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      • KCI등재

        An optimized rational fraction polynomial approach for modal parameters estimation from FRF measurements

        Omar Omar,Nejah Tounsi,Eu-Gene Ng,M. A. Elbestawi 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.3

        This paper presents an Optimized Rational Fraction Polynomial (ORFP) approach for modal parameters estimation from the measurements of the Frequency Response Function (FRF). Although this approach is based on the Rational Fraction Polynomial (RFP) technique described in [1], it suggests the use of a constrained optimization scheme rather than the Forsythe method to overcome the shortcomings of the Forsythe method. The latter are the estimation of modal parameters that do not necessarily describe a stable system and the estimation of fictitious natural frequencies. The formulation of the constrained optimization problem is presented and discussed. The assessment of the performance of the ORFP approach showed that it is better than the RFP approach in terms of its ability to identify modal parameters that ensure a stable system and its flexibility in selecting and setting the natural frequencies of the system. Several illustrative examples are given to demonstrate the robustness of the ORFP approach.

      • Effect of horizontal joints on structural behavior of sustainable self-compacting reinforced concrete beams

        Ibrahim, Omar Mohamed Omar,Heniegal, Ashraf Mohamed,Ibrahim, Khamis Gamal,Agwa, Ibrahim Saad Techno-Press 2020 Advances in concrete construction Vol.10 No.5

        This study investigated the effect of horizontal casting joints on the mechanical properties and structural behavior of sustainable self-compacting reinforced concrete beams (SCRCB). The experimental research consisted of two stages. The first stage used four types of concrete mixtures which were produced to indicate the effects of cement replaced with cement waste at 0%, 5%, 10%, and 15% by weight of cement content on fresh concrete properties of self-compacting concrete (SCC) such as, passing ability, filling ability, and segregation resistance. In addition, mechanical properties such as compressive, tensile, and flexural strength were also studied. The second stage selected the best mixture from the first stage and studied the effect of horizontal casting joints on the structural behavior of sustainable SCRCBs. The effect of horizontal casting joints on the mechanical properties and structural behavior were at the 25%, 50%, 75%, and 100% of sample height. Load deflection, failure mode, and theoretical analysis were studied. Results indicated that the incorporation of replacement with cement waste by 5% to 10% led to economic and environmental advantages, and the results were acceptable for fresh and mechanical properties. The results indicated that delaying the time for casting the second layer and increasing the cement waste in concrete mixtures had a great effect on the mechanical properties of SCC. The ultimate load capacity of horizontal casting joints reinforced concrete beams slightly decreased compared with the control beam. The maximum deflection of casting joint beams with 75% of samples height is similar with the control beam. The experimental results of reinforced concrete beams were substantially acceptable with the theoretical results. The failure modes obtained the best forced casting joint on the structural behavior at 50% height of casting in the beam.

      • Combined effect of lightweight fine aggregate and micro rubber ash on the properties of cement mortar

        Ibrahim, Omar Mohamed Omar,Tayeh, Bassam A. Techno-Press 2020 Advances in concrete construction Vol.10 No.6

        Exterior walls in buildings are exposed to various forms of thermal loads, which depend on the positions of walls. Therefore, one of the efficient methods for improving the energy competence of buildings is improving the thermal properties of insulation plaster mortar. In this study, lightweight fine aggregate (LWFA) and micro rubber ash (MRA) from recycled tires were used as partial replacements for sand. The flow ability, unit weight, compressive strength, tensile strength, thermal conductivity (K-value), drying shrinkage and microstructure scan of lightweight rubberized mortar (LWRM) were investigated. Ten mixtures of LWRM were prepared as follows: traditional cement mortar (control mixture); three mixes with different percentages of LWFA (25%, 50% and 75%); three mixes with different percentages of MRA (2.5%, 5% and 7.5%); and three mixes consisting both types with determined ratios (25% LWFA+5% MRA, 50% LWFA+5% MRA and 75% LWFA+5% MRA). The flow ability of the mortars was 22±2 cm, and LWRM contained LWFA and MRA. The compressive and tensile strength decreased by approximately 64% and 57%, respectively, when 75% LWFA was used compared with those when the control mix was used. The compressive and tensile strength decreased when 5% MRA was used. By contrast, mixes with determined ratios of LWFA and MRA affected reduced unit weight, K-value and dry shrinkage.

