oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2020 ( 13 )

2019 ( 753 )

2018 ( 845 )

2017 ( 818 )

Custom range...

Search Results: 1 - 10 of 410719 matches for " Hesham M. El-Ashmawy "
All listed articles are free for downloading (OA Articles)
Page 1 /410719
Display every page Item
Tei Index versus Pro BNP as Predictors of Weaning Failure in Mechanically Ventilated Chronic Obstructive Pulmonary Disease Patients  [PDF]
Hesham M. El-Ashmawy, Tamer A. Helmy, Samier M. El-Awady, Doaa Hashad, Ahmed M. Nabil
Open Journal of Respiratory Diseases (OJRD) , 2015, DOI: 10.4236/ojrd.2015.53007
Abstract: Objective: This prospective cohort study was designed to assess the rule of myocardial performance (Tei) index and NT-Pro BNP serum levels in prediction of weaning failure in mechanically ventilated COPD patients. Methods: Forty patients with respiratory failure due to acute exacerbation of COPD were enrolled to this study. All patients underwent a comprehensive echocardiographic examination including tissue doppler imaging within first 12 hours of admission. NT-pro BNP serum levels were measured on admission. Patients were followed up for outcome of weaning failure. Results: Right ventricular Tei index was higher in patients with failed weaning in comparison to successfully weaned patients (mean 0.66 versus 0.36, P < 0.001), also left ventricular Tei index was higher in patients who failed to be weaned (mean 0.45 versus 0.36, P = 0.007). There was no difference in serum NT-Pro BNP between successfully weaned patients and patients with weaning failure. Right ventricular Tei index showed higher accuracy in predicting weaning failure than the left ventricular Tei index (AUC 0.932 versus 0.754), while serum NT-Pro BNP showed no discrimination in predicting weaning failure (AUC 0.556). Conclusion: Tei index was superior to NT-ProBNP in prediction of weaning failure in COPD patients.
Effect of the Radial Pressure Gradient on the Secondary Flow Generated in an Annular Turbine Cascade
Hesham M. El-Batsh
International Journal of Rotating Machinery , 2012, DOI: 10.1155/2012/509209
Abstract: This paper introduces an investigation of the effect of radial pressure gradient on the secondary flow generated in turbine cascades. Laboratory measurements were performed using an annular sector cascade which allowed the investigation using relatively small number of blades. The flow was measured upstream and downstream of the cascade using a calibrated five-hole pressure probe. The three-dimensional Reynolds Averaged Navier Stokes equations were solved to understand flow physics. Turbulence was modeled using eddy-viscosity assumption and the two-equation Shear Stress Transport (SST) k-ω model. The results obtained through this study showed that the secondary flow is significantly affected by the pressure gradient along blade span. The experimental measurements and the numerical calculations predicted passage vortex near blade hub which had larger and stronger values than that predicted near blade tip. The loss distribution revealed that secondary flow loss was concentrated near blade hub. It is recommended that attempts of reducing secondary flow in annular cascade should put emphasis on the passage vortex near the hub. 1. Introduction Large-scale steam and gas turbines are always used in power generation and industrial applications. Therefore, turbine efficiency and performance have major concern. The losses in a turbine can be divided into profile loss, secondary flow loss, and tip clearance loss. The profile loss is caused by the growth of the boundary layer on the blades. Secondary flow loss is generated due to the deflection through blade channel. Tip leakage loss is induced due to pressure difference between blade pressure side and blade suction side when the tip clearance gap exists. There are many factors which influence turbine losses. The pressure gradient, turbulence level, blade geometry, incoming velocity, and inlet boundary layer thickness represent important parameters affecting turbine efficiency. It is practically very difficult to perform detailed flow field measurements in an engine at operating conditions. Understanding the physics that governs the flow and the associated turbine cascade losses has been obtained through wind tunnel experiments. These laboratory tests not only allow detailed flow field measurements but also give the experimenter the possibility to investigate the effect of several parameters separately. Experimental studies using linear turbine cascades introduce the aspect of flow periodicity by arranging a number of blades of constant cross-sections separated by a constant pitch. Linear cascade experiments
Energy Efficiency Behavior in Heterogeneous Networks under Various Operating Situations of Cognitive Small Cells  [PDF]
Amr A. Fahmy, Asmaa M. Saafan, Hesham M. El-Badawy, Salwa El-Ramly
Wireless Engineering and Technology (WET) , 2015, DOI: 10.4236/wet.2015.61002
Abstract: Recently, several approaches were followed for the enhancement and better resource utilization in mobile networks; this is to achieve energy efficient consumption for production and delivery of an information bit. Using Cognitive Femto cells (as a member of the small base stations’ family) proves that, it is an efficient solution for achieving this goal[1]. The use of Energy Efficiency term η has become one of the major indices for measuring the performance of these systems. η is the measure of the overall system Capacity (C) in bps/Hz versus the Consumed Energy (E) in Joules [2]. In consistence with many researches, analytic models and empirical measurements, η will be investigated throughout the course of this work. Cognitive Base Stations (CBS) (as an element of the system model) which performs the traffic offloading operations is proved to enhance η performance. In this work, a combination of both analytic and simulation models are used to construct a practical system model. The obtained model is then used to illustrate the effect of different operational parameters that are involved in the η problem. On the other hand, the current paper tries to focus on the selection criteria that may be used to design the cooperative cognitive networks in order to achieve the best η indices. Both of CBSs radii as well as the inter-separation distances (between CBSs and MBS location) are examined to obtain best η index for different operation scenarios; in addition, both of capacity and energy consumption are taken into consideration based on practical operating measures. This work proposed several nonlinear equations with fixed parameters to be used by field engineers to achieve the results with minimum reduced computation complexity. So, the current work may be of importance for the regulator bodies as well as the cognitive mobile operators.
Novel Optimized Cross-Layer Design with Maximum Weighted Capacity Based Resource Allocation for AMC/HARQ Wireless Networks  [PDF]
Reham A. El-Mayet, Hesham M. El-Badawy, Salwa H. Elramly
Wireless Engineering and Technology (WET) , 2013, DOI: 10.4236/wet.2013.42012
Abstract:

To provide quality-of service (QoS) guarantees for heterogeneous applications, most recent wireless communications technologies and standards combine the error-correcting capability of hybrid automatic repeat request (HARQ) schemes at the data link layer (DLL) with the adaptation ability of the adaptive modulation and coding (AMC) modes at the physical layer (PHY) layer. This paper aims to investigate the aggregated system capacity as well as the breakdown of this capacity for different ACM modes in each HARQ scheme. This investigation was done by using maximum weighted capacity (MWC) resource allocation at the PHY layer in conjunction with a novel packet error rate (PER)-based scheduling at the medium access control (MAC) layer. As a result, the dominant AMC mode corresponding to channel SNR was available.

 

Performance Assessment for LTE-Advanced Networks with Uniform Fractional Guard Channel over Soft Frequency Reuse Scheme  [PDF]
Mahammad A. Safwat, Hesham M. El-Badawy, Ahmad Yehya, Hosni El-Motaafy
Wireless Engineering and Technology (WET) , 2013, DOI: 10.4236/wet.2013.44024
Abstract:

Dropping probability of handoff calls and blocking probability of new calls are two important Quality of Service (QoS) measures for LTE-Advanced networks. Applying QoS for Cell edge users in soft frequency reuse scheme in LTE system is a challenge as they already suffer from limited resources. Assigning some resources for handover calls may enhance dropping probability but this is in price of degradation in the blocking probability for new calls in cell-edge. Uniform Fractional Guard Channel (UFGC) is a call admission policy that provides QoS without reserving resources for handover calls. In this paper, the performance of Soft Frequency Reuse (SFR) in presence of Uniform Fractional Guard Channel (UFGC) will be investigated using queuing analysis. The mathematical model and performance metrics will be deduced in this assessment. The impact of UFGC will be evaluated in edge and core part separately. Then the optimal value for the parameter of UFGC will be obtained to minimize the blocking probability of new calls with the constraint on the upper bound on the dropping probability of handoff calls.

Analysis of Different Call Admission Control Strategies and Its Impact on the Performance of LTE-Advanced Networks  [PDF]
Mahammad A. Safwat, Hesham M. El-Badawy, Ahmad Yehya, Hosni El-Motaafy
Communications and Network (CN) , 2014, DOI: 10.4236/cn.2014.62016
Abstract:

The call admission control (CAC) optimizes the use of allocated channels against offered traffic maintaining the required quality of service (QoS). Provisioning QoS to user at cell-edge is a challenge where there is limitation in cell resources due to inter-cell interference (ICI). Soft Frequency Reuse is ICI mitigation scheme that controls the distribution of resources between users. In this paper, the Impact of four CAC schemes (Cutoff Priority scheme (CP), Uniform Fractional Guard Channel (UFGC), Limited Fractional Guard Channel (LFGC), New Call Bounding (NCB) scheme) at cell-edge have investigated using queuing analysis in a comparative manner. The comparison is based on two criteria. The first criterion guarantees a particular level of service to already admitted users while trying to optimize the revenue obtained. The second criterion determines the minimum of number of radio resources that provides hard constraints in both of blocking and dropping probabilities. The four schemes are compared at different scenarios of new and handover call arrival rates.

