A Sweep-Line Algorithm and Its Application to Spiral Pocketing

EL-Midany, Tawfik T.,Elkeran, Ahmed,Tawfik, Hamdy Society for Computational Design and Engineering 2002 International Journal of CAD/CAM Vol.2 No.1

This paper presents an efficient line-offset algorithm for general polygonal shapes with islands. A developed sweep-line algorithm (SL) is introduced to find all self-intersection points accurately and quickly. The previous work is limited to handle polygons that having no line-segments in parallel to sweep-line directions. The proposed algorithm has been implemented in Visual C++ and applied to offset point sequence curves, which contain several islands.

An Efficient No-Core Cut Pocketing CAM System for Wire-EDM

EL-Midany, Tawfik T.,Kohail, Ahmed M.,Tawfik, Hamdy Society for Computational Design and Engineering 2006 International Journal of CAD/CAM Vol.6 No.1

Recently, wire-EDM became a necessity for many engineering applications, particularly in the dies making. No-Core cut process is helpful for operations in which falling slug can jam the machine or wire. In this paper a proposed CAM system (called NCPP) is introduced, to overcome the limitations of the existing CAM systems in the machining of No-Core cut. The proposed CAM system (NCPP) provides pocketing of No-core cut and optimal selection of the position of starting hole (wire threading point), to minimize toolpath length. It was written for data exchange between CAD-CAM-CNC machines. This data model will become part of the ISO (Data model for Computerized Numerical Controllers) international standard. The NCPP system has been implemented in Visual C++. Many examples are used to illustrate NCPP system. The results show that, NCPP saves the machining time by significant value. This value depends on the shape and complexity of the workpiece that is being cut.

A New Algorithm to Calculate the Optimal Inclination Angle for Filling of Plunge-milling

Tawfik, Hamdy Society for Computational Design and Engineering 2006 International Journal of CAD/CAM Vol.6 No.1

Plunge milling is the fastest way to mill away large volumes of metal in the axial direction. The residual volume (inaccessible volume by the plungers) is minimized when selecting a specific direction of filling. This direction is known as the optimal inclination angle for filling of the plunged area. This paper proposes a new algorithm to calculate the optimal inclination angle of filling and to fill the plunged area with multi-plungers sizes. The proposed algorithm uses the geometry of the 2D area of the shape that being cutting to estimate the optimal inclination angle of filling. It is found that, the optimal inclination angle for filling of the plunged area is the same direction as the longer width of the equivalent convex polygon of the boundary contour. The results of the tested examples show that, the residual volume is minimized when comparing the proposed algorithm with the previous method.

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.

Electroreflectance spectroscopy of compressively strained InGaN/GaN multi-quantum well structures

Tawfik, W.Z.,Ryu, H.Y.,Lee, J.K. Elsevier 2014 CURRENT APPLIED PHYSICS Vol.14 No.11

The built-in piezoelectric field induced by compressive stress in InGaN/GaN multi-quantum well (MQW) light-emitting diodes (LEDs) was investigated using the electric field dependent electroreflectance (ER) spectroscopic method. InGaN/GaN MQW structures were prepared on sapphire substrates of different thicknesses. Thinning the sapphire substrate enables control of the compressive stress by changing the curvature of the wafer bowing. The wafer bowing-induced mechanical stress alters the piezoelectric field in the InGaN/GaN MQW. The flat band voltage, estimated by measuring the applied reverse bias voltage that induces a 180<SUP>o</SUP> phase shift in the ER spectra, was decreased from -11.21 V to -10.51 V by thinning the sapphire substrate thickness from 200 to 60 μm. To calculate the piezoelectric field (F<SUB>pz</SUB>) from the compensation voltage, the depletion width was obtained from the capacitance-voltage measurement. The F<SUB>pz</SUB> estimated from the energy shift in ER peak in a bias range from 0 to -12 V was changed by 110 kV/cm.