      • KCI등재

        Valorization of Dredged Sediments as a Component of Vibrated Concrete

        Omar Safer,Nadia Belas,Omar Belaribi,Khalil Belguesmia,Nasr-Eddine Bouhamou,Abdelkader Mebrouki 한국콘크리트학회 2018 International Journal of Concrete Structures and M Vol.12 No.4

        Hydraulic facilities are subjected to significant siltation which, in a very short period of time, can render them unusable. In Algeria, the silting-up of a great number of dams, built for drinking water needs and for irrigation, implies the necessity and urgency to take action. Therefore, the maintenance work, which leads to dredging the deposited silt, constitutes an unbearable obligation for the preservation of the environment. Chorfa dam (western Algeria) may be mentioned as a concrete example. This study is part of a long research whose objective is to contribute to the valorization and the optimization of the formulations economically that are easy to implement and which enable to use the dredged materials in the formulation of ordinary concretes by partial substitution to cement (10, 20 and 30%) of dredged sediments, after calcination at 750℃ to make them active. Tests were carried out on concrete that was vibrated in the fresh state (setting time) and hardened state (compressive strengths and durability of concrete exposed to sulfuric acid attack) in order to determine their characteristics. The results obtained confirmed the possibility to develop concretes containing calcined silt, with proportions up to 30%, and which can meet the economic, ecological and technological objectives.

      • KCI등재

        Histologically confirmed upper gastrointestinal Crohn’s disease: is it rare or are we just not searching hard enough?

        ( Omar Ibrahim Saadah ),( Kholoud Bakur Fallatah ),( Cedric Baumann ),( Abdulrahman Ahmed Elbaradie ),( Fatimah Talat Howladar ),( Motaz Tariq Daiwali ),( Omar Hamad Alshuaibi ),( Majid Abdulaziz Alsa 대한장연구학회 2020 Intestinal Research Vol.18 No.2

        Background/Aims: Crohn’s disease (CD) may involve the upper parts of the gastrointestinal (GI) tract including the esophagus, stomach, and duodenum. Clinical features of upper GI CD (UGICD) are not well characterized in the Gulf region. We therefore aimed to assess the prevalence and clinical characteristics of patients diagnosed with UGICD. Methods: We performed a retrospective analysis of all patients diagnosed with CD who underwent upper GI endoscopy between 2012 and 2017 at King Abdulaziz University Hospital, irrespective of age. Patients who had endoscopy of the upper GI tract at baseline and had histologically confirmed UGICD were included. Data on patients’ demographics, clinical characteristics, extraintestinal manifestations and complications were reviewed. Results: We identified 78 CD patients who underwent upper GI endoscopy from our medical records. The mean age was 17.2±8.7 years and 55.1% were males. Of the total, 19 out of 78 patients (24.4%) had histologically confirmed UGICD (3 esophageal, 16 gastric, and 9 duodenal), of which 52.6% were symptomatic. Disease distribution was ileal in 57.8%, colonic in 21.1% and ileo-colonic in 21.1%. A non-stricturing and non-penetrating phenotype was reported in 89.4%, stricturing in 5.3%, and penetrating in 5.3%. Perianal disease was found in 10.5%. UGICD was complicated by stricture formation in 2 patients (esophageal and gastric). Conclusions: The prevalence of UGICD is considered high among CD Saudi patients who undergo upper GI endoscopy at baseline, and is asymptomatic in 47.4% of patients. This reported prevalence is not dissimilar from reports originating from Western countries. (Intest Res 2020;18:210-218)

