Generalized matrix functions, irreducibility and equality

Mohammad Hossein Jafari,Ali Reza Madadi 대한수학회 2014 대한수학회보 Vol.51 No.6

Let G ≤ Sn and Χ be any nonzero complex valued function on G. We first study the irreducibility of the generalized matrix polyno- mial dGΧ (X), where X = (xij ) is an n-by-n matrix whose entries are n2 commuting independent indeterminates over C. In particular, we show that if Χ is an irreducible character of G, then dGΧ (X) is an irreducible polynomial, where either G = Sn or G = An and n 6= 2. We then give a necessary and sufficient condition for the equality of two generalized matrix functions on the set of the so-called Χ-singular (Χ-nonsingular) matrices.

Participation of the Women Covered by Family Physicians in Breast Cancer Screening Program in Kerman, Iran

Jafari, Mohammad,Nakhaee, Nouzar,Goudarzi, Reza,Zehtab, Nooshin,Barouni, Mohsen Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.11

Background: Mammography screening is a method for reducing breast cancer mortality in women over 40 years old. A participation rate of at least 70% is a prerequisite for screening programs. This study aimed at determining the participation rate of women in breast cancer screening in Iran. Materials and Methods: The study population in this prospective research consisted of 35 to 69 years old women in the villages and towns Kerman District, in 2013. The data were collected by a well-validated risk assessment questionnaire. The questionnaires were completed with the help of health workers and technicians in the health centers, who were trained on breast cancer screening program. Results: As a whole, 19,651 women were invited to complete the questionnaire, of whom 15,794 women (80.37%) completed it. In the urban region, of 3150 eligible women 2728 women (86.60%) participated in the study. The acceptance rates for mammography in rural and urban regions were 34.95% and 8.75%, respectively. Conclusions: Finally, 3.8% and 16.34% of 35 to 69 years old women in the urban regions were mammographed, respectively. Conclusion: The low participation of eligible women in breast cancer screening program alerts us against including the program in the health insurance package.

Ant lion optimizer for optimization of finite perforated metallic plate

Mohammad H. Bayati Chaleshtari,Mohammad Jafari 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.69 No.6

Minimizing the stress concentration around hypotrochoid hole in finite metallic plates under in-plane loading is an important consideration in engineering design. In the analysis of finite metallic plate, the effective factors on stress distribution around holes include curvature radius of the corner of the hole, hole orientation, plate’s aspect ratio, and hole size. This paper aims to investigate the impact of these factors on stress analysis of finite metallic plate with central hypotrochoid hole. To obtain the lowest value of stress around a hypotrochoid hole, a swarm intelligence optimization method named ant lion optimizer is used. In this study, with the hypothesis of plane stress circumstances, analytical solution of Muskhelishvili’s complex variable method and conformal mapping is employed. The plate is taken into account to be finite, isotropic and linearly elastic. By applying suitable boundary conditions and least square boundary collocation technique, undefined coefficients of stress function are found. The results revealed that by choosing the above-mentioned factor correctly, the lowest value of stress would be obtained around the hole allowing to an increment in load-bearing capacity of the structure.

Determination of optimal parameters for perforated plates with quasi-triangular cutout by PSO

Mohammad Jafari,Seyed A. Mahmodzade Hoseyni,Mohammad H. Bayati Chaleshtari 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.60 No.5

This study tries to examine the effect of different parameters on stress analysis of infinite plates with central quasi-triangular cutout using particle swarm optimization (PSO) algorithm and also an attempt has been made to introduce general optimum parameters in order to achieve the minimum amount of stress concentration around this type of cutout on isotropic and orthotropic plates. Basis of the presented method is expansion of analytical method conducted by Lekhnitskii for circular and elliptical cutouts. Design variables in this study include fiber angle, load angle, curvature radius of the corner of the cutout, rotation angle of the cutout and at last material of the plate. Also, diagrams of convergence and duration time of the desired problem are compared with Simulated Annealing algorithm. Conducted comparison is indicative of appropriateness of this method in optimization of the plates. Finite element numerical solution is employed to examine the results of present analytical solution. Overlap of the results of the two methods confirms the validity of the presented solution. Results show that by selecting the aforementioned parameters properly, less amounts of stress can be achieved around the cutout leading to an increase in load-bearing capacity of the structure.

ON THE NUMBER OF CYCLIC SUBGROUPS OF A FINITE GROUP

Jafari, Mohammad Hossein,Madadi, Ali Reza Korean Mathematical Society 2017 대한수학회보 Vol.54 No.6

Let G be a finite group and m a divisor of ${\mid}G{\mid}$. We prove that G has at least ${\tau}(m)$ cyclic subgroups whose orders divide m, where ${\tau}(m)$ is the number of divisors of m.

