Browsing Mathematics, Statistics & Physics by Title

Now showing items 545-564 of 687

    • Preliminay test estimation in the two parameter exponential distribution based on record values 

      Baklizi, Ayman (2010 , Article)
      We considered estimation of the parameters of the exponential distribution based on record data in the presence of prior information. Preliminary test and shrinkage estimators are developed and their properties are ...

    • Preparation, spectroscopic and structural studies on charge-transfer complexes of 2,9-dimethyl-1,10-phenanthroline with some electron acceptors 

      Gaballa, Akmal S.; Wagner, Christoph; Teleb, Said M.; Nour, El-Metwally; Elmosallamy, M.A.F.; ... more authors ( Elsevier , 2007 , Article)
      Charge-transfer (CT) complexes formed in the reactions of 2,9-dimethyl-1,10-phenanthroline (Me2phen) with some acceptors such as chloranil (Chl), picric acid (HPA) and chloranilic acid (H2CA) have been studied in the defined ...

    • Prevalence and correlates of autism spectrum disorder in Qatar: a national study 

      Alshaban F.; Aldosari M.; Al-Shammari H.; El-Hag S.; Ghazal I.; ... more authors ( Blackwell Publishing Ltd , 2019 , Article)
      Background Few epidemiological data on autism spectrum disorders (ASD) exist for Arabic countries. We conducted the first survey of ASD in Qatar, a population with high consanguinity level. Methods This cross‐sectional ...

    • Prevalence of hepatitis B and C viruses among migrant workers in Qatar. 

      Nasrallah, Gheyath K; Chemaitelly, Hiam; Ismail, Ahmed I A; Nizamuddin, Parveen B; Al-Sadeq, Duaa W; ... more authors ( Springer Nature , 2024 , Article)
      Limited data exist on viral hepatitis among migrant populations. This study investigated the prevalence of current hepatitis B virus (HBV) infection and lifetime hepatitis C virus (HCV) infection among Qatar's migrant craft ...

    • Production of flexible nanocomposite membranes for x-ray detectors 

      Ahmad I., Ayesh; Salah, Belal; Nawwas, Rama; Alyafei, Aldana; AlMansouri, Sara; ... more authors ( Elsevier , 2020 , Article)
      Flexible membranes of poly(vinyl alcohol) (PVA) polymer and CuO nanoparticles for x-ray detection applications are reported in this work. PVA represents a polymer matrix for nanoparticles, and its flexibility and electrical ...

    • Production of hazardous gas sensors using spinel ferrite nanoparticles 

      Ayesh, Jocelyn; Abu Haija, Mohammad ( Hamad bin Khalifa University Press (HBKU Press) , 2018 , Conference Paper)
      This work reports on sensitive and selective gas sensors based on copper ferrite (CuFe2O4) nanoparticles. The nanoparticles were produced different methods including: colloid microwave assisted hydrothermal method, and ...

    • Production of hazardous gas sensors using spinel ferrite nanoparticles 

      Ayesh, Ahmad Ibrahim ( Hamad bin Khalifa University Press (HBKU Press) , 2018 , Conference Paper)
      This work reports on sensitive and selective gas sensors based on copper ferrite (CuFe2O4) nanoparticles. The nanoparticles were produced different methods including: colloid microwave assisted hydrothermal method, and ...

    • Production of metal-oxide nanoclusters using inert-gas condensation technique 

      Ayesh, Ahmad I. ( Elsevier B.V. , 2017 , Article)
      Inert-gas condensation is a novel technique that can be used to produce nanoclusters for different applications. In the present work, dc sputtering combined with inert-gas condensation were used to produce copper oxide ...

    • Production of sensitive gas sensors using CuO/SnO2 nanoparticles 

      Ayesh A.I.; Alyafei A.A.; Anjum R.S.; Mohamed R.M.; Abuharb M.B.; ... more authors ( Springer Verlag , 2019 , Article)
      Metal oxide nanoparticles, such as CuO and SnO2, are outstanding systems for H2S gas sensing in air. In this work, those nanoparticles were deposited with different mixing percentages on substrates to form percolating ...

    • Production Of Size-selected Copper Nanoclusters For Petroleum Refinery Applications 

      Ayesh, Ahmad ( Hamad bin Khalifa University Press (HBKU Press) , 2014 , Conference Paper)
      Atomic nanoclusters exhibit large surface to volume ratio which enhances their ability to interact with external materials, thus, they can be utilized efficiently for catalysts and gas sensing applications. Copper (Cu) ...

