Controlling the length of plasma waveguide up to 5 mm, produced by femtosecond laser pulses in atomic clustered gas.

Mohamed, Walid Tawfik,Chen, Guanglong,Kim, Jaehoon,Tao, Geng Xiao,Ahn, Jungkwen,Kim, Dong Eon Optical Society of America 2011 Optics express Vol.19 No.17

<P>We report the observation of longitudinally uniform plasma waveguide with a controlled length of up to nearly 5 mm, in argon clustered gas jet. This self-channeling plasma is obtained using a 35 mJ, 30 fs FWHM pulse as a pump laser pulse to create the plasma channel. A 1 mJ pulse of the same laser is used for probing the plasma channels using interferometric diagnostics. The radial distribution of the electron density confirms the formation of a plasma waveguide. Clustered argon enhances the absorption efficiency of femtosecond pulses which enables the use of pump pulses of only 35 mJ, approximately 10 times less energy than required for heating conventional gas targets. The plasma channel length is controlled by the laser focus point (F), the laser intensity (I), the pump-probe delay time (t) and the laser height from a nozzle (z). The variation of the electron density for these parameters is also studied. We found that the highest density of 1.2 x 10(19) cm(-3) was obtained at I = 5.2 x 10(16) W/cm(2), z = 2 mm and t = 7.6 ns. It was demonstrated that by using a clustered jet, both the plasma waveguide length and the plasma density could be controlled.</P>

Double Boost Power-Decoupling Topology Suitable for Low-Voltage Photovoltaic Residential Applications Using Sliding-Mode Impedance-Shaping Controller

Tawfik, Mohamed Atef,Ahmed, Ashraf,Park, Joung-Hu The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.4

This paper proposes a practical sliding-mode controller design for shaping the impedances of cascaded boost-converter power decoupling circuits for reducing the second order harmonic ripple in photovoltaic (PV) current. The cascaded double-boost converter, when used as power decoupling circuit, has some advantages in terms of a high step-up voltage-ratio, a small number of switches and a better efficiency when compared to conventional topologies. From these features, it can be seen that this topology is suitable for residential (PV) rooftop systems. However, a robust controller design capable of rejecting double frequency inverter ripple from passing to the (PV) source is a challenge. The design constraints are related to the principle of the impedance-shaping technique to maximize the output impedance of the input-side boost converter, to block the double frequency PV current ripple component, and to prevent it from passing to the source without degrading the system dynamic responses. The design has a small recovery time in the presence of transients with a low overshoot or undershoot. Moreover, the proposed controller ensures that the ripple component swings freely within a voltage-gap between the (PV) and the DC-link voltages by the small capacitance of the auxiliary DC-link for electrolytic-capacitor elimination. The second boost controls the main DC-link voltage tightly within a satisfactory ripple range. The inverter controller performs maximum power point tracking (MPPT) for the input voltage source using ripple correlation control (RCC). The robustness of the proposed control was verified by varying system parameters under different load conditions. Finally, the proposed controller was verified by simulation and experimental results.

Double Boost Power-Decoupling Topology Suitable for Low-Voltage Photovoltaic Residential Applications Using Sliding-Mode Impedance-Shaping Controller

Mohamed Atef Tawfik,Ashraf Ahmed,박종후 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.4

This paper proposes a practical sliding-mode controller design for shaping the impedances of cascaded boost-converter powerdecoupling circuits for reducing the second order harmonic ripple in photovoltaic (PV) current. The cascaded double-boostconverter, when used as power decoupling circuit, has some advantages in terms of a high step-up voltage-ratio, a small numberof switches and a better efficiency when compared to conventional topologies. From these features, it can be seen that thistopology is suitable for residential (PV) rooftop systems. However, a robust controller design capable of rejecting double frequencyinverter ripple from passing to the (PV) source is a challenge. The design constraints are related to the principle of the impedanceshapingtechnique to maximize the output impedance of the input-side boost converter, to block the double frequency PV currentripple component, and to prevent it from passing to the source without degrading the system dynamic responses. The design hasa small recovery time in the presence of transients with a low overshoot or undershoot. Moreover, the proposed controllerensures that the ripple component swings freely within a voltage-gap between the (PV) and the DC-link voltages by the smallcapacitance of the auxiliary DC-link for electrolytic-capacitor elimination. The second boost controls the main DC-link voltagetightly within a satisfactory ripple range. The inverter controller performs maximum power point tracking (MPPT) for the inputvoltage source using ripple correlation control (RCC). The robustness of the proposed control was verified by varying systemparameters under different load conditions. Finally, the proposed controller was verified by simulation and experimental results.