Variation of Contact Angles in Brine/CO₂/Mica System considering Short-Term Geological CO₂ Sequestration Condition

Jafari, Mohammad,Jung, Jongwon Hindawi Limited 2018 Geofluids Vol.2018 No.-

<P>Geological CO2 sequestration has been proposed as an effective solution to mitigate excessive human-emitted CO2 in atmosphere. Knowledge of immiscible two-phase flow of CO2-water/brine is necessary to evaluate the efficiency and safety of geological storage sites. Among forces dominating fluid flow, capillary pressure is highly important because of high uncertainty in measurement due to ambiguous wettability behavior of geomaterials. In particular, time-dependent wettability of geomaterials is of interest for predicting short-term performance of the storage site. After injection of CO2 into an aquifer, both the CO2 and water/brine in rocks pores are unsaturated and tend to dissolve into each other. Present study investigates the variation of contact angle on mica sheet using a captive bubble method at a wide range of pressures and salinities under unsaturated condition. Our results showed a general increase of contact angle with time. Comparison of unsaturated contact angle with previous results in the literature showed a wide span of wettability behavior, ranging from receding to advancing contact angle values reported in the literature. The observed decrease in wettability by time due to heterogeneity and pinning effect of triple line can jeopardize the safety of geological carbon sequestration projects in short-term after injection of CO2.</P>

GENERALIZED MATRIX FUNCTIONS, IRREDUCIBILITY AND EQUALITY

Jafari, Mohammad Hossein,Madadi, Ali Reza Korean Mathematical Society 2014 대한수학회보 Vol.51 No.6

Let $G{\leq}S_n$ and ${\chi}$ be any nonzero complex valued function on G. We first study the irreducibility of the generalized matrix polynomial $d^G_{\chi}(X)$, where $X=(x_{ij})$ is an n-by-n matrix whose entries are $n^2$ commuting independent indeterminates over $\mathbb{C}$. In particular, we show that if $\mathcal{X}$ is an irreducible character of G, then $d^G_{\chi}(X)$ is an irreducible polynomial, where either $G=S_n$ or $G=A_n$ and $n{\neq}2$. We then give a necessary and sufficient condition for the equality of two generalized matrix functions on the set of the so-called ${\chi}$-singular (${\chi}$-nonsingular) matrices.

Wind tunnel study of wake-induced aerodynamics of parallel stay-cables and power conductor cables in a yawed flow

Mohammad Jafari,Partha P. Sarkar 한국풍공학회 2020 Wind and Structures, An International Journal (WAS Vol.30 No.6

Wake-induced aerodynamics of yawed circular cylinders with smooth and grooved surfaces in a tandem arrangement was studied. This pair of cylinders represent sections of stay-cables with smooth surfaces and high-voltage power conductors with grooved surfaces that are vulnerable to flow-induced structural failure. The study provides some insight for a better understanding of wake-induced loads and galloping problem of bundled cables. All experiments in this study were conducted using a pair of stationary section models of circular cylinders in a wind tunnel subjected to uniform and smooth flow. The aerodynamic force coefficients and vortex-shedding frequency of the downstream model were extracted from the surface pressure distribution. For measurement, polished aluminum tubes were used as smooth cables; and hollow tubes with a helically grooved surface were used as power conductors. The aerodynamic properties of the downstream model were captured at wind speeds of about 6-23 m/s (Reynolds number of 5×104 to 2.67×105 for smooth cable and 2×104 to 1.01×105 for grooved cable) and yaw angles ranging from 0º to 45º while the upstream model was fixed at the various spacing between the two model cylinders. The results showed that the Strouhal number of yawed cable is less than the non-yawed case at a given Reynolds number, and its value is smaller than the Strouhal number of a single cable. Additionally, compared to the single smooth cable, it was observed that there was a reduction of drag coefficient of the downstream model, but no change in a drag coefficient of the downstream grooved case in the range of Reynolds number in this study.

On the number of cyclic subgroups of a finite group

Mohammad Hossein Jafari,Ali Reza Madadi 대한수학회 2017 대한수학회보 Vol.54 No.6

Let $G$ be a finite group and $m$ a divisor of $|G|.$ We prove that $G$ has at least $\tau(m)$ cyclic subgroups whose orders divide $m$, where $\tau(m)$ is the number of divisors of $m.$

Experimental evaluation of splicing of longitudinal bars with forging welding in flexural reinforced concrete beams

Sharbatdar, Mohammad K.,Jafari, Omid Mohammadi,Karimi, Mohammad S. Techno-Press 2018 Advances in concrete construction Vol.6 No.5

In this paper the application of forging process as benefit technique in Reinforced Concrete (RC) beam bars and comparison to lap splices was experimentally investigated with four concrete beam specimens with same dimensions and reinforcement details. The reference specimen was with no splices and the other three beams were with different splices (100% forging in the middle, 50% forging, and 100% lap splices in the middle). Beams were tested with the four points load system. Experimental test results indicated that using forging process as new bar splicing method can have high effects on increasing ductility and energy dissipation of concrete structures. It also proved that this method increased the flexural rigidity, energy absorption, and ductility of the RC beams. And also this research results showed that the flexural capacity and ductility of the beam with 50% forging were respectively increased up to 10% and 75% comparing to that of reference specimen, but the energy absorption of this beams was decreased up to 27%. The ductility of beam with 50% forging was increased up to 25% comparing the ductility of beam with 100% forging.