Experimental Investigation of a Walk-in Refrigerator Performance Using R290 as a Retrofit for R22

A. R. El-Sayed,M. El Morsi,N. A. Mahmoud 대한설비공학회 2018 International Journal Of Air-Conditioning and Refr Vol.26 No.4

An experimental performance study is performed on a refrigeration system equipped with a scroll compressor and tested with R22 using an electronic expansion valve (EEV) as an expansion device and controlled by proportional-integral-derivative (PID) control method. The system is tested at −12∘C, −8∘C, −4∘C, 0∘C and 4∘C evaporator air temperature and 20∘C, 25∘C and 30∘C condenser inlet water temperature at 50 Hz compressor driving frequency and 50Hz evaporator fans driving frequency. R22 reached the set point at all temperatures except −12∘C evaporator temperature with 30∘C condenser temperature due to the severe increase in the compressor discharge temperature that could result in the lubricating oil burnout. Then, the system is retrofitted with a reciprocating compressor especially designed to be used with R290 and tested with R290 at the same evaporator and condenser temperatures using EEV as an expansion device. R290 reached all set points at all evaporator and condenser temperatures. Also, R290 was able to reach all evaporator temperatures at higher condenser temperatures, 35∘C and 40∘C, and this will be discussed in future work. The results show that using R290, the pulldown time decreases by 30.3–71.4%, the ON time ratio decreases by 1–23.6%, the compressor discharge temperature decreases by 46.6–81∘C, the refrigerant mass flow rate decreases by 28.8–50.4%, VRC decreases by 15.2–32.5%, the compressor power consumption decreases by 34.4–44.3% and coefficient of performance (COP) increases by 35–115.5%.

Stem cell-derived exosomes for dentin-pulp complex regeneration: a mini-review

Hammouda Dina A.,Mansour Alaa M,Saeed Mahmoud A.,Zaher Ahmed R.,Grawish Mohammed E. 대한치과보존학회 2023 Restorative Dentistry & Endodontics Vol.48 No.2

This mini-review was conducted to present an overview of the use of exosomes in regenerating the dentin-pulp complex (DPC). The PubMed and Scopus databases were searched for relevant articles published between January 1, 2013 and January 1, 2023. The findings of basic in vitro studies indicated that exosomes enhance the proliferation and migration of mesenchymal cells, as human dental pulp stem cells, via mitogen-activated protein kinases and Wingless-Int signaling pathways. In addition, they possess proangiogenic potential and contribute to neovascularization and capillary tube formation by promoting endothelial cell proliferation and migration of human umbilical vein endothelial cells. Likewise, they regulate the migration and differentiation of Schwann cells, facilitate the conversion of M1 pro-inflammatory macrophages to M2 anti-inflammatory phenotypes, and mediate immune suppression as they promote regulatory T cell conversion. Basic in vivo studies have indicated that exosomes triggered the regeneration of dentin-pulp–like tissue, and exosomes isolated under odontogenic circumstances are particularly strong inducers of tissue regeneration and stem cell differentiation. Exosomes are a promising regenerative tool for DPC in cases of small pulp exposure or for whole-pulp tissue regeneration.

Functionalization of Electrospun Poly(Acrylonitrile-co-Styrene/Pyrrole) Copolymer Nanofibers for Using as a High-performance Carrier for Laccase Immobilization

M. R. El-Aassar,Mahmoud H. M. A. Shibraen,Yasser R Abdel-Fattah,Ahmed A. Elzain 한국섬유공학회 2019 Fibers and polymers Vol.20 No.11

Enzyme immobilization onto nanomaterials is a strategy to overcome the difficulties of the free enzymesapplications where the immobilization process affords excellent reusability and operational stability against temperature andpH, and high surface area for the catalytic reaction. In this work, poly(Acrylonitrile-co-Styrene/Pyrrole), (poly(AN-co-ST/Py)), copolymer nanofibers were successfully fabricated using the electrospinning technique. Laccase enzyme from Trametesversicolor was immobilized onto functionalized poly(AN-co-ST/Py) nanofibers by covalent attachment usingpolyethylenediamine (PEI) via physical adsorption and multipoint covalent attachment to the functional groups onto thepolymeric surface. Since the relative activity of the immobilized Laccase depends on the amount of the coupled PEI onto thepolymeric nanofibers, a colorimetric assay via copper ions complex formation was applied for the estimation of the processyield. Accordingly, the various factors affecting the PEI coupling process such as concentration, time, pH and temperaturewere investigated; Besides their influence on the morphology of the resultant nanofibers. Furthermore, thermal and pHstability, storage stability, and reusability were evaluated and compared. The optimum reaction temperature and pH for theimmobilized enzyme were 70 oC and 6.0, respectively. The scanning electron microscopy (SEM) images showed that themodified nanofibers with PEI have kept its nanofibers structure and uniform morphology with an average diameter ofapproximately 559.2 nm. Within 35 days, the immobilization process reduces the activity loss from 59 % to 29 %, whilethermal incubation at 50 oC for 2 hrs causes activity loss for the free and immobilized enzymes by 65 % and 30 %respectively. Therefore, the prepared copolymer nanofibers proposed in this work showed promising potential forapplications to enzyme immobilization.

