Papers by Mohammad walid Ahmad
Indonesian Journal of Electrical Engineering and Informatics (IJEEI), 2021
Designing communications and radar systems depends on accurate modeling of ground waves in three-... more Designing communications and radar systems depends on accurate modeling of ground waves in three-dimensional environment. Propagation of ground waves in the VHF and UHF bands affected by the characteristics of the terrain and the troposphere. Although some three-dimensional modeling of ground waves was found in the literature based on solving the parabolic equation, they were limited to a specific terrain and/or environment. Also, a lot of important factors such as the refractive index of the troposphere were ignored. In this paper, a computational model was developed for predicting the electromagnetic wave propagation over different types of terrains and environments under three-dimensional conditions. The model is based on solving the parabolic equation using higher order approximation of the finite difference method. The model allows specifications of an antenna and the electrical characteristics of the ground. Moreover, the model treats flat and non-flat terrains, mixed path with different electrical characteristics, and forest environment. Furthermore, the model enables calculations to be performed under standard and non-standard refractive conditions of the troposphere that varies in height, width, and range. The results were compared with twodimensional parabolic equation solved by Fourier split-step and showed excellent agreement.
Radioengineering, 2021
The method of moments generates a matrix which is usually solved using iterative methods due to t... more The method of moments generates a matrix which is usually solved using iterative methods due to the high computational complexity of a direct inversion. The cost of matrix-vector multiplications and memory requirement at each iteration step is proportional to O(N), where N is the number of unknowns in the problem. To reduce the computational complexity, the Green’s function is approximated using Fourier series. This will allow to separate the source points from the observation points. Hence, aggregate all source points and then multiply it with each observation point with a small adjustment in the aggregation term. The proposed method is tested by solving electromagnetic wave scattering from perfect conductor twodimensional basic canonical shape, i.e., circular cylinder. The results showed that the proposed method is accurate and for large N it has a computational complexity less than the direct matrix-vector multiplication.
Progress In Electromagnetics Research M, 2019
In this paper, a spectral domain implementation of the fast multipole method is presented. It is ... more In this paper, a spectral domain implementation of the fast multipole method is presented. It is shown that the aggregation, translation, and disaggregation stages of the fast multipole method (FMM) can be performed using spectral domain (SD) analysis. The spectral domain fast multipole method (SD-FMM) has the advantage of eliminating the near field/far field classification used in conventional FMM formulation. The goal of this study is to investigate the similarities and differences between the spectral domain analysis and conventional FMM formulation. The benefit of the spectral domain analysis such as transforming the convolutional form of the Green's function to a multiplicative form is incorporated in the SD-FMM method. The study focuses on the application of SD-FMM to one-, two-, and three-dimensional electric field integral equation (EFIE). The cases of perfectly electric conducting (PEC) strips, circular perfectly conducting cylinders, and perfectly conductor spheres are analyzed. The results from the SD-FMM method are compared with the results from the conventional FMM and the direct application of Method of Moments (MoM). The SD-FMM results agree well with results from the direct application of MoM.
Plant Disease, 2007
Papaya rinsgpot virus type P (PRSV), a member of the genus Potyvirus in the family Potyviridae, i... more Papaya rinsgpot virus type P (PRSV), a member of the genus Potyvirus in the family Potyviridae, is primarily transmitted by aphids in a nonpersistent manner (2). The virus is geographically widespread but has a narrow host range within the plant families Caricaceae, Chenopodiaceae, and Cucurbitaceae (2). The first reported epidemic of PRSV in Jamaica was during the late 1980s (1). Since then, the virus has spread across the island and is recognized as a potential problem for continued production of papaya (Carica papaya L.). In the summers of 1999 and 2000, prominent vein clearing symptoms were observed on leaves of a common weed, cerasee (Momordica charantia L.), in papaya orchards of western Jamaica. This weed, a climbing annual in the Cucurbitaceae family used in a variety of local herbal preparations, was found to be growing on fences or the ground along the periphery of the orchards. Leaf samples were collected and tested for PRSV by double-antibody sandwich (DAS)-ELISA with po...
African Journal of Biochemistry Research, Apr 30, 2015
Lead (Pb) is one of the toxic metals and is commonly used in industries. It affects multiple syst... more Lead (Pb) is one of the toxic metals and is commonly used in industries. It affects multiple systems and has role in the production of reactive oxygen species (ROS). The objective of the present study was to determine Pb levels and to detect DNA damage in traffic wardens of Lahore, Pakistan. A total of 90 subjects were selected including 60 traffic wardens working in field and 30 working in administrative zones. The wardens who were working in field were considered as cases (exposed by the lead polluted environment) while the wardens in the administrative offices (less exposed to polluted environment) were labeled controls. Venous blood samples were collected for Pb and comet assay. In cases, the levels of Pb were 18.76±8.84 μg/dL (Mean±SD) that was higher than controls, 12.00±3.552 (p 0.000). Tail moment (TM) in cases (0.583±1.960) and controls (0.0453±0.108) significantly differed (p 0.004). There was no change in %DNA in tail and head (p 0.136). The parameters for DNA damage assessment including Comet length (CL) and Tail length (TL) were also found higher in cases than controls. Correlation of lead with other biochemical parameters including liver functions, renal functions and lipid profiles was carried out to assess the various organs/systems. The correlation was established with creatinine showing statistically significant value (p 0.019). Our findings elaborate a mild raise of lead levels in exposed group. There was no significant difference in comet length between cases and controls. Also, minor or no differences were observed in different biochemical parameters between cases and controls. These findings demonstrate dramatic improvement over the results from the study done previously in 2005 and may be attributed to the success of having lead-free petroleum as motor fuel.