Influence of Nanocrystalline ZrO2 Additives on the Fracture Toughness and Hardness of Spark Plasma Activated Sintered WC/ZrO2 Nanocomposites Obtained by Mechanical Mixing Method  [PDF]
M. Sherif El-Eskandarany, Hesham M. A. Soliman, M. Omoric
Open Journal of Composite Materials (OJCM) , 2012, DOI: 10.4236/ojcm.2012.21001
Abstract: The present study reports the formation of ultrafine hard particles of nanocomposite WC with different additions of ZrO2 powders (0.5 - 20 vol.%). The initial mixed powders of WC with the desired ZrO2 concentrations were mechanically mixed for 360 ks (end-product) under argon gas atmosphere at room temperature, using high energy ball mill. The end-product consists of average grain size of about 17 nm in diameter. The obtained nanocomposite powders were consolidated into fully dense compact, using spark plasma sintering (SPS) technique in vacuum. The experimental results revealed that the consolidation step, which was conducted at 1673 K with uniaxial pressure ranging from 19.6 to 38.2 MPa for short time (0.18 ks), does not lead to dramatic grain growth in the powders so that the consolidated nanocomposite bulk objects maintain their nanocrystalline behavior, being fine grains with an average size of 63 nm in diameter. The relative densities of consolidated nanocomposite WC/ZrO2 materials increase from 99.1% for WC-0.5% ZrO2 to 99.93% for WC-20% ZrO2. The indentation fracture toughness of the composites can be tailored between 7.31 and 19.46 MPa/m1/2 by controlling the volume fraction of ZrO2 matrix from 0.5% to 20%. The results show that the Poisson’s ratio increased monotonically with increasing the ZrO2 concentrations to get a maximum value of 0.268 for WC-20% ZrO2. In the whole range of ZrO2 concentrations (0.5 - 20 vol.%), high hardness values (20.73 to 22.83 GPa) were achieved. The Young’s modulus tends to decrease with increasing the volume fraction of the ZrO2 matrix to reach a minimum value of 583.2 GPa for WC-20% ZrO2. These hard and tough WC/ZrO2 nanocomposites are proposed to be employed as higher abrasive-wear resistant materials.
Performance Enhancement for Adaptive Beam-Forming Application Based Hybrid PSOGSA Algorithm  [PDF]
Ahmed Magdy, Osama M. EL-Ghandour, Hesham F. A. Hamed
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2015, DOI: 10.4236/jemaa.2015.74014
Abstract: Recently researchers were interested in hybrid algorithms for optimization problems for several communication systems. In this paper, a novel algorithm based on hybrid PSOGSA technique (combination of Gravitational Search Algorithm and Particle Swarm Optimization) is presented to enhance the performance analysis of beam-forming for smart antennas systems using N elements for Uniform Circular Array (UCA) geometry. Complex excitations (phases) of the array radiation pattern are optimized using hybrid PSOGSA technique for a set of simultaneously incident signals. Our results have shown tremendous improvement over the previous work was done using Uniform Linear Array (ULA) geometry and standard GSA in terms of normalized array factor and computational speed for normalized fitness values.
Performance Analysis on a Dual External Cavity Tunable Laser ECTL Source  [PDF]
Ahmed Fawzy, Osama M. El-Ghandour, Hesham F. A. Hamed
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2015, DOI: 10.4236/jemaa.2015.74015
Abstract: This paper presents the diffraction effects on the performance of a dual external cavity tunable laser source, whose external cavities are constructed by micro electro mechanical systems (MEMS). One of the main problems in these structures is the optical diffraction as the emitting surface of the laser diode is usually quite limited in the transverse directions. The emitted beam diffracts rapidly in the air and only a small amount of light is coupled back to the source that usually limits the tuning range of the source. Device characteristics such as tuning range, wavelength shift and sensitivity are evaluated. New expression is used and multiple reflections inside external cavities are considered. The simulation results have shown that single external cavity has limited tuning range. It is shown that multiple reflections have significant effect in our model. To get a better engineering for the dual ECTL dimensions, diffraction effects must be taken into account.
Involvement of Male Youth into Accidents in Upper Egypt: Pattern and Risk Analysis  [PDF]
Raouf M. Afifi, Sameh Sh. Zaytou, Ahmed A. El Raggal, Amani Qulali, Hesham A. K. Ayoub
Health (Health) , 2015, DOI: 10.4236/health.2015.78114
Abstract: Background: Accidents pose a serious threat to health and economy in Egypt. Objectives: To identify and analyze the epidemiological factors associated with different types of accidents among adult males in Upper Egypt. Methods: A sample of 500 Egyptian males 20 - 28 years of age attending for health care at Quena University Hospital (QUH) or affiliated health institutions in South Egyptian governorates of Luxor and Red Sea was studied. The demographic, socioeconomic, and habitual data, as well as health status, medical history, and history of engagement into accidents for the recruits all were evaluated. Results: Accidents occurrences accounted up to 23/500 (4.6%) of the studied group. Road traffic accidents (RTAs) represented the highest percentage (30.4%), followed by street fights (21.7%) and animal bites (13.1%). Occupational accidents, electrical injuries, and near-drowning, all were equally encountered (8.7%), whereas falls and burns were least prevalent (4.3% each). Drug abuse, manual work, obesity, and having epilepsy were significant risk factors for accident injuries (OR = 6.35, 95% CI: 1.64 - 24.58, OR = 3.36, 95% CI: 1.22 - 9.73, OR = 4.81, 95% CI: 1.50 - 15.46, OR = 45.33, 95% CI: 3.94 - 518.01, respectively). Conclusions: Engagement of young Upper Egyptian males into accidents is alarming. Most of the accident mechanisms encountered are preventable. Enforcement of standard occupational, traffic and public safety laws is needed to minimize the burden of accidents upon the public health and economy in Upper Egypt.
Page 1 /410719
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.