Numerical Analysis of the Temperature Impact on Performance of GaN-Based 460-nm Light-Emitting Diode

Tawfik, Wael Z.,Lee, June Key American Scientific Publishers 2018 Journal of Nanoscience and Nanotechnology Vol.18 No.3

<P>The influence of temperature on the characteristics of a GaN-based 460-nm light-emitting diode (LED) prepared on sapphire substrate was simulated using the SiLENSe and SpeCLED software programs. High temperatures impose negative effects on the performance of GaN-based LEDs. As the temperature increases, electrons acquire higher thermal energies, and therefore LEDs may suffer more from high-current loss mechanisms, which in turn causes a reduction in the radiative recombination rate in the active region. The internal quantum efficiency was reduced by about 24% at a current density of 35 A/cm(2), and the electroluminescence spectral peak wavelength was red-shifted. The LED operated at 260 K and exhibited its highest light output power of similar to 317.5 mW at a maximum injection current of 350 mA, compared to 212.2 mW for an LED operated at 400 K. However, increasing temperature does not cause a droop in efficiency under high injection conditions. The peak efficiency at 1 mA of injection current decreases more rapidly by similar to 15% with increasing temperature from 260 to 400 K than the efficiency at high injection current of 350 mA by similar to 11%.</P>

Stress-induced piezoelectric field in GaN-based 450-nm light-emitting diodes

Tawfik, Wael Z.,Hyeon, Gil Yong,Lee, June Key American Institute of Physics 2014 JOURNAL OF APPLIED PHYSICS - Vol.116 No.16

Role of expanded clay aggregate, metakaolin and silica fume on the of modified lightweight concrete properties

Tawfik Taher A.,AlSaffar Doha M.,Tayeh Bassam A.,Metwally Khaled Ali,ElKattan Ibrahim M. 한국자원공학회 2021 Geosystem engineering Vol.24 No.3

This investigation aimed to assess the effect of micro-cementitious materials on the mechanical properties and sulphate resistance of modified eco-efficient lightweight concrete (MDLWC). A modified lightweight concrete (MDLWC) was produced by mixing Light-expanded clay aggregate (LECA) with normal coarse aggregate (dolomite cushed rock). The impact of using different percentage of micro-cementitious materials which was micro silica fume (5–20%) and metakaolin(10–35%) on the mechanical properties (compressive strength, splitting tensile and flexural strength), waves transmission velocity of the ultrasonic pulses and sulphate resistivity of MDLWC was studied. The overall results illustrated that the use of micro-cementitious materials in MDLWC caused an enhancement on MDLWC properties. However, the MDLWC specimens containing micro silica fume showed better results than metakaolin. The best results were observed while using samples containing 10% micro silica fume and 30 % metakaolin individually or combined. In addition, the usage of combined mixture of 10% micro silica fume and 30% metakaolin MDLWC mix showed the best improvement rate in compressive, splitting tensile and flexural strengths by 25, 53.3 and 66.6%, respectively, compared to control MDLWC specimens. On the other hand, the direct empirical equations were proposed on the basis of strong and nonlinear regression analysis using the test data to predict the mechanical properties of MDLWC relationships, rationally. Experimental tests were conducted on ultrasonic pulses velocity, which showed good correlation equation strength of MDLWC. Scanning electron microscopy illustrated that the pores of concrete is smaller for SF and MK individually or combined with MDLWC compared to the control concrete, demonstrating an enhancement within the interfacial microstructure with the pozzolanas incorporation. The previous difference could be explained due to the concrete strength and sulphate penetrability to an extent.

