Laboratory Investigation on Physical-Mechanical Characteristics and Microstructure of a Clayey Gypsiferous Soil in the Presence of Chemical Accelerator

Reza Bahrami,Navid Khayat,Ahad Nazarpour 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.9

Gypsiferous soils are considered as problematic soils that cause damage to engineering infrastructures, particularly hydraulic structures. The exposition of gypsiferous soils to the steady flow leads to the dissolution of gypsum particles, significantly changing the soil engineering characteristics. In this paper, by employing physical, chemical, and mechanical experiments, the effect of raw gypsum with various percentages (0%, 3%, 6%, 9%, 12% and 15%) on the geotechnical parameters of a low plasticiy clay was investigated through leaching. Electrical conductivity test and ionic concentration analysis were used to assess the trend of gypsum dissolution. The results showed that leaching and increased gypsum content significantly degraded soil engineering characteristics, such as strength and compressibility. Acidic accelerator (diluted acetic acid) speeded up the chemical reaction rate and, at the same time, affected the geotechnical properties of the soil more than water. Mineralogical and microstructural studies (x-ray diffraction, scanning electron microscopy and energy-dispersive x-ray spectroscopy) were carried out to evaluate the interaction between gypsum and soil particles and verify laboratory test results. The x-ray diffraction patterns indicated the formation of new peaks such as calcium aluminate hydrated (CAH) and calcium silicate hydrated (CSH) and the altered structure of pure soil following the addition of raw gypsum. Scanning electron microscope images confirmed the presence of cementitious compounds and changes in the texture of gypsiferous soil in comparison with pure soil. Energy dispersive x-ray interpretation revealed changes in the chemical composition of soil blended with gypsum. The laboratory test results were corroborated by microstructural analyses.

Harmonics Elimination in a Multilevel Inverter with Unequal DC Sources Using a Genetic Algorithm

Iranaq, Ali Reza Marami,Kouhshahi, Mojtaba Bahrami,Kouhshahi, Mehdi Bahrami,Sharifian, Mohammad Bagher Bannae,Sabahi, Mehran Journal of International Conference on Electrical 2012 Journal of international Conference on Electrical Vol.1 No.1

In this paper, an optimal solution to the harmonic reduction problem in a cascaded multilevel inverter with non-equal DC sources using a genetic algorithm (GA) is presented. Switching angles are generated for different values of modulation index by the proposed algorithm, considering minimum voltage total harmonic distortion (THD) whereas selected harmonics are controlled within the allowable limits at all desired modulation indices including the point of discontinuity. Results are stored as a look-up table to be used to control the inverter for a certain operating point. The computed angles are used in a simulated circuit in Matlab\Simulink to validate the results.

Cyber Kill Chain-Based Taxonomy of Advanced Persistent Threat Actors: Analogy of Tactics, Techniques, and Procedures

Bahrami, Pooneh Nikkhah,Dehghantanha, Ali,Dargahi, Tooska,Parizi, Reza M.,Choo, Kim-Kwang Raymond,Javadi, Hamid H.S. Korea Information Processing Society 2019 Journal of information processing systems Vol.15 No.4

The need for cyber resilience is increasingly important in our technology-dependent society where computing devices and data have been, and will continue to be, the target of cyber-attackers, particularly advanced persistent threat (APT) and nation-state/sponsored actors. APT and nation-state/sponsored actors tend to be more sophisticated, having access to significantly more resources and time to facilitate their attacks, which in most cases are not financially driven (unlike typical cyber-criminals). For example, such threat actors often utilize a broad range of attack vectors, cyber and/or physical, and constantly evolve their attack tactics. Thus, having up-to-date and detailed information of APT's tactics, techniques, and procedures (TTPs) facilitates the design of effective defense strategies as the focus of this paper. Specifically, we posit the importance of taxonomies in categorizing cyber-attacks. Note, however, that existing information about APT attack campaigns is fragmented across practitioner, government (including intelligence/classified), and academic publications, and existing taxonomies generally have a narrow scope (e.g., to a limited number of APT campaigns). Therefore, in this paper, we leverage the Cyber Kill Chain (CKC) model to "decompose" any complex attack and identify the relevant characteristics of such attacks. We then comprehensively analyze more than 40 APT campaigns disclosed before 2018 to build our taxonomy. Such taxonomy can facilitate incident response and cyber threat hunting by aiding in understanding of the potential attacks to organizations as well as which attacks may surface. In addition, the taxonomy can allow national security and intelligence agencies and businesses to share their analysis of ongoing, sensitive APT campaigns without the need to disclose detailed information about the campaigns. It can also notify future security policies and mitigation strategy formulation.

