Search

Seismic structural fuses such as buckling restrained braces (BRBs) are highly nonlinear members that need a detailed finite element model (FEM) to represent their actual behavior. On the other hand, making detailed model for the whole building from solid or shell elements to be consistent with the model of BRBs would require expensive computational time and large storage space especially when performing nonlinear time history analysis (NTHA). Therefore, a mixed FEM is developed in this research so that the solid elements are used for the core plate and the restraining system only. The non-yielding segments of the BRBs and the conjoined girders and columns are simulated using beam elements with nonlinear material properties while the effect of large deformations is taken during analysis and this was able to represent plastic hinge formation, plastic rotations and residual displacements in such members. A beam-solid transfer mechanism is developed to properly transfer forces between the non-yielding segments of BRB and the inner solid plate. The core plate is connected to the surrounding restraining system with contact elements to simulate the normal and frictional forces generated upon contact based on the penalty algorithm. This model was validated using the data and the results of an experimental work mentioned in the literature where very good agreement was achieved. Thereafter, a rehabilitation study for the SAC 9-storey building was performed. The results showed how the BRBs work as structural fuses during earthquakes and confirmed the ability of the model to represent inelastic behavior of multi-story BRBFs. [ABSTRACT FROM AUTHOR]

Global warming and anticipated increase in rainfall frequency and magnitude are linked to enhanced rockfall activity worldwide. Arid environments, which currently receive limited amount of annual rainfall, will be particularly subject to frequent and unpredictable rockfall activity that can substantially jeopardize human lives and infrastructures. The main scope of this study is to assess the rockfall hazards in Thawr Mountain and Al-Azyziah district, western Saudi Arabia, using integrated field, geological, climatological and remote sensing datasets and modeling. Our findings indicated that: (1) there are general increasing trends of average annual precipitation and temperature for the period between 2009 and 2019, (2) inspection of multi-temporal satellite images between 2003 and 2017 showed rapid urban expansion, mainly through modification of hillslopes for urban development, which is expected to pose critical consequences on slope instability, (3) field investigations attributed rockfall activity to weathered exfoliated granodiorite hillslopes with abundant tension cracks and steep slopes, (4) slope degrees reached 79° with a general slope direction toward the urbanized areas, and (5) the rockfall motion was simulated along six profiles with dynamic urban areas along the termination of each profile, which showed that several blocks along the six profiles can reach the profile termination with medium intensity rockfall activity and kinetic energy ranges between 50 and 80 kj. The reported rockfall motion can threaten lives, houses and infrastructures. Therefore, protective precautions were suggested to prevent and mitigate the impact of rockfall activity along the studied profiles and similar areas in the mountainous western Arabian Peninsula. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) characterized by high electrical conductivity and thermal stability can be considered as a single monomolecular graphite layer, containing numerous functional oxygen groups such as epoxide, carbonyl, carboxyl and hydroxyl groups. Therefore, in this work, we have come to produce high quantities of GO sheets by innovative, simple and hydrazine-free methods based on rice straw, using catalytic acid spray method (CAS) in the presence of cobalt silicate nanoparticle as a catalyst. The structure of graphene oxide was characterized by FTIR, Raman, HR-TEM and DLS. FTIR shows that GO comprises some efficient hydroxyl (OH), epoxy (cyclic ether), carboxyl and carbonyl groups. XRD shows that the interlayer spacing of GO prepared by our techniques is higher to some extent than the interlayer spacing of other GO produced by another processes. We can say that, GO sheets can be produced for various applications, in large quantities, high efficiency and low cost, by adjusting the parameters such as acid strength or catalytic doses used in the CAS method. Thereby, we can overcome the weak inter-bond between the GO sheets without cracking them. [ABSTRACT FROM AUTHOR]

Modular exponentiation is a fundamental and most time-consuming operation in several public-key cryptosystems such as the RSA cryptosystem. In this paper, we propose two new parallel algorithms. The first one is a fast parallel algorithm to multiply n numbers of a large number of bits. Then we use it to design a fast parallel algorithm for the modular exponentiation. We implement the parallel modular exponentiation algorithm on Google cloud system using a machine with 32 processors. We measured the performance of the proposed algorithm on data size from $$2^{12}$$ to $$2^{20}$$ bits. The results show that our work has a fast running time and more scalable than previous works. [ABSTRACT FROM AUTHOR]

The transparent amorphous carbon thin films (ACTF) were prepared through a batch acid spraying technique in the presence of cobalt silicate as a catalyst at low temperature between 30 and 45 $$^{\circ }\hbox {C}$$ . Hence, the catalyst was prepared using silica gel as a basic matrix and supporting material to produce ACTF. The produced active carbon was characterized using XRD, FTIR, and Raman spectrum. The high-resolution transmission electron microscope (HR-TEM) and thermogravimetric analysis were used to analyze the surface morphology and thermal stability of cellulose and ACTF, whereas the surface area was calculated using the standard iodine method. The results of Raman spectroscopy and TEM show the realization of ACTF suspension with highest constitutional order and the lowest number of layers with confirming of the succeed preparation of thin ACTF layers in thickness and average size of 1 and 100 mm, respectively. In addition, under these conditions, the activated carbons' iodine value is 721.64 mg/g, and the yield ratio is 85.71 %. [ABSTRACT FROM AUTHOR]

Air pollution is one of the most environmentally harmful to the human health and the climate change. The present study is aimed to investigate the effectiveness and capability of novel composite adsorbents prepared from modification of activated carbons (ACs) in the removal of air pollutants. The effect of both triethoxysilane propylamine (TEPSA) and carbon nanotube (CNT) on the adsorption properties of AC (TEPSA/CNT/AC); in addition, silica gel prepared from TEPSA to form silica nanoparticles (SiNP) along with CNT and AC (SiNP/CNT/AC), was studied. Ammonia gas (NH3) was used in this study as a typical emerging gas air pollutant. The physicochemical characteristics of the prepared ACs samples were analyzed using BET surface area, SEM, EDX, TEM and FTIR. Their results proved considerable changes in the porosity and surface functional groups after modifying AC surface with TEPSA or SiNP and CNT instantly. The adsorption findings showed that the NH3 removal efficiency using the prepared AC samples reached almost 97, 86 and 75% during 90 min at 25 °C for each sample of SiNP/CNT/AC, TESPA/CNT/AC and AC, respectively. Adsorption of NH3 relied mainly on the presence of silica particles and mesopore distributions in CNT rather than large total surface area in AC alone. Thus, the combination of SiNP as silanol and siloxane groups with CNT on AC surface raised significantly the adsorption capacity of NH3 from 194 to 300 mg/g. Conclusively, the SiNP/CNT/AC sample exhibited the best performance among all prepared samples used for the adsorption of NH3 gas from the indoor air. Also, Langmuir and Freundlich models were applied, and the results revealed that Freundlich model fits well the equilibrium adsorption data. [ABSTRACT FROM AUTHOR]