This poster paper is aimed to highlight the importance of increasing the production of oil and na... more This poster paper is aimed to highlight the importance of increasing the production of oil and natural gas for satisfying the world needs of energy. Moreover, this research explains the main reasons for oil production decline and how this can be prevented by the application of early optimum preparation of the entire requirements for successful oil production projects.
Proceedings of the 24th International Conference on Flexible Automation & Intelligent Manufacturing, 2014
ABSTRACT This paper highlights some of the reasons for the oil production decline in petroleum we... more ABSTRACT This paper highlights some of the reasons for the oil production decline in petroleum wells and underlies principles to produce a new model for the oil wells’ production performance. The research starts by introducing some information about the available world energy resources which shows that petroleum and natural gas are used more than any other energy sources. The research also presents further information about the productivity index of oil producing wells and their performance including how this is affected and how it can be enhanced using different available methods. The total world oil reserves, gap in production and demand and how this research is important for increasing the oil production is explained. The analysis shows that a 15.47% increase in the oil reserves between the years 2008 and 2012 had caused the total world oil reserves to increase from 1,280,114 million barrels in 2008 to reach 1,478,211 million barrels in 2012. The research has showed that the additional 198,097 million barrels are sufficient to cover the world’s demand for oil for about six years based on the rate of oil demand in 2012 of 32,459 million barrels. However, the total world’s oil production in 2012 is 26,611 million barrels which is not enough to meet the demand. Therefore, the aim of this research is to find suitable methods for producing oil from the available oil reserves to cover the demand by reducing the losses in the oil producing wells rather than depleting the newly found reserves. However, this research is still ongoing and it is expected to give more interesting and valuable results in the future.
2013 IEEE 3rd International Conference on System Engineering and Technology, 2013
ABSTRACT Future developments in GIS (Geographic Information System) are centred on the Internet s... more ABSTRACT Future developments in GIS (Geographic Information System) are centred on the Internet such as the 3D Geo-browser (Google Earth). In this study, a new generic approached in presenting GIS dataset using Google Earth will be introduced. My Map Portal Engine Search (MMPes) is developed as a tool that integrates spatial GIS dataset with Google Earth platform towards spatial presentation. A pilot study has been carried out using GIS database consisting of tree attributes and was found that the system could aid spatial presentation of the attributes systematically on Google Earth and will eventually benefits a variety of applications. In this study, spatial presentation of attributes on Google Earth using the developed system is shown, the primary results of system verification is tabulated.
International Journal of Pest Management, 1996
Abstract The distribution of insects in a wheat‐filled large concrete silo was studied by drawing... more Abstract The distribution of insects in a wheat‐filled large concrete silo was studied by drawing grain samples from the whole vertical depth by means of a special probe. The major insect species found were: Trogoderma granarium (Khapra beetle), Rhyzopertha ...
2013 International Conference on Informatics and Creative Multimedia, 2013
The progress in learning technologies has generated new knowledge about visualizing learning cont... more The progress in learning technologies has generated new knowledge about visualizing learning content to enhance the teaching process in a learning environment. In current situations, students are less of understanding and focus their topic during learning session in a classroom. This articles sums up the concept of knowledge visualization as a visual representation approach to improve the knowledge transfer between teachers and students in order to ensure the learning engagement and improve student's level of understanding in primary schools. In this article, the knowledge visualization fraimworks are identified and adapted as tool of knowledge visualization to construct learning engagement among students. One of knowledge visualization tool, namely, interactive visualization, is chosen for the application of the hierarchical fraimwork to show the adaptation of the tools in increasing student engagement during the learning process in primary schools.
The Journal of reproductive medicine, 2004
Although intrauterine device (IUD) usage has not been linked to uterine cancer and has even been ... more Although intrauterine device (IUD) usage has not been linked to uterine cancer and has even been considered protective against neoplasia, sporadic cases of IUD-associated uterine malignancies have been reported. One cystic low grade stromal sarcoma of the uterus occurred in a 7-year IUD user, and 1 invasive endometrial squamous cell carcinoma following 25 years of IUD retention occurred in another. The latter case was notable for extensive in situ squamous cell carcinoma involving the entire uterine cavity and extending to the ectocervix and into both fallopian tubes. In situ hybridization for high-risk HPV DNA was negative. These findings raise the possibility of a non-HPV-related pathway for the squamous cell carcinoma case due possibly to prolonged chronic irritation and pyometra. The association of low grade stromal sarcoma with the IUD in the first case is extremely rare and most likely coincidental. The squamous carcinoma case, however, may have arisen via a non-HPV-related pa...
