idempotent-product elements has been getting attention recently. This subject is useful for examining the structure of rings and algebraic operators in both algebra and analysis as well. Suppose that R is a ring, d : R ! R is an additive map, z 2 R and d meets the condition below: 8a; b 2 R : d(ab) = ad(b) + d(a)b Therefore d is called a derivation on R. If for every a; b 2 R where ab = z, d(ab) = ad(b) + d(a)b then d behaves like a derivation at idempotent-product elements of ab = z. The main challenge... 

This thesis is a survey of results of studies and researches in theory of Division rings and multiplicative groups of division rings and relations between group strcture and algebraic structure of division rings.in this case,we emphesized on study of finitely generated,maximal,nilpotent and soluble subgroups of division rings.we also,study the Valuation theory on division rings and Reduced K-theory of division rings and relations between these theories and group structure of division rings,morever,those which is finite dimensional over their center as vector spaces.at the end,we shortly,study divisible division rings and radicable division rings