A Vectorial-Wave Method for free and forced vibration analysis of extra thin cylindrical shells with boundary discrete damping

Reza Poultangari,Mansour Nikkhah Bahrami 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.7

The Vectorial-wave method (VWM) is developed to study free and forced vibrations of cylindrical shells in the presence of dampers at supports. In modeling the issue, a circular cylindrical shell is considered with two ended supports, including separate springs and viscous dampers in the possible directions. Accordingly, based on Flügge thin shell theory and by considering the wave vectors going in the opposite direction along with the shell axis, reflection and transmission matrices are determined to satisfy the shell continuity as well as the boundary conditions. The proposed method is verified through comparing its results with the available literature and the numerical results calculated by Finite element method (FEM). Employing VWM, the viscous characteristics of the applied supports on natural frequencies of the shell are investigated. Furthermore, frequency responses of the shell, which are affected by point-load excitation, are obtained. Finally, the results show that several tandem resonance picks can be eliminated via accurate setting of the support damping.

Photoinduced Electron Transfer Reactions of Aryl Benzyl Sulfides Promoted by 2,4,6-Triphenylpyrilium Tetrafluoroborate (TP+BF4-)

Hamid Reza Memarian*,Iraj Mohammadpoor-Baltork,Kiumars Bahrami 대한화학회 2006 Bulletin of the Korean Chemical Society Vol.27 No.1

Evaluation of the cell viability and antimicrobial effects of orthodontic bands coated with silver or zinc oxide nanoparticles: An in vitro study

Rashin Bahrami,Maryam Pourhajibagher,Alireza Badiei,Reza Masaeli,Behrad Tanbakuchi 대한치과교정학회 2023 대한치과교정학회지 Vol.53 No.1

Objective: We aimed to evaluate the cell viability and antimicrobial effects of orthodontic bands coated with silver or zinc oxide nanoparticles (nano-Ag and nano-ZnO, respectively). Methods: In this experimental study, 30 orthodontic bands were divided into three groups (n = 10 each): control (uncoated band), Ag (silver-coated band), and ZnO (zinc oxide-coated band). The electrostatic spray-assisted vapor deposition method was used to coat orthodontic bands with nano-Ag or nano-ZnO. The biofilm inhibition test was used to assess the antimicrobial effectiveness of nano-Ag and nano-ZnO against Streptococcus mutans, Lactobacillus acidophilus, and Candida albicans. Biocompatibility tests were conducted using the 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay. The groups were compared using one-way analysis of variance with a post-hoc test. Results: The Ag group showed a significantly higher reduction in the number of L. acidophilus, C. albicans, and S. mutans colonies than the ZnO group (p = 0.015, 0.003, and 0.005, respectively). Compared with the control group, the Ag group showed a 2-log10 reduction in all the microorganisms' replication ability, but only S. mutants showed a 2-log10 reduction in replication ability in the ZnO group. The lowest mean cell viability was observed in the Ag group, but the difference between the groups was insignificant (p > 0.05). Conclusions: Coating orthodontic bands with nano-ZnO or nano-Ag induced antimicrobial effects against oral pathogens. Among the nanoparticles, nano-Ag showed the best antimicrobial activity and nano-ZnO showed the highest biocompatibility.

Identification of pore types and pore facies for evaluating the diagenetic performance on reservoir quality: a case study from the Asmari Formation in Ramin Oil Field, SW Iran

Farshad Bahrami,Reza Moussavi-Harami,Mohammad Khanehbad,Mohamad Hosein Mahmudy Gharaie,Rahmatollah Sadeghi 한국지질과학협의회 2017 Geosciences Journal Vol.21 No.4

The purpose of this study is to identify the pore types and distinguish the pore facies based on the diagenetic performance. The petrographic examination of 230 thin sections lead to the identification of a variety of primary and secondary porosities and show that the vuggy, moldic and intercrystalline pores have more frequency than the intraparticle, interparticle and fenestral pores. The plot of data obtained from thin sections on the ternary porosity graph used for determining the pore facies and their diagenetic trends and led to the identification of6 pore facies including depositional (PF1), moldic (PF4), and vuggy (PF6) pore facies, and also mixture pore facies PF2 (mixture of PF1 and PF4), PF3 (mixture of PF1 and PF6) and PF5 (mixture of PF4 and PF6). The comparison of petrography results with the well logs, core permeability and the calculated RQI and FZI values show that the pore facies which have touching pores, especially PF6 and PF1, have played the most important role in improving the quality of the reservoir, especially in the upper part of the studied zone. Also the pore facies which have separate pores, especially PF4, have the most influence in the reduction of reservoir quality relative to other pore facies, especially in the lower part of the studied zone. Most of the pores identified in the studied zone are the secondary porosity and diagenetic in origin. This demonstrates that the reservoir characteristics in the studied zone have been strongly modified by diagenetic overprinting. The most important diagenetic processes affecting the pore systems of the Asmari reservoir are cementation, selective and massive dissolution and dolomitization. Massive dissolution plays the most active role in the formation of touching vugs as well as enhancement of reservoir quality. Cementation and fabric selective dolomitization play the most active role in decrease of the reservoir quality.

