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Wormholes in Higher Dimensions with Non-Linear Curvature Terms from Quantum Gravity Corrections
Ahmad Rami El-Nabulsi 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.5
In this work, we discuss a 7-dimensional universe in the presence of a static traversable wormhole and a decaying cosmological constant and dominated by higher-order curvature effects expected from quantum gravity corrections. We confirmed the existence of wormhole solutions in the form of the Lovelock gravity. Many interesting and attractive features are discussed in some detail.
El-Nabulsi Rami Ahmad 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.79 No.4
We present a new viable modified theory of gravity in which the matter sector is characterized by a logarithmic Lagrangian density. The modified Einstein’s field equations are derived, and they are characterized by the emergence of an effective gravitational coupling constant and an effective negative cosmological constant both coupled to the Lagrangian of matter. Applied to the Friedmann-Robertson-Walker cosmological framework, it leads to motivating phenomenology. In particular, the universe is free from the initial singularity, and a unified description of the early inflationary phase, the succeeding non-accelerating, matter-dominated expansion, and then the transition to a late-time accelerating phase is obtained as well. Moreover, the effective dark energy sector can be quintessence, yet the universe starts contracting if the phantom divide-line is crossed. The model is confronted with observations that agree with recent astronomical data. Moreover, the model gives rise to Einstein’s field equations which resemble the equations obtained in unimodular gravity.
Accelerated universe with a traversable wormhole from Visser's massive gravity
El-Nabulsi Rami Ahmad 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.78 No.1
In this letter, the Friedmann–Robertson–Walker model with a traversable wormhole is considered from the view point of Visser’s massive gravity theory. If the matter in the universe is assumed to be divided into two parts, the cosmic part, which depends on time only, and the wormhole part which depends on space only, a late-time acceleratedly expanding universe with a traversable wormhole and dominated by phantom energy is obtained.
Characterization and Performance Evaluation of Advanced Aircraft Electric Power Systems
Ahmad Eid,Hassan El-Kishky,Mazen Abdel-Salam,Mohamed T. El-Mohandes 전력전자학회 2010 JOURNAL OF POWER ELECTRONICS Vol.10 No.5
A model of an advanced aircraft electric power system is developed and studied under variable-speed constant-frequency (VSCF) operation. The frequency of the generator’s output voltage is varied from 400-㎐ to 800-㎐ for different loading scenarios. Power conversions are obtained using 12-pulse power converters. To reduce the harmonic contents of the generator output waveforms, two high-pass passive filters are designed and installed one at a time at the generator terminals. The performance of the two passive filters is compared according to their losses and effectiveness. The power quality characteristics of the studied VSCF aircraft electric power system are presented and the effectiveness of the proposed filter is demonstrated through compliance with the newly published aircraft electrical standards MIL-STD-704F.
Effect of perforation patterns on the fundamental natural frequency of microsatellite structure
Ahmad M. Baiomy,M. Kassab,B.M. El-Sehily,R.M. El-Kady Techno-Press 2023 Advances in aircraft and spacecraft science Vol.10 No.3
There is a burgeoning demand for minimizing the mass of satellites because of its direct impact on reducing launch-to-orbit cost. This must be done without compromising the structure's efficiency. The present paper introduces a relatively low-cost and easily implementable approach for optimizing structural mass to a maximum natural frequency. The natural frequencies of the satellite are of utmost pertinence to the application requirements, as the sensitive electronic instrumentation and onboard computers should not be affected by the vibrations of the satellite structure. This methodology is applied to a realistic model of Al-Azhar University micro-satellite in partnership with the Egyptian Space Agency. The procedure used in structural design can be summarized in two steps. The first step is to select the most favorable primary structural configuration among several different candidate variants. The nominated variant is selected as the one scoring maximum relative dynamic stiffness. The second step is to use perforation patterns reduce the overall mass of structural elements in the selected variant without changing the weight. The results of the presented procedure demonstrate that the mass reduction percentage was found to be 39% when compared to the unperforated configuration that had the same plate thickness. The findings of this study challenge the commonly accepted notion that isogrid perforations are the most effective means of achieving the goal of reducing mass while maintaining stiffness. Rather, the study highlights the potential benefits of exploring a wider range of perforation unit cells during the design process. The study revealed that rectangular perforation patterns had the lowest efficiency in terms of modal stiffness, while triangular patterns resulted in the highest efficiency. These results suggest that there may be significant gains to be made by considering a broader range of perforation shapes and configurations in the design of lightweight structures.
Characterization and Performance Evaluation of Advanced Aircraft Electric Power Systems
Eid, Ahmad,El-Kishky, Hassan,Abdel-Salam, Mazen,El-Mohandes, Mohamed T. The Korean Institute of Power Electronics 2010 JOURNAL OF POWER ELECTRONICS Vol.10 No.5
A model of an advanced aircraft electric power system is developed and studied under variable-speed constant-frequency (VSCF) operation. The frequency of the generator's output voltage is varied from 400-Hz to 800-Hz for different loading scenarios. Power conversions are obtained using 12-pulse power converters. To reduce the harmonic contents of the generator output waveforms, two high-pass passive filters are designed and installed one at a time at the generator terminals. The performance of the two passive filters is compared according to their losses and effectiveness. The power quality characteristics of the studied VSCF aircraft electric power system are presented and the effectiveness of the proposed filter is demonstrated through compliance with the newly published aircraft electrical standards MIL-STD-704F.