Secure Mobile Cloud Computing for Sensitive Data : Teacher Services for Palestinian Higher Education Institutions

Mahmoud M. Abu Ghosh,Rasha R. Atallah,Samy S. Abu Naser 보안공학연구지원센터 2016 International Journal of Grid and Distributed Comp Vol.9 No.2

Many Palestinian higher education institutions had a successful experience in utilizing Electronic Services and Electronic learning, such as all the academic services for student and lecturer, schedule lectures, exams schedule, viewing the academic information, grades report, printing transcript, registering courses, library services, Email services, News and Announcements, but these services are supported by web based applications or desktop application which restrict the access of the users using computers or laptops, But there is a lack in supporting these services with mobile. Especially when dealing with sensitive data as inserting grades for courses. So in this paper we present a system called Secure Mobile Cloud Computing for Sensitive Data: Teacher Services for Palestinian Higher Education Institutions (MCCTSs) which is a mobile application to facilities access using RSA algorithm to encrypt the data which sent and received through Cloud computing application. MCCTSs serve the lecturers of Palestinian higher education institutions. Agile methodology was adapted to develop MCCTSs application. MCCTSs users successfully insert the grades securely and encrypted any time anywhere using RSA algorithm. It is hoped that the result of this study will encourage the universities to engage MCCTSs in their services. From the results we obtained, it is proved that RSA provides protection for the data, which is stored in Cloud. Only authorized user can read the encrypted data and decrypt it. Even if anyone happens to read the data accidentally, the original meaning of the data will not be understood.

Comparison of the Heating Properties of LaB6 and CeB6 Due to the Back Comparison of the Heating Properties of LaB_6 and CeB_6 Due to the Back

Mahmoud Bakr,R. Kinjo,Y. W. Choi,M. Omer,K. Yoshida,S. Ueda,M. Takasaki,K. Ishida,N. Kimura,H. Zen,T. Sonobe,T. Kii,K. Masuda,H. Ohgaki 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.51

The heating property of LaB_6 and CeB_6 cathodes is investigated against the Back Bombardment (BB) effect in thermionic RF guns using numerical calculation of the stopping range and deposited heat power inside the cathode materials. Then the change in a cathode temperature and corresponding change of current density during 5.5 μs pulse duration are determined by solving two differential equations. The simulation results show that, the change of current density during the macropulse for LaB_6 two times higher than for CeB_6, hence, the effect of the BB electrons in CeB_6 is less than for LaB_6.

A close look at the influence of praseodymium (III) oxide on the structural, physical, and γ-ray protection capacity of a ternary B2O3–PbO–CdO glass system

Shoeir R.H.,Afifi M.,Dhmees Abdelghaffar S.,Sayyed M.I.,Mahmoud K.A. 한국원자력학회 2024 Nuclear Engineering and Technology Vol.56 No.6

The present investigation aims to study the role of Pr2O3 on the structural, physical, and radiation shielding properties of a dense cadmium lead borate glass. The XRD was used to affirm the glassy amorphous structure of fabricated sample materials. Moreover, the FTIR was used to record the change in the FT-IR spectra due to the addition of Pr2O3 in the wavenumber interval between 400 and 4000 cm 1. The features of glass surfaces and the elemental analyses for the synthesized Pr2O3-reinforced cadmium lead borate glasses were performed using a SEM, supported by an energy-dispersive spectrometer. The γ-ray protection capacity was evaluated using the Monte Carlo method in a wide energy interval ranging between 0.015 and 15 MeV. The linear attenuation coefficient (LAC) at 1 MeV was reduced by a factor of 10 % from 0.372 cm 1 to 0.340 cm 1. The decrease in the LAC values negatively affected the other shielding properties such as half-value thickness and the transmission factor. Although the linear attenuation coefficient is decreased slightly with the partial substitution of CdO by Pr2O3 compound, the fabricated glass samples still have a high shielding capacity compared to the traditional commercial glasses as well as previous similar reported glasses