Photoinduced Electron Transfer Reactions of Aryl Benzyl Sulfides Promoted by 2,4,6-Triphenylpyrilium Tetrafluoroborate (TP⁺BF₄^-)

Memarian, Hamid Reza,Ira, Mohammadpoor Baltork,Bahrami, Kiumars Korean Chemical Society 2006 Bulletin of the Korean Chemical Society Vol.27 No.1

Photocatalytic electron transfer reactions of aryl benzyl sulfides using 2,4,6 triphenylpyrilium tetrafluoroborate ($TP^+BF_4^-$) resulted in the oxidation of these sulfides to the corresponding sulfoxides and also in most cases in the C-S bond cleavage of them along with formation of aromatic aldehydes. In these reactions, the formation of sulfide radical cation has been proposed, which undergoes either oxidation to the corresponding sulfoxide or C-S bond cleavage to the formation of aromatic aldehydes. The further oxidation of sulfoxides to sulfones has not been observed. The influence of substrate structures on the reaction pathways as well as the role of $O_2$ in this respect is discussed.

Effect of the circle tunnel on induced force distribution around underground rectangular gallery using theoretical approach, experimental test and particle flow code simulation

Vahab Sarfarazi,Reza Bahrami,Shadman Mohammadi Bolbanabad,Fariborz Matinpoor 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.84 No.5

In this study, the effect of circle tunnel on the force distribution around underground rectangular gallery was investigated using theoretical approach, experimental test and Particle flow code simulation (PFC). Gypsum model with dimension of 1500×1500 mm was built. Tensile strength of material was 1 MPa. Dimension of central gallery was 100 mm×200 mm and diameter of adjacent tunnel in its right side was 20 mm, 40 mm and 60 mm. Horizontal distance between tunnel wall and gallery edge were 25, 50, 75, 100 and 125 mm. using beam theory, the effect of tunnel diameter and distance between tunnel and gallery on the induced force around gallery was analyzed. In the laboratory test, the rate of loading displacement was set to 0.05 millimeter per minute. Also sensitivity analysis has been done. Using PFC2D, interaction between tunnel and gallery was simulated and its results were compared with experimental and theoretical analysis. The results show that the tensile force concentration has maximum value in center of the rectangular space. The tensile force concentration at the right side of the axisymmetric line of gallery has more than its value in the left side of the galleries axisymmetric line. The tensile force concentration was decreased by increasing the distance between tunnel and rectangular space. In whole of the configurations, the angles of micro cracks fluctuated between 75 and 105 degrees, which mean that the variations of tunnel situation have not any influence on the fracture angle.

Cyber Kill Chain-Based Taxonomy of Advanced Persistent Threat Actors: Analogy of Tactics, Techniques, and Procedures

Pooneh Nikkhah Bahrami,Ali Dehghantanha,Tooska Dargahi,Reza M. Parizi,Kim-Kwang Raymond Choo,Hamid H. S. Javadi 한국정보처리학회 2019 Journal of information processing systems Vol.15 No.4

The need for cyber resilience is increasingly important in our technology-dependent society where computingdevices and data have been, and will continue to be, the target of cyber-attackers, particularly advancedpersistent threat (APT) and nation-state/sponsored actors. APT and nation-state/sponsored actors tend to bemore sophisticated, having access to significantly more resources and time to facilitate their attacks, which inmost cases are not financially driven (unlike typical cyber-criminals). For example, such threat actors oftenutilize a broad range of attack vectors, cyber and/or physical, and constantly evolve their attack tactics. Thus,having up-to-date and detailed information of APT’s tactics, techniques, and procedures (TTPs) facilitates thedesign of effective defense strategies as the focus of this paper. Specifically, we posit the importance oftaxonomies in categorizing cyber-attacks. Note, however, that existing information about APT attackcampaigns is fragmented across practitioner, government (including intelligence/classified), and academicpublications, and existing taxonomies generally have a narrow scope (e.g., to a limited number of APTcampaigns). Therefore, in this paper, we leverage the Cyber Kill Chain (CKC) model to “decompose” anycomplex attack and identify the relevant characteristics of such attacks. We then comprehensively analyze morethan 40 APT campaigns disclosed before 2018 to build our taxonomy. Such taxonomy can facilitate incidentresponse and cyber threat hunting by aiding in understanding of the potential attacks to organizations as wellas which attacks may surface. In addition, the taxonomy can allow national security and intelligence agenciesand businesses to share their analysis of ongoing, sensitive APT campaigns without the need to disclose detailedinformation about the campaigns. It can also notify future security policies and mitigation strategy formulation.