Abd EL-Baset A. Ahmad,Ibtesam A. Alasbahi 한국신뢰성학회 2018 International Journal of Reliability and Applicati Vol.19 No.2
Partially accelerated life tests or accelerated life tests are frequently used in modern reliability engineering. In this paper, we consider estimation of the parameters of linear exponential distribution based on constant-stress partially accelerated life tests. The maximum likelihood and Bayesian methods of estimation are used for this purpose based on progressive Type-II censoring data. The posterior means is derived under the squarederror loss function. Lindleys approximation and Markov chain Monte Carlo method are used to approximate the posterior. Comparisons between maximum likelihood estimation, Lindleys approximation and Markov chain Monte Carlo method are made. Finally, we present two examples to illustrate all the methods of inference discussed here.
Maha Raafat Abd El Fadeel,Ashraf Taha El-Dakhly,Ahmad Mohammad Allam,Tarek Korany Farag,Alaa Abdel-Moneim El-kholy 대한백신학회 2020 Clinical and Experimental Vaccine Research Vol.9 No.2
Purpose: Bovine respiratory disease is a worldwide health concern in the feedlot cattle causing morbidity and mortality in young with major economic losses to the producer. Programs of vaccination are integral parts of preventive health programs. We aim to prepare and evaluate lyophilized combined inactivated viruses (bovine viral diarrhea virus [BVDV] genotypes 1 and 2, bovine herpes virus type 1.1 [BoHV-1.1], bovine parainfluenza-3 virus [BPI-3V], and bovine respiratory syncytial virus [BRSV]) vaccine using saponin as a solvent and adjuvant in cattle. Materials and Methods: Lyophilized Pneumo-5 vaccine was formulated to include the inactivated BVDV genotypes 1 and 2, BoHV-1.1, BPI-3V, and BRSV. The saponin solution was used as an adjuvant and solvent. The prepared vaccines were adjusted to contain 1- and 1.5-mg saponin/dose. It was evaluated for its sterility, safety, and potency in mice and calves. The antibody titers in vaccinated calves were measured by virus neutralization test and enzyme-linked immunosorbent assay (ELISA). Results: The Pneumo-5 vaccine was found to be free from any contaminants and safe in mice. Meanwhile, the vaccine showed safety in calves which inoculated intramuscularly with the double dose of the vaccines. The overall immune response reached its peak in the 2nd-month post-vaccination. The vaccine contained saponin 1.5 mg/dose reached its antibodies peak in the 4th-week post-vaccination. All groups of vaccinated calves with both concentrations of the saponin did not show statistical significance in antibody titers measured by serum neutralization test and/or ELISA. Conclusion: The prepared vaccine, namely Pneumo-5, and adjuvanted with either 1 or 1.5 mg/dose saponin was proved safe and potent for effectual protection of calves against BVDV genotypes 1 and 2, BoHV-1.1, BPI-3V, and BRSV.
Omran, Dalia Abd El Hamid,Awad, AbuBakr Hussein,Mabrouk, Mahasen Abd El Rahman,Soliman, Ahmad Fouad,Aziz, Ashraf Omar Abdel Asian Pacific Journal of Cancer Prevention 2015 Asian Pacific journal of cancer prevention Vol.16 No.1
Background:Hepatocellular carcinoma (HCC) is the second most common malignancy in Egypt. Data mining is a method of predictive analysis which can explore tremendous volumes of information to discover hidden patterns and relationships. Our aim here was to develop a non-invasive algorithm for prediction of HCC. Such an algorithm should be economical, reliable, easy to apply and acceptable by domain experts. Methods: This cross-sectional study enrolled 315 patients with hepatitis C virus (HCV) related chronic liver disease (CLD); 135 HCC, 116 cirrhotic patients without HCC and 64 patients with chronic hepatitis C. Using data mining analysis, we constructed a decision tree learning algorithm to predict HCC. Results: The decision tree algorithm was able to predict HCC with recall (sensitivity) of 83.5% and precession (specificity) of 83.3% using only routine data. The correctly classified instances were 259 (82.2%), and the incorrectly classified instances were 56 (17.8%). Out of 29 attributes, serum alpha fetoprotein (AFP), with an optimal cutoff value of ${\geq}50.3ng/ml$ was selected as the best predictor of HCC. To a lesser extent, male sex, presence of cirrhosis, AST>64U/L, and ascites were variables associated with HCC. Conclusion: Data mining analysis allows discovery of hidden patterns and enables the development of models to predict HCC, utilizing routine data as an alternative to CT and liver biopsy. This study has highlighted a new cutoff for AFP (${\geq}50.3ng/ml$). Presence of a score of >2 risk variables (out of 5) can successfully predict HCC with a sensitivity of 96% and specificity of 82%.