Capacitor‑less modular multilevel converter with sliding mode control for MV adjustable‑speed motor drives

Mohamed Atef Tawfik,Mohammad Sameer Irfan,Chungu Lee,Ashraf Ahmed,Joung-Hu Park 전력전자학회 2022 JOURNAL OF POWER ELECTRONICS Vol.22 No.8

Medium-voltage (MV) motor drives have become an appealing application for modular multilevel converters (MMCs). Starting and operation at low speeds result in wide fluctuations of the low-frequency ripple components in the sub-module (SM) capacitors DC link voltages, which can adversely affect system performance and system lifetime. A solution for this problem is to replace the low-frequency (LF) SM capacitor with a power decoupling circuit (PDC) that is independent from the converter line frequency. In this paper, a power decoupling approach based on the flux cancelation method is proposed. A three-winding high-frequency transformer (HFT) is employed to magnetically couple and cancel the three-phase symmetrical ripple power. However, this approach has two main challenges. (1) The ripple powers through the HFT are a function of the value of the leakage inductances. (2) Different leakage inductances and ripple power unbalance between phases cause unequal ripple voltages. As a result, phase-shift ripple rejection control is needed. Conventional liner controllers have several problems, such as bandwidth limitations, stability margins, and slow dynamics near-zero-speed operation. In addition, linear controllers are designed for a specific ripple frequency. In this paper, a frequency-independent ripple rejection sliding mode controller (SMC) is proposed to overcome the limitations of linear controllers. The SMC is applied to pass the SM capacitor voltage ripple into the HFT. Thus, the ripple is canceled out in the HFT magnetic core regardless of the converter line frequency. The proposed control is suitable for adjustable-speed applications. The performance of the proposed scheme is verified via simulation and experimental tests.

Physical Activity and Cancer Prevention: Awareness and Meeting the Recommendations among Adult Saudis

Amin, Tarek Tawfik,Al-Hammam, Abudllah Mohammed,AlMulhim, Nasser Abdullah,Al-Hayan, Mohammed Ibrahim,Al-Mulhim, Mona Mohammed,Al-Mosabeh, Modhahir Jawad,Al-Subaie, Mohammed Ali,Al-Hmmad, Qassem Ahmed Asian Pacific Journal of Cancer Prevention 2014 Asian Pacific journal of cancer prevention Vol.15 No.6

Background: There is a scarcity of information about the proportion of the adult Saudi population that meet the recommended guidelines of physical activity (PA) to reduce cancer risk. Moreover, their awareness about the role of PA in cancer prevention is unclear. Objectives: This cross-sectional study aimed at estimating the proportion of adult Saudis meeting the PA guidelines, specifically those recommended by American Cancer Society (ACS) for cancer prevention, and to assess the public awareness about the role of PA in cancer prevention. Materials and Methods: Using a multistage sampling method, 2,127 adult Saudis of both genders were recruited from 6 urban and 4 rural primary health care centers in Al Hassa, Saudi Arabia. Participants were personally interviewed to gather information about their sociodemographic characteristics, searching activity about PA and cancer, and the time spent in leisure time PA (moderate and vigorous)/week using the Global Physical Activity Questionnaire with show cards. Finally, items about the role of PA in cancer risk reduction were inquired. Results: Of the included participants, 11.6% met the recommendations for cancer prevention (${\geq}45$ minutes of moderate-vigorous PA activity/${\geq}5$ days/week or 225 minutes/week). Multivariate regression showed that being male (AOR=1.49, CI=1.09-2.06), <20 years of age (AOR=3.11, CI=2.03-4.76), and unemployed (AOR=2.22, CI=1.57-3.18) were significant predictors for meeting PA recommendations for cancer prevention. Only 11.4% of the sample indicated correctly the frequency and duration of PA required for an average adult to be physically active and while >70% of them indicated the role of PA in prevention of hypertension, coronary heart disease and lowering elevated blood cholesterol, only 18.6% and 21.7% correctly mentioned the role of PA in reducing colon and breast cancer risk, respectively. Poor knowledge was found among those with less than college education and aged ${\geq}50$ years. The level of knowledge was significantly positively correlated with total leisure time PA of the participants. Conclusions: A minority of adult Saudis in Al Hassa was aware about the role of PA in cancer prevention and engaged in sufficient LTPA for cancer risk reduction benefits, highlighting the need for public health actions to include policies and programs that address factors deterring their participation in LTPA and increasing their awareness with remedies to manage the prevalent misconceptions.

