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Tytuł:
Performance Enhancement of Cooperative MIMO-NOMA Systems Over Sub-6 GHz and mmWave Bands
Autorzy:
Saleh, Ahmed A.
Ahmed, Mohamad A.
Powiązania:
https://bibliotekanauki.pl/articles/24200732.pdf
Data publikacji:
2023
Wydawca:
Instytut Łączności - Państwowy Instytut Badawczy
Tematy:
error probability
MIMO
mmWave
NOMA
out-age probability
power allocation factor
successive-interference cancellation (SIC
Opis:
In this paper, two radio links with different frequency bands are considered for base stations (BS) serving users via decode-and-forward (DF) cooperative relays. Backhaul and access links are proposed with sub-6 GHz and millimeter wave (mmWave) bands, respectively. Non-orthogonal multiple access (NOMA) is employed in the backhaul link to simultaneously transmit a superposed signal in the power domain, using the same band. The superposed signals, containing two signals that differ in terms of power allocation factors (PAFs), are designed for two selected DF relays in the BS. The two relays are chosen from several relays to be serviced by the BS based on a pairing algorithm that depends on different users’ circumstances. The furthest DF relay detects the incoming NOMA signal directly, while the nearest one applies successive interference cancellation (SIC) before extracting its signal. Each DF relay forwards the detected signals toward their intended users over mmWave channels. Three performance metrics are utilized to evaluate the system’s performance: outage probability, achievable throughput, and bit error rate. Comparisons between two mmWave bands in the access link (28 and 73 GHz) are made to demonstrate the superiority of the 28 GHz band in terms of the three performance-related metrics.
Źródło:
Journal of Telecommunications and Information Technology; 2023, 2; 70--77
1509-4553
1899-8852
Pojawia się w:
Journal of Telecommunications and Information Technology
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Extended results of the Hadamard product of simple sets of polynomials in hypersphere
Autorzy:
Ahmed, A. El-Sayed
Powiązania:
https://bibliotekanauki.pl/articles/746574.pdf
Data publikacji:
2006
Wydawca:
Polskie Towarzystwo Matematyczne
Tematy:
Basic sets of polynomials
Hadamard product
several complex variables
Opis:
In this paper we study some extended results of the Hadamard product set for several simple monic sets of polynomials of several complex variables in hyperspherical regions, then we obtain the effectiveness conditions for this Hadamard product in hyperspherical regions.
Źródło:
Commentationes Mathematicae; 2006, 46, 2
0373-8299
Pojawia się w:
Commentationes Mathematicae
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
WIKIS IN EFL WRITING CLASSES IN SAUDI ARABIA: IDENTIFYING INSTRUCTORS’ REFLECTIONS ON MERITS, DEMERITS AND IMPLEMENTATION
Autorzy:
Khateeb, Ahmed A. Al
Powiązania:
https://bibliotekanauki.pl/articles/955902.pdf
Data publikacji:
2013
Wydawca:
Uniwersytet Marii Curie-Skłodowskiej w Lublinie. IATEFL Poland Computer Special Interest Group
Tematy:
web 2
0
social learning
merits
demerits
implementation
reflections
Opis:
This paper presents the pre-and-post-reflections of English language instructors concerning the incorporation of a new pedagogy in English as foreign language (EFL) writing classes in the Kingdom of Saudi Arabia. This approach is to integrate and blend wiki-mediated writing into a different course plan, with tasks that fit with the normal syllabi used for teaching writing skills. The methodology took a qualitative approach, specifically by conducting semi-structured pre-and-post-interviews. The qualitative analysis focused on the most frequent themes which occur in both cohorts. The participants, who were faculty members in the chosen institution, gave their reflections after they were shown the processes, thoughts and outcomes produced by the participants who actually applied the course and relevant tasks. It is important to identify instructors’ perspectives as this practice can be applied to enhance (novice) non-native learners of writing in English for academic purposes (EAP). Accordingly, this paper intends to shed light on three vital elements: merits, demerits and some principles for implementation.
Źródło:
Teaching English with Technology; 2013, 13, 4; 3-22
1642-1027
Pojawia się w:
Teaching English with Technology
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Servo tracking of targets at sea
Autorzy:
Ahmed, A.