    • Proposing a Nondestructive and Intelligent System for Simultaneous Determining Flow Regime and Void Fraction Percentage of Gas-Liquid Two Phase Flows Using Polychromatic X-Ray Transmission Spectra 

      Amiri, Saba; Ali, Peshawa Jammal Muhammad; Mohammed, Shivan; Hanus, Robert; Abdulkareem, Lokman; ... more authors ( Springer , 2021 , Article)
      Two phase flows are of particular importance in various research fields. In the current article, a novel system consists of an X-ray tube and one sodium iodide crystal detector with ability of determining type of flow ...

    • Protection from previous natural infection compared with mRNA vaccination against SARS-CoV-2 infection and severe COVID-19 in Qatar: a retrospective cohort study 

      Hiam, Chemaitelly; Ayoub, Houssein H; AlMukdad, Sawsan; Coyle, Peter; Tang, Patrick; ... more authors ( Elsevier , 2022 , Article)
      BackgroundUnderstanding protection conferred by natural SARS-CoV-2 infection versus COVID-19 vaccination is important for informing vaccine mandate decisions. We compared protection conferred by natural infection versus ...

    • Protection of Omicron sub-lineage infection against reinfection with another Omicron sub-lineage 

      Chemaitelly, Hiam; Ayoub, Houssein H.; Coyle, Peter; Tang, Patrick; Yassine, Hadi M.; ... more authors ( Nature Research , 2022 , Article)
      There is significant genetic distance between SARS-CoV-2 Omicron (B.1.1.529) variant BA.1 and BA.2 sub-lineages. This study investigates immune protection of infection with one sub-lineage against reinfection with the other ...

    • Pt-Based Nanostructures for Electrochemical Oxidation of CO: Unveiling the Effect of Shapes and Electrolytes 

      Abdelgawad, Ahmed; Salah, Belal; Eid, Kamel; Abdullah, Aboubakr M.; Al-Hajri, Rashid S.; ... more authors ( MDPI , 2022 , Article)
      Direct alcohol fuel cells are deemed as green and sustainable energy resources; however, CO-poisoning of Pt-based catalysts is a critical barrier to their commercialization. Thus, investigation of the electrochemical CO ...

    • Pt-doped armchair graphene nanoribbon as a promising gas sensor for CO and CO2: DFT study 

      Ehab, Salih; Ayesh, Ahmad I. ( Elsevier , 2021 , Article)
      In this work, four armchair graphene nanoribbon (AGNR) based sensor materials were built using Atomistic ToolKit Virtual NanoLab (ATK-VNL) and utilized to detect carbon monoxide (CO) and carbon dioxide (CO2) gases. First, ...

    • Quadratic problems with two quadratic constraints: Convex quadratic relaxation and strong lagrangian duality 

      Hamdi, A.; Taati, A.; Almaadeed, T.A. ( EDP Sciences , 2021 , Article)
      In this paper, we study a nonconvex quadratic minimization problem with two quadratic constraints, one of which being convex. We introduce two convex quadratic relaxations (CQRs) and discuss cases, where the problem is ...

    • Quantization of the Szekeres system 

      Paliathanasis A.; Zampeli A.; Christodoulakis T.; Mustafa M.T. ( Institute of Physics Publishing , 2018 , Article)
      We study the quantum corrections on the Szekeres system in the context of canonical quantization in the presence of symmetries. We start from an effective point-like Lagrangian with two integrals of motion, one corresponding ...

    • Radioactivity levels in the marine environment along the Exclusive Economic Zone (EEZ) of Qatar 

      Al-Qaradawi, Ilham; Abdel-Moati, Mohamed; Al-Yafei, Mohsin Al-Ansi; Al-Ansari, Ebrahim; Al-Maslamani, Ibrahim; ... more authors ( Elsevier , 2015 , Article)
      A study on 137Cs, 40K, 226Ra, 228Ra, and 238U was carried out along the EEZ of Qatar. Results serve as the first ever baseline data. The level of 137Cs (mean value 1.6 ± 0.4 Bq m 3) in water filters was found to be in the ...

    • Radon concentration determination in some dwellings of Doha city of Qatar 

      Arafa, W.; El-Karadawi, E. ( Elsevier , 1997 , Article)
      Yearly average radon concentrations have not been reported yet in Qatar. Only few measurements on indoor radon concentrations have been conducted during the autumn season in 1992. To complete these measurements a determination ...

    • Re-emission of slow positrons from tungsten at elevated temperatures 

      Al-Qaradawi, I. Y.; Coleman, P. G. ( Elsevier , 2002 , Conference Paper)
      A series of measurements have been made on the dependence of the intensity and energy spectrum of slow positrons re-emitted from polycrystalline tungsten foil held at temperatures of up to 500 °C. Irrespective of target ...