Novel <i>“</i>turn off-on<i>”</i> sensors for highly selective and sensitive detection of spermine based on heparin-quenching of fluorescence CdTe quantum dots-coated amphiphilic thiophene copolymers

Tawfik, Salah M.,Shim, Jimin,Biechele-Speziale, Dana,Sharipov, Mirkomil,Lee, Yong-Ill Elsevier Sequoia 2018 Sensors and actuators. B Chemical Vol.257 No.-

<P><B>Abstract</B></P> <P>Novel “turn off-on” optosensors based on amphiphilic thiophene copolymers coated CdTe quantum dots (P1QDs and P2QDs) were developed for the dual detection of heparin and spermine. The emission of the P1QDs and P2QDs is found to be quenched in the presence of heparin by electron transfer mechanism through electrostatic and hydrogen bonding interactions. Upon the addition of spermine, heparin has been removed from the surface of P1QDs and P2QDs due to the strong electrostatic interactions between spermine and heparin, which showed significant fluorescence recovery of the sensors. Under optimum conditions, both P1QDs and P2QDs sensors displayed excellent limits of detection for heparin of 1.59nmolL<SUP>−1</SUP> (R<SUP>2</SUP> =0.9955) and 0.88nmolL<SUP>−1</SUP> (R<SUP>2</SUP> =0.9908) with linear ranges of 1–11μmolL<SUP>−1</SUP> and 1–10μmolL<SUP>−1</SUP>, respectively. P1QDs and P2QDs also showed remarkable limits of detection for spermine of 2.90nmolL<SUP>−1</SUP> (R<SUP>2</SUP> =0.9957) and 1.66nmolL<SUP>−1</SUP> (R<SUP>2</SUP> =0.9928) with linear ranges of 0.05–15μmolL<SUP>−1</SUP> and 1–12μmolL<SUP>−1</SUP>, respectively. The P1QDs and P2QDs sensors show a high selectivity to heparin and spermine over common interfering substances and ions. In addition, the proposed method was successfully utilized in serum samples, which could facilitate the further heparin and spermine biochemical and biomedical research.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Novel CdTe QDs coated with amphiphilic conjugated polythiophenes were developed. </LI> <LI> Highly fluorescent P1QDs and P2QDs (QY, 63% and 78%) were used as “turn off–on” sensors. </LI> <LI> The sensors show highly selective and sensitive responses to heparin and spermine. </LI> <LI> The sensors were successfully applied to detect heparin and spermine in human serum. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Metal-organic framework films functionalized with nonionic conjugated polythiophenes for visual detection of PAHs

Tawfik, Salah M.,Lee, Yong-Ill Techno-Press 2021 Advances in nano research Vol.11 No.5

Natural and anthropogenic activities lead to the generation of polycyclic aromatic hydrocarbons (PAHs), persistent contaminants that adversely affect the environment and public health. However, highly sensitive, fast, and portable techniques for the detection of PAHs remain a technological challenge. The rapid analysis of urinary levels of 1-hydroxypyrene (1-HP) would enable PAH carcinogens to be measured using biomonitoring techniques. Here, we demonstrate biocompatible, easy-to-use, and portable sensors based on novel π-conjugated metal-organic frameworks (MOFs) for the detection of 1-HP. These sensors were developed by incorporating nonionic conjugated polythiophenes with a PLQY as high as 65% into lanthanide-MOFs (CP1-Eu-MOF and CP2-Eu-MOF) using an in-situ synthesis strategy. The emission of the sensors can be effectively quenched by 1-HP via hydrophobic, π-π stacking, and hydrogen bonding interactions. Significantly, the unique structure of CP2-Eu-MOF sensor displays superior performance with enhanced sensitivity (LOD ~1.02 pM) that is 1.63 times higher than that of CP1-Eu-MOF (LOD ~1.66 pM). More importantly, we successfully demonstrated the possibility of employing wax-printed paper in combination with a fast and cost-effective smartphone for rapid 1-HP detection. Moreover, portable sensory films were fabricated by incorporating CP2-Eu-MOF into a poly(vinylidene difluoride) (PVDF) matrix to produce CP2-Eu-MOF/PVDF films for the visual detection of 1-HP levels as low as 25 pM. Finally, the feasibility of successfully analyzing the levels of 1-HP in urine was verified by testing real urine samples with satisfactory recoveries of 94.1-103.5%. This method provides new pathways for the biomonitoring of polyaromatic environmental pollutants.