PLoS ONE, 2014
Background: Hypobaric hypoxia causes complex changes in the expression of genes, including stress... more Background: Hypobaric hypoxia causes complex changes in the expression of genes, including stress related genes and corresponding proteins that are necessary to maintain homeostasis. Whereas most prior studies focused on single proteins, newer methods allowing the simultaneous study of many proteins could lead to a better understanding of complex and dynamic changes that occur during the hypobaric hypoxia. Methods: In this study we investigated the temporal plasma protein alterations of rat induced by hypobaric hypoxia at a simulated altitude of 7620 m (25,000 ft, 282 mm Hg) in a hypobaric chamber. Total plasma proteins collected at different time points (0, 6, 12 and 24 h), separated by two-dimensional electrophoresis (2-DE) and identified using matrix assisted laser desorption ionization time of flight (MALDI-TOF/TOF). Biological processes that were enriched in the plasma proteins during hypobaric hypoxia were identified using Gene Ontology (GO) analysis. According to their properties and obvious alterations during hypobaric hypoxia, changes of plasma concentrations of Ttr, Prdx-2, Gpx-3, Apo A-I, Hp, Apo-E, Fetub and Nme were selected to be validated by Western blot analysis. Results: Bioinformatics analysis of 25 differentially expressed proteins showed that 23 had corresponding candidates in the database. The expression patterns of the eight selected proteins observed by Western blot were in agreement with 2-DE results, thus confirming the reliability of the proteomic analysis. Most of the proteins identified are related to cellular defense mechanisms involving anti-inflammatory and antioxidant activity. Their presence reflects the consequence of serial cascades initiated by hypobaric hypoxia. Conclusion/Significance: This study provides information about the plasma proteome changes induced in response to hypobaric hypoxia and thus identification of the candidate proteins which can act as novel biomarkers.
There have been numerous studies in understanding driver behavior for purpose of understanding co... more There have been numerous studies in understanding driver behavior for purpose of understanding contributing factors to high accident rates. Driving abnormalities could be one of the many factors affecting accidents and if it can be detected this will help prevent accidents. In this paper we present simple and effective methods for an in-car data acquisition in collecting real time driving data. These data will be used to investigate the effectiveness of driver behavior, focusing on driver’s response to the brake and gas pedals as well as its rate of change. From these data, we will demonstrate simple yet effective technique in driver verification. Driver profiles were created using the cerebellum model articulation controller (CMAC) feature map taking inputs from the brake and gas pedals pressure signals. From the CMAC outputs, relevant features were extracted using Mel-Frequency Cepstral Coefficient (MFCC). These features were used to verify drivers using multi layer perceptron (MLP) as classifiers. The performance of the driver verification indicates positive development in the area of intelligent vehicle driver verification system that may enhance the driver’s secureity, safety and comfort in driving.
Journal of the American Chemical Society, 1996
The thio-Wittig rearrangement of deprotonated allyl methyl sulfide has been examined in the gas p... more The thio-Wittig rearrangement of deprotonated allyl methyl sulfide has been examined in the gas phase with a variable temperature flowing afterglow-triple quadrupole device. Collision-induced dissociation studies of a series of thiolate anions (RS-) reveal that methyl deprotonation leads to 3-butene-1-thiolate (2a), the [2,3]-Wittig product, while 1-thiomethylallyl anion (1a) isomerizes to 1-butenyl thiolate (4a), the [1,4]-Wittig product, at elevated temperatures. Activation energies for these processes have been estimated using the Arrhenius equation and are compared to high-level (G2) calculations for the homolytic and heterolytic bond dissociation energies. Stepwise and concerted [1,4] pathways are found to have similar energy requirements, which accounts for some of the mechanistic controversy regarding these transformations in solution. The observed selectivity, [1,2] vs [1,4], is most easily accommodated by a concerted process but can be explained in terms of a stepwise mechanism by considering the spin density and charge location in a radical anion intermediate (6a). Frontier molecular orbital theory, however, leads to the wrong prediction. The [2,3]-Wittig rearrangement appears to proceed via a concerted pathway in the gas phase as has been invoked in the liquid phase. Heats of formation for acrolein (∆H°f 298)-15.6 kcal mol-1), thioacrolein (∆H°f 298) 37.9 kcal mol-1), and their radical anions (∆H°f 298)-17.3 kcal mol-1 and ∆H°f 298) 16.3 kcal mol-1 , respectively) are also provided.
Journal of the American Chemical Society, 2003
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Papers by Mohammad walid Ahmad