Synthesis, characterization, surface and biocidal effect of some germinate nonionic surfactants

Mohamed F. Zaky,Ismail A. Aiad,AHMED SALAH MAHMOUD TAWFIK 한국공업화학회 2015 Journal of Industrial and Engineering Chemistry Vol.21 No.1

Different fatty acid namely; palmitic, stearic, oleic and linoleic acids and polyethylene glycol-600 werereacted to give nonionic surfactants. The formed nonionic surfactants were reacted with germaniumdioxide in presence of sodium carbonate to form germinates nonionic surfactants (I, II, III, and IV). Thechemical structures of the synthesized surfactants were characterized by FT-IR and 1H-NMR spectra. Thesynthesized surfactants showed higher surface activity at different temperature and surface parametersinfluenced by chemical structure of surfactants. The thermodynamic calculations showed thatadsorption and micellization processes are spontaneous. The synthesized surfactants showed goodantimicrobial activities against the tested microorganisms including Gram positive, Gram negative aswell as fungi. The promising inhibition efficiency of these compounds against the sulfate reducingbacteria facilitates them to be applicable in the petroleum field as new categories of sulfate reducingbacteria biocides.

Upconversion Nanohybrid-Based Fluorescent Probe for The Detection of an Organic Pollutant in The Environmental Water

Mohamed R. Elmasry,Salah M. Tawfik,Yong-Ill Lee 한국분석과학회 2019 학술대회논문집 Vol.2019 No.11

Influence of thiourea synthesis with silica fume on the corrosion rate of reinforcement concrete

Tawfik Taher A.,El-Yamani Magdy A.,Serag Faried A.,Mohammed Shimaa M.,AbdEl-Hafez Gh.M. 한국자원공학회 2020 Geosystem engineering Vol.23 No.3

The examination of corrosion rate for steel reinforcement existent in concrete was carried out in the presence of silica fume and thiourea. The ordinary Portland cement (OPC) replacement was conducted with silica fume material at 5 and 10% by cement weight for concrete production, in addition to that using various percentage of thiourea (1, 2, 3 4 and 5%) added to concrete. Monitoring and estimating the corrosion rate for reinforcing steel existent in concrete with and without silica fume and thiourea was held with the usage of corrosion test cell. Besides, compressive and splitting tensile strength submerged in fresh and salty water of hardened concrete with and without silica fume and thiourea that were considered in the study. The immersion for all the samples of steel reinforcement with salty water (tap water with 1.5% of calcium sulphate and 3% of sodium chloride) for about 90 days of exposure were studied. The best results for the lowest corrosion rate were obtained when a mixture of silica fume with thiourea is used with concentrations of 10 and 3%, respectively compared with the ordinary concrete.