Brdyś, M. A.
Powiązania:
https://bibliotekanauki.pl/articles/908404.pdf
Data publikacji:
2006
Wydawca:
Uniwersytet Zielonogórski. Oficyna Wydawnicza
Tematy:
śledzenie celu
urządzenie śledzące
filtr Kalmana
adaptacyjny układ sterowania
target tracking
tracker
Kalman filter
adaptive control
Opis:
This paper details a proposal for the position control system of a two-axis ship-mounted tracker. Aspects of the non-linear dynamics governing Line-Of-Sight (LOS) errors between the tracker and the target are presented. It is shown that the regulation of LOS errors can be achieved by introducing a feed-forward term based on the target’s velocity. This velocity is not measurable, and an estimator is required. Given that the tracking problem is non-linear, the classical separation principle does not hold, and cascading the estimator and regulator together may not lead to an optimal position control system. The ‘LQAdaptive’ system proposed here aims therefore to improve conformity to the separation principle. Simulation trials show that tracking is improved under the LQAdaptive system in comparison to a simple estimator-regulator structure.
Źródło:
International Journal of Applied Mathematics and Computer Science; 2006, 16, 2; 197-207
1641-876X
2083-8492
Pojawia się w:
International Journal of Applied Mathematics and Computer Science
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Chlorpyrifos Removal from Aqueous Solutions by Emulsion Liquid Membrane: Stability, Extraction, and Stripping Studies
Autorzy:
Al-Damluji, Farrah Emad
Mohammed, Ahmed A.
Powiązania:
https://bibliotekanauki.pl/articles/2202325.pdf
Data publikacji:
2023
Wydawca:
Polskie Towarzystwo Inżynierii Ekologicznej
Tematy:
emulsion liquid membrane
chlorpyrifos
emulsion droplet size
stability
mass transfer coefficient
extraction efficiency
Opis:
The current paper focuses on assessing key parameters affecting the extraction of Chlorpyrifos as well as emulsion stability using the emulsion liquid membrane technology. Five parameters affecting the extraction have been studied: homogenizer speed, emulsification time, agitating time, surfactant concentration, and stripping phase concentration taking into consideration the emulsion breaking. Experiments proved that using the resulting optimum values will maximize both extraction and stripping efficiencies (93.8% and 94.7% respectively), while minimizing the emulsion breakage (increasing the stability of emulsion) to 0.73% with no need to employ a carrier agent. A 10 min agitating time, 3% (v/v) Span 80 as a surfactant, 12700-rpm homogenizer speed, 0.25 M HCl as an internal phase concentration, and 5 min emulsification time are chosen to be the optimum parameters’ values. A study of extraction kinetics and estimation of mass transfer coefficient was also accomplished (3.89×10-9m/s). The conclusions of this work can be extended to the removal of other types of pesticides from water.
Źródło:
Journal of Ecological Engineering; 2023, 24, 2; 101--111
2299-8993
Pojawia się w:
Journal of Ecological Engineering
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Application of Emulsion Liquid Membrane Using Green Surfactant for Removing Phenol from Aqueous Solution: Extraction, Stability and Breakage Studies
Autorzy:
Mohammed, Ahmed A.
Al-Khateeb, Rasha Waleed
Powiązania:
https://bibliotekanauki.pl/articles/2025802.pdf
Data publikacji:
2021
Wydawca:
Polskie Towarzystwo Inżynierii Ekologicznej
Tematy:
ELM
emulsion liquid membrane
phenol
green surfactant
stability
extraction
Opis:
Emulsion Liquid Membrane (ELM) has garnered much attention, for its simple operation and high selectivity for the target solute. For an ELM process to be successful, emulsion stability and formulation of liquid membrane are the two main criteria. This study investigated an ELM formulation to identify a suitable green surfactant over the ordinary ones to reduce the utilization of chemicals. The stability of water-in-oil-in-water (w/o/w) was assessed in the following ways, by altering the concentrations of the egg yolk and NaOH, homogenizer speed, and emulsification time. To ascertain the favorable conditions for phenol extraction, several experiments were performed, adopting the batch process, which included many parameters, like the influence exerted by the pH of the external feed, concentration of surfactant, concentration of the internal phase, time of emulsification, homogenization speed and mixing time. Lower breakage and greater extraction efficiency (0.83% and 82.06%, respectively) were attained at 3.5 pH of the external feed, 4% (v/v) of the surfactant, 0.1 M of NaOH, 7 min of emulsification time, 5800 rpm of homogenizer speed and 3 minutes of mixing time. From the results of this study, egg yolk emerged as a good green surfactant. Thus, the ELM process holds promise as an effective technology for stripping phenol from aqueous solutions.
