Teleparallel Energy-momentum Distribution of Locally Rotationally Symmetric Spacetimes

M. Jamil Amir,Tahir Nazir 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.9

In this paper, we explore the energy-momentum distribution of locally rotationally symmetric(LRS) spacetimes in the context of the teleparallel theory of gravity by considering the three metrics,I, II and III, representing the whole class of LRS sapcetimes. In this regard, we use the teleparallelversions of the Einstein, Landau-Lifshitz, Bergmann-Thomson, and M¨oller prescriptions. Theresults show that the momentum density components for the Einstein, Bergmann-Thomson, andM¨oller prescriptions turn out to be same in all cases of the metrics I, II and III, but are differentfrom those of the Landau- Lifshitz prescription, while the energy components remain the same forthese three prescriptions only in all possible cases of the metrics I and II. We mention here thatthe M¨oller energy-momentum distribution is independent of the coupling constant ; that is, theseresults are valid for any teleparallel models.

Robust Unified Multi Diverse Protection Schemes for Low Voltage Microgrid

Khan Jamil Ahmad,Mahmood Tahir 대한전기학회 2024 Journal of Electrical Engineering & Technology Vol.19 No.2

A microgrid (MG) is characterized by an arrangement of renewable energy sources (RES) and loads connected together to the distribution system. With the high dispersion of distributed generations (DG) in microgrids, which is inevitable, the distribution system will experience diverse challenges not only in its performance but also in the protection set-up. The lack of a comprehensive applicable protection scheme, which must be attuned to islanded and grid-connected modes of microgrid operation, is a key problem. The problem becomes more challenging and complex in an islanded operation of a microgrid (MG) due to limited fault current contribution by inverter based DGs. Therefore, conventional protection strategies cannot be applied in a radial distribution system with DGs. The lack of comprehensive protection schemes, which must be attuned with islanded and grid-connected modes of microgrid operation, is a challenging task to be implemented. To grasp the superlative protection scheme for MGs, the combined action of diferent protection strategies is required. Extensive research on the development of MG protection strategies reveals their incompetency to cater for protection of every component of the entire microgrid in its prevailing conditions being employed in solo-mode and also that no scheme is able to work without communication assistance. The current work proposes the comprehensive implementation of communication-less unifed diverse protection schemes that include current diferential relays, directional and non-directional overcurrent conventional IEC (International Electrotechnical Commission) standard-based overcurrent relays, and novel non-standard voltage-current relays. The assembly and graphical representation of proposed relays for each scheme are developed in MATLAB/Simulink during the simulation. The accomplished results of these diverse protection schemes are validated through simulations applied to the benchmark microgrid system using an industrial software package called ETAP (Electrical Transient Analyzer Program).

Surface and Electronic Properties of Hydrogen Terminated Si [001] Nanowires

Matsuda, Yuki,Tahir-Kheli, Jamil,Goddard , William A. American Chemical Society 2011 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.115 No.25

<P>The calculated band gaps reported previously for silicon nanowires (SiNW) have disagreed with the experimental values both in magnitude and in the behavior with radius. We resolve this discrepancy here. We report ab initio quantum mechanical calculations of hydrogen terminated Si [001] nanowires (H–SiNWs) as a function of diameter (<I>d</I>) and hydrogen coverage using the B3LYP density functional. For smaller diameters (<I>d</I> ≤ 1.9 nm) we find that the most stable surface is fully saturated with hydrogen leading to direct band gaps. For larger diameters, the surface dangling bonds are not saturated, leading to surface LUMO and HOMO states that lower the gap and lead to an indirect band gap. This transition from direct to indirect gap resolves the previous disagreement in the scaling of band gap with diameter. We conclude that the electronic properties of Si NW depend sensitively on controlling the diameter and surface hydrogen coverage.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2010/jpccck.2010.115.issue-25/jp106048u/production/images/medium/jp-2010-06048u_0002.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp106048u'>ACS Electronic Supporting Info</A></P>