Intrauterine diabetic milieu instigates dysregulated adipocytokines production in F1 offspring

( Shady H. Tawfik ),( Maha M. Haiba ),( Mohamed I. Saad ),( Taha M. Abdelkhalek ),( Mervat Y. Hanafi ),( Maher A. Kamel ) 한국동물자원과학회(구 한국축산학회) 2017 한국축산학회지 Vol.59 No.1

Background: Intrauterine environment plays a pivotal role in the origin of fatal diseases such as the metabolic syndrome. Diabetes is associated with low-grade inflammatory state and dysregulated adipokines production. The aim of this study is to investigate the effect of maternal diabetes on adipocytokines (adiponectin, leptin and TNF-α) production in F1 offspring in rats. Methods: The offspring groups were as follows: F1 offspring of control mothers under control diet (CD) (CF1-CD), F1 offspring of control mothers under high caloric diet (HCD) (CF1-HCD), F1 offspring of diabetic mothers under CD (DF1-CD), and F1 offspring of diabetic mothers under HCD (DF1-HCD). Every 5 weeks post-natal, 10 pups of each subgroup were culled to obtain blood samples for biochemical analysis. Results: The results indicate that DF1-CD and DF1-HCD groups exhibited hyperinsulinemia, dyslipidemia, insulin resistance and impaired glucose homeostasis compared to CF1-CD (p > 0.05). DF1-CD and DF1-HCD groups had high hepatic and muscular depositions of TGs. The significant elevated NEFA level only appeared in offspring of diabetic mothers that was fed HCD. DF1-CD and DF1-HCD groups demonstrated low serum levels of adiponectin, high levels of leptin, and elevated levels of TNF-α compared to CF1-CD (p > 0.05). These results reveal the disturbed metabolic lipid profile of offspring of diabetic mothers and could guide further characterization of the mechanisms involved. Conclusion: Dysregulated adipocytokines production could be a possible mechanism for the transgenerational transmittance of diabetes, especially following a postnatal diabetogenic environment. Moreover, the exacerbating effects of postnatal HCD on NEFA in rats might be prone to adipcytokine dysregulation. Furthermore, dysregulation of serum adipokines is a prevalent consequence of maternal diabetes and could guide further investigations to predict the development of metabolic disturbances.

Profile of Non-Communicable Disease Risk Factors Among Employees at a Saudi University

Amin, Tarek Tawfik,Al Sultan, Ali Ibrahim,Mostafa, Ola Abdelmoniem,Darwish, Amr Ahmed,Al-Naboli, Mohamed Rashad Asian Pacific Journal of Cancer Prevention 2014 Asian Pacific journal of cancer prevention Vol.15 No.18

Background: There is paucity of studies defining the prevalence of non-communicable disease (NCD) risk factors in Saudi Arabia despite the surging epidemic of obesity, change in dietary habits and sedentary lifestyle. Objectives: This cross-sectional study aimed to assess the prevalence of NCDs risk factors among employees at King Faisal University in Al Hassa, Saudi Arabia and to determine the possible correlates for clustering of NCDs risk factors among them. Materials and Methods: All employees were invited to participate; the World Health Organization STEPwise approach was used for data collection which consisted of a personal interview to collect socio-demographic characteristics, NCD history, tobacco use, vegetables and fruit consumption, and physical activity (PA), followed by anthropometric measurements namely weight, height and waist circumference and blood pressure measurements, subjects were finally subjected to biochemical tests with determination of fasting plasma glucose, serum triglycerides, cholesterol and high density lipoproteins. Results: Of the surveyed employees (n=691), daily current smokers accounted for 22.7%. 94.9%, 95.1% and 86% consumed < 5 servings per day of vegetables, fruits and both fruits and vegetables respectively, 73% were physically inactive, 64% were overweight or obese, 22.1% had hypertension, and 21.5% were diabetics. Elevated cholesterol levels were found in 36.6%, low high density lipoproteins in 36.8%, and elevated triglycerides in 36.1%. Only 3% had no NCD risk factors, and 57.6% had ${\geq}3$ factors. Multivariate logistic regression showed that gender (being male, adjusted odds ratio 'aOR'=1.51), aged ${\geq}50$ years (aOR=3.06), < college education (aOR=1.75), current smokers (aOR=2.37), being obese (aOR=6.96) and having a low PA level (aOR=4.59) were the significant positive predictors for clustering of NCD risk factors. Conclusions: Over fifty percent of the studied university's employees had multiple (${\geq}3$) NCD risk factors. Screening and health promotion initiatives should be launched at least targeting the modifiable factors to avert the excessive risk for cardiovascular disease, diabetes mellitus and several types of cancers.