Źródło:
Journal of Ecological Engineering; 2022, 23, 1; 305-314
2299-8993
Pojawia się w:
Journal of Ecological Engineering
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Efficient removal of imidacloprid pesticide by two eco-friendly activated carbons
Autorzy:
Mohammad, Somaia Gaber
El-Refaey, Ahmed A.
Powiązania:
https://bibliotekanauki.pl/articles/27312663.pdf
Data publikacji:
2023
Wydawca:
Instytut Technologiczno-Przyrodniczy
Tematy:
activated carbon
hazelnut
imidacloprid
pesticide
regeneration
removal
walnut
Opis:
In this study, the removal of imidacloprid (IMD) pesticide onto activated carbon produced from nut shells of hazelnut (HAC), and walnut (WAC) has been investigated. The prepared activated carbons were characterised by total carbon, nitrogen and hydrogen content, surface areas and pore volume. Fourier-transform infrared (FTIR), and scanning electron microscopy (SEM) were studied before and after adsorption experiments. Effects of adsorbent dose (0.02-0.2 g), contact time (10-120 min), initial imidacloprid concentration (10-100 mg∙dm-3), and pH (1-8), and temperatures (25-50°C) on the removal of IMD pesticide by HAC and WAC in the batch mode were studied. The removal percentage of imidacloprid pesticide by HAC and WAC was 93.79% and 94.72%, respectively. The study showed that the pseudo-second-order kinetics model fitted well for both activated carbons. Moreover, adsorption isotherm results were evaluated using Freundlich, Langmuir and Temkin isotherm models. The adsorption results correlated well with the Langmuir isotherm model (R2 = 0.987 and 0.964) with maximum adsorption capacities of 76.923 and 83.333 mg∙g-1 for HAC and WAC, respectively, and an equilibrium time within 120 min. The nature of the adsorption of imidacloprid pesticide onto HAC and WAC is exothermic, spontaneous and physical in nature. The two prepared activated carbons (HAC, WAC) were successfully regenerated for three cycles and could be used as an effective and low-cost adsorbent for the removal of IMD pesticide from aqueous solutions. The production of the activated carbons of HAC and WAC will provide minimisation of these wastes in the environment.
Źródło:
Journal of Water and Land Development; 2023, 57; 220--230
1429-7426
2083-4535
Pojawia się w:
Journal of Water and Land Development
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Experimental investigation on performance of a spark ignition engine runs with alcoholic blend-gasoline
Autorzy:
Ahmed, H. A.
Powiązania:
https://bibliotekanauki.pl/articles/243048.pdf
Data publikacji:
2015
Wydawca:
Instytut Techniczny Wojsk Lotniczych
Tematy:
methanol
ethanol
butanol
compression ratio
specific fuel consumption
exhaust gas temperature
performance
Opis:
In this paper performance resulted from a single cylinder spark-ignition engine fuelled with 20% by volume of methanol, ethanol, and butanol was studied and compared to gasoline. The experiments were conducted at variable speed and maximum torques. The conditions of stoichiometric air–fuel ratio at wide-open throttle were used. The tests were perfumed at higher useful compression ratio of the used Iraqi gasoline. The test results show that the higher compression ratio for the tested gasoline was 7.5:1. So an Iraqi conventional gasoline has engine HUCR=7.5:1 and its OST= 19 ºBTDC, this compression ratio can be considered low. Adding 20% of alcoholic blends by volume to gasoline improved the engine performance. Within the tested speed range, alcoholic blends produced higher brake powers, volumetric efficiency and thermal efficiency. In addition, it resulted in lower exhaust gases temperatures. The brake specific fuel consumption of the tested alcoholic blend was higher than that for gasoline.