      • KCI등재

        Assessment of effect of accelerated aging on interim fixed dental materials using digital technologies

        Omar Alageel,Omar Alsadon,Haitham Almansour,Abdullah Alshehri,Fares Alhabbad,Majed Alsarani 대한치과보철학회 2022 The Journal of Advanced Prosthodontics Vol.14 No.6

        PURPOSE. This study assessed the physical and mechanical properties of interim crown materials fabricated using various digital techniques after accelerated aging. MATERIALS AND METHODS. Three groups of interim dental restorative materials (N = 20) were tested. The first group (CO) was fabricated using a conventional manual method. The second group (ML) was prepared from prefabricated resin blocks for the milling method and cut into specimensizes using a cutting disc. The third group (3D) was additively manufactured using a digital light-processing (DLP) 3D printer. Aging acceleration treatments using toothbrushing and thermocycling simulators were applied to half of the specimens corresponding to three years of usage in the oral environment (N = 10). Surface roughness (Ra), Vickers microhardness, 3-point bending, sorption, and solubility tests were performed. A 2-way analysis of variance (ANOVA) and Fisher’s multiple comparison test were used to compare the results among the groups. RESULTS. The mean surface roughness (Ra) of the resin after accelerated aging was significantly higher in the CO and ML groups than that before aging, but not in the 3D group. All groups showed reduced hardness after accelerated aging. The flexural strength values were highest in the 3D group, followed by the ML and CO groups after accelerated aging. Accelerated aging significantly reduced water sorption in the ML group. CONCLUSION. According to the tested material and 3D printer type, both 3D-printed and milled interim restoration resins showed higher flexural strength and modulus, and lower surface roughness than those prepared by the conventional method after accelerated aging.

      • Survival and Prognostic Factors for Hepatocellular Carcinoma: an Egyptian Multidisciplinary Clinic Experience

        Abdelaziz, Ashraf Omar,Elbaz, Tamer Mahmoud,Shousha, Hend Ibrahim,Ibrahim, Mostafa Mohamed,El-Shazli, Mostafa Abdel Rahman,Abdelmaksoud, Ahmed Hosni,Aziz, Omar Abdel,Zaki, Hisham Atef,Elattar, Inas An Asian Pacific Journal of Cancer Prevention 2014 Asian Pacific journal of cancer prevention Vol.15 No.9

        Background: Hepatocellular carcinoma (HCC) is a dismal tumor with a high incidence, prevalence and poor prognosis and survival. Management of HCC necessitates multidisciplinary clinics due to the wide heterogeneity in its presentation, different therapeutic options, variable biologic behavior and background presence of chronic liver disease. We studied the different prognostic factors that affected survival of our patients to improve future HCC management and patient survival. Materials and Methods: This study is performed in a specialized multidisciplinary clinic for HCC in Kasr El Eini Hospital, Cairo University, Egypt. We retrospectively analyzed the different patient and tumor characteristics and the primary mode of management applied to our patients. Further analysis was performed using univariate and multivariate statistics. Results: During the period February 2009 till February 2013, 290 HCC patients presented to our multidisciplinary clinic. They were predominantly males and the mean age was $56.5{\pm}7.7years$. All cases developed HCC on top of cirrhosis that was mainly due to HCV (71%). Most of our patients were Child-Pugh A (50%) or B (36.9%) and commonly presented with small single lesions. Transarterial chemoembolization was the most common line of treatment used (32.4%). The overall survival was 79.9% at 6 months, 54.5% at 1 year and 22.4% at 2 years. Serum bilirubin, site of the tumor and type of treatment were the significant independent prognostic factors for survival. Conclusions: Our main prognostic variables are the bilirubin level, the bilobar hepatic affection and the application of specific treatment (either curative or palliative). Multidisciplinary clinics enhance better HCC management.

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