Effects of voids and rotation on plane waves in generalized thermoelasticity

S. M. Abo-Dahab,A. M. Abd-Alla,S. R. Mahmoud 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.12

In the present paper, we study the influence of rotation, thermal and voids parameters on the reflection phenomenon of plane waves in generalized thermoelastic solid with one relaxation time. The governing field equations for isotropic and homogeneous thermoelastic half-space with voids and rotation are formulated in the context of Lord and Shulman theory of generalized thermoelasticity. The solutions of these governing equations indicate the existence of four coupled plane waves, namely; 1 P ;P 3 ;P and 4 P waves in the thermoelastic medium. The boundary conditions at stress-free thermally insulated surface are satisfied to obtain the system of four nonhomogenous equations in the reflection coefficients of various reflected waves for the incidence of 1 P wave. A particular material is modeled as the thermoelastic solid half-space to compute the complex absolute values of speeds and reflection coefficients. The speeds and reflection coefficients are shown graphically to observe the influences of rotation, thermal relaxation time and voids parameters.

Analytical solution of wave propagation in a non-homogeneous orthotropic rotating elastic media

A. M. Abd-Alla,S. R. Mahmoud 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.3

In this paper, the natural frequencies of the radial vibrations of a hollow cylinder and hollow sphere with different boundary conditions under influences of rotation and non-homogeneity have been studied. The radial vibrations of orthotropic material as affected by the angular velocity are investigated on the basis of the linear theory of elasticity. The of elastodynamic equations have been solved in analytical form. Numerical results are given and illustrated graphically for each case. Comparisons are made with previous results which given in the absence of rotation and non-homogeneity. The results indicate that the effect of rotation and non-homogeneity is very pronounced.

Impacts of siltstone rocks on the ordinary concrete's physical, mechanical and gamma-ray shielding properties: An experimental examination

Aita R.S.,Mahmoud K.A.,Ghany H.A. Abdel,Ibrahim E.M.,El-Feky M.G.,El Aassy I.E. 한국원자력학회 2024 Nuclear Engineering and Technology Vol.56 No.6

A series of ordinary concrete is casted in order to examine the influence of the manganiferous siltstone rocks on the physical, mechanical, and gamma-ray shielding properties. Thus, a partial replacement for the coarse aggregates by siltstone rocks was performed during the fabrication of the currently ordinary concrete. The test revealed that raising the siltstone concentration improved the mechanical characteristics and density of the developed concretes. The addition of siltstone rocks at concentrations ranging from 0 to 40 wt% of the coarse aggregate concentration raises the density of the concrete from 2.05 g/cm3 to 2.3 g/cm3. Furthermore, partial substitution of basalt with siltstone rocks improves gamma-ray shielding properties. The experimental results for the linear attenuation coefficient show an increase in its value from 0.146 cm1 to 0.160 cm 1 when the siltstone concentration is increased between 0 and 40 wt% at 0.662 MeV. Furthermore, increasing the concentrations of siltstone affected the half-value thickness, which varied between 4.759 and 4.319 cm at 0.662 MeV. Therefore, the replacement presents a new alternative coarse aggregate that can enhance the mechanical and radiation shielding properties of ordinary concretes.

Stability investigation of symmetrically porous advanced composites plates via a novel hyperbolic RPT

S. R. Mahmoud,E.I. Ghandourah,A.H. Algarni,M.A. Balubaid,Abdelouahed Tounsi,Abdeldjebbar Tounsi,Fouad Bourada 국제구조공학회 2023 Steel and Composite Structures, An International J Vol.46 No.4

This paper presents an analytical hyperbolic theory based on the refined shear deformation theory for mechanical stability analysis of the simply supported advanced composites plates (exponentially, sigmoidal and power-law graded) under triangular, trapezoidal and uniform uniaxial and biaxial loading. The developed model ensures the boundary condition of the zero transverse stresses at the top and bottom surfaces without using the correction factor as first order shear deformation theory. The mathematical formulation of displacement contains only four unknowns in which the transverse deflection is divided to shear and bending components. The current study includes the effect of the geometric imperfection of the material. The modeling of the micro-void presence in the structure is based on the both true and apparent density formulas in which the porosity will be dense in the mid-plane and zero in the upper and lower surfaces (free surface) according to a logarithmic function. The analytical solutions of the uniaxial and biaxial critical buckling load are determined by solving the differential equilibrium equations of the system with the help of the Navier’s method. The correctness and the effectiveness of the proposed HyRPT is confirmed by comparing the results with those found in the open literature which shows the high performance of this model to predict the stability characteristics of the FG structures employed in various fields. Several parametric analyses are performed to extract the most influenced parameters on the mechanical stability of this type of advanced composites plates.