Źródło:
Journal of KONES; 2015, 22, 3; 249-256
1231-4005
2354-0133
Pojawia się w:
Journal of KONES
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Experimental study of degradation modes and their effects on reliability of photovoltaic modules after 12 years of field operation in the steppe region
Autorzy:
Saadsaoud, M.
Ahmed, A.
Er, Z.
Rouabah, Z.
Powiązania:
https://bibliotekanauki.pl/articles/1054959.pdf
Data publikacji:
2017-09
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
88.40.-J
88.40.H-
88.40.FF
Opis:
This paper presents an evaluation of the performance degradation of photovoltaic modules after twelve operation years in a steppe region environment in Algeria. The objective is to understand the different degradation modes of the photovoltaic modules and associated factors and their impact on the electrical properties (V_{oc}, I_{sc}, V_{max}, I_{max}, P_{max} and FF) using the degradation tests of IEC 61215 qualification standard and the electroluminescence test. The experimental results show that yearly degradation rates of the maximum power output P_{max} present the highest possible loss, ranging from 2.08% to 5.2%. Additionally, the results show that the short-circuit current I_{sc} comes second with yearly degradation rates spanning from 2.75% to 2.84%. Finally the open-circuit voltage V_{oc} is the least affected, with yearly degradation occurring from 0.01% to 4.25%.
Źródło:
Acta Physica Polonica A; 2017, 132, 3; 930-935
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Impact of wood-derived biochar on the hydraulic characteristics of compacted soils: Its influence on simulated farmland carbon sequestration
Autorzy:
Ahmed, A.
Kurian, J.
Satyanarayana, S.
Raghavan, V.
Powiązania:
https://bibliotekanauki.pl/articles/2083067.pdf
Data publikacji:
2021
Wydawca:
Polska Akademia Nauk. Instytut Agrofizyki PAN
Tematy:
soil biochar mixture
water retention
pore-size
distribution
hydraulic conductivity
carbon sequestration
Opis:
The addition of biochar is often proposed to increase agricultural soil quality and crop yield, while at the same time sequestering carbon from the atmosphere to help mitigate global climate change. In this research, the pore-size distribution, and saturated hydraulic conductivity of sandy loam and clay loam soils amended with varying dosages (0-10% dry basis) and two different particle sizes (0.5-420 μm (PS1) or 421-841 μm (PS2)) of wood-derived biochar were investigated under compacted conditions (5, 10, or 15 standard Proctor rammer blows (5B, 10B, or 15B, respectively)). In the 5B compacted SL (SL-5B) soil, the volume of the soil fissures and transmission pores decreased, while the volume of the storage pores (SP) increased with increasing wood-derived biochar dosage. 23.1±0.9% of the volume of the 5B compacted clay loam (CL-5B) are storage pores, this value increased to 27.4±2.0% upon amendment with 10% PS1. The saturated hydraulic conductivity of the sandy loam-5B soil amended with 10% PS1 decreased from 6.8±0.3 to 0.80±0.03 mm h-1. The sandy loam farmland C emissions decreased by 0.071 tC ha-1 y-1, whereas CL farmland C emissions decreased by 0.091 tC ha-1 y-1.
Źródło:
International Agrophysics; 2021, 35, 2; 167-177
0236-8722
Pojawia się w:
International Agrophysics
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Surface Concentration of Defects at Grain Boundaries in Sintered Alumina Determined by Positron Annihilation Lifetime Spectroscopy
Autorzy:
Kansy, J.
Si Ahmed, A.
Liebault, J.
Moya, G.
Powiązania:
https://bibliotekanauki.pl/articles/2028969.pdf
Data publikacji:
2001-11
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.70.Bj
77.84.Bw
61.72.Mm
Opis:
Sintered alumina samples of grain diameters spanning from 1.2 to 4.5μm have been investigated by positron annihilation lifetime spectroscopy. One series of samples was produced from material containing about 150 ppm impurities (mainly SiO$\text{}_{2}$). The second one was made from material having about 2700 ppm of various elements (SiO$\text{}_{2}$, MgO, CaO). Two models of positron trapping at grain boundaries are compared: The first one relates to the diffusion-limited regime; and the other one - to the transition-limited regime of trapping. As a result the relative change of surface concentration of defects at grain boundaries is determined. Additionally, the positron diffusion constant in bulk alumina at room temperature, D$\text{}_{+}$=0.36±10 cm$\text{}^{2}$/s, is estimated.
Źródło:
Acta Physica Polonica A; 2001, 100, 5; 737-742
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Compact Transverse Electric Silicon-on-Insulator Mode Converter for Mode-Division Multiplexer
Autorzy:
Sharaf, Mohamed H.
El-Mashade, Mohamed B.
Emran, Ahmed A.
Powiązania:
https://bibliotekanauki.pl/articles/2055263.pdf
Data publikacji:
2022
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
integrated optics
silicon-on-insulator waveguide
WDM & MDM systems
perturbation theory
integrated optical
devices
hybrid modes
guided waves
Opis:
On-chip optical-interconnect technology emerges as an attractive approach due to its ultra-large bandwidth and ultra-low power consumption. Silicon-on-insulator (SOI) wire waveguides, on the other hand, have been identified to potentially replace copper wires for intra-chip communication. To take advantage of the wide bandwidth of SOI waveguides, wavelengthdivision multiplexing (WDM) has been implemented. However, WDM have inherent drawbacks. Mode-division multiplexing (MDM) is a viable alternative to WDM in MIMO photonic circuits on SOI as it requires only one carrier wavelength to operate. In this vein, mode converters are key components in on-chip MDM systems. The goal of this paper is to introduce a transverse electric mode converter. The suggested device can convert fundamental transverse electric modes to first-order transverse electric ones and vice versa. It is based on small material perturbation which introduces gradual coupling between different modes. This device is very simple and highly compact; the size of which is 3 μm². Mathematical expressions for both the insertion loss and crosstalk are derived and optimized for best performance. In addition, three-dimensional finite-difference time-domain (3D-FDTD) simulations are performed in order to verify the mathematical model of the device. Our numerical results reveal that the proposed device has an insertion loss of 1.2 dB and a crosstalk of 10.1 dB. The device’s insertion loss can be decreased to 0.95 dB by adding tapers to its material perturbation.
Źródło:
International Journal of Electronics and Telecommunications; 2022, 68, 2; 275--280
2300-1933
Pojawia się w:
International Journal of Electronics and Telecommunications
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Optimization of Acetaminophen and Methylparaben Removal within Subsurface Batch Constructed Wetland Systems
Autorzy:
Mutar, Zahraa Hasan
Mohammed, Ahmed A.
Al-Baldawi, Israa Abdulwahab
Powiązania:
https://bibliotekanauki.pl/articles/2025734.pdf
Data publikacji:
2021
Wydawca:
Polskie Towarzystwo Inżynierii Ekologicznej
Tematy:
phytoremediation
ornamental plant
constructed wetland
PPCPs
central composite design
Opis:
The response surface methodology accompanied by Central Composite Design (CCD) was employed in this study to optimize the Alternanthera spp-based phytoremediation process for the individual removal of acetaminophen and methylparaben. Two operational variables, including concentration (A) (20, 60,100 mg/L) and sampling time (B) (7, 14, 21, and 35 days) were involved in the study for removal efficiency (Y) as response. CCD had required a total of 18 experiments for each compound. Analysis of variance (ANOVA) was conducted to verify the adequacy of the proposed mathematical models and revealed good agreement with the experimental data. The observed R2 values (0.9732 and 0.9870), adjusted R2 (0.9620 and 0.9816) and predicted R2 (0.9383 and 0.9721) for AC and MP, respectively, indicated that the developed models were significant at the 95% probability level. Concentration factor was found to be insignificant in the mathematical models; in contrast, sampling time was found to be of a crucial role. The removal of AC and MP were 89.23% and 64.48% under optimum conditions of A = 100 mg/L and B = 35 days respectively. The validation test confirmed the predicted results obtained by Central Composite Design, as the removals achieved under optimum conditions were 91.04% and 59.17% for AC and MP, respectively, which were in good agreement with the results proposed by the theoretical design.
Źródło:
Journal of Ecological Engineering; 2022, 23, 1; 228-239
2299-8993
Pojawia się w:
Journal of Ecological Engineering
Dostawca treści:
Biblioteka Nauki
Artykuł
Wyświetlanie 1-15 z 105

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