Synthesis and properties of aqueous polyurethane dispersions: Influence of molecular weight of polyethylene glycol

Mohammad Zuber,Fatima Mumtaz,Khalid Mahmood Zia,Tahir Jamil,Rizwan Hussain 한국화학공학회 2013 Korean Journal of Chemical Engineering Vol.30 No.12

Aqueous polyurethane dispersions (PUDs) have recently emerged as important alternatives to their solventbased counterparts for various applications due to increasing health and environmental awareness. A series of aqueous polyurethane dispersions containing carboxylate anion as hydrophilic pendant groups were synthesized through step growth polymerization reaction using hexamethylene diisocyanate (HDI), 1,4-butanediol (1,4-BDO), dimethylol propionic acid (DMPA) and polyethylene glycol (PEG) of different molecular weight. Effect of PEG molecular weight was investigated on molecular structure, contact angle measurement, and physical and adhesive properties of PU emulsions. Fourier transform infrared spectroscopy (FT-IR) was used to check the completion of polymerization reaction. Contact angle measurement indicated that the hydrophilicity of polymer increases by increasing molecular weight of PEG with a corresponding decrease in contact angle. Results of T-peel test showed a decrease in peel strength by increasing molecular weight of PEG. Moreover, solid contents%, drying time and storage stability suggested fast drying properties and greater stability of aqueous PU dispersions.

Synthesis and characterization of polyurethane/bentonite nanoclay based nanocomposites using toluene diisocyanate

Muhammad Fiayyaz,Khalid Mahmood Zia,Mohammad Zuber,Tahir Jamil,Muhammad Kaleem Khosa,Muhammad Asghar Jamal 한국화학공학회 2014 Korean Journal of Chemical Engineering Vol.31 No.4

Polyurethanes (PUs) prepolymers blended with bentonite nanoclay and without bentonite nanoclay wereprepared by the reaction of toluene-2,4-diisocyanate (TDI) and hydroxyl terminated polybutadiene (HTPB), and thechain was further extended with 1,4-butane diol (1,4-BDO) to get final polyurethane nanocomposites (PUNC). A mixtureof polymer and bentonite clay enriched in montmorillonite (MMT) was formed in solution polymerization, in whichMMT dispersed depending on interaction of MMT with polymer chains. The molecular structure of the monomersand the prepared PU nanocomposites was confirmed by FTIR. A series of PUNCs were prepared by varying the percentcompositions of bentonite nanoclay into the PU matrix. The existence of the clay in to the PU was confirmed byscanning electron microscope (SEM). SEM images verified the good dispersion of the bentonite nanoclay in PU matrix.

Mixed matrix membranes: Two step process modified with electrospun (carboxy methylcellulose sodium salt/sepiolite) fibers for nanofiltration

Maria Wasim,Aneela Sabir,Muhammad Shafiq,Atif Islam,Mudassar Azam,Tahir Jamil 한국공업화학회 2017 Journal of Industrial and Engineering Chemistry Vol.50 No.-

mixed matrix membrane (MMMs) was fabricated in two steps,first by formation of modified substrateand second is deposition of electrospunfibrous layer with varying sepiolite concentration fornanofiltration. MMM3 showed an optimal MgSO4 rejection of 97.6% with 40.8 L/m2 hflux whileMMM5 showed highest MgCl2 rejection of 96.95% withflux of 31 L/m2 h. The fouling data revealed thatmodified surface is effective in improving the antifouling property which caused decrease in theadsorption phenomena of microbes on to the surface. The antibacterial properties of the membranesshowed the inhibition of the growth of Escherichia coli.

Fabrication and performance characterization of novel zinc oxide filled cross-linked PVA/PEG 600 blended membranes for CO2/N2 separation

Muhammad Rizwan Dilshad,Atif Islam,Aneela Sabir,Muhammad Shafiq,Muhammad Taqi Zahid Butt,Aamir Ijaz,Tahir Jamil 한국공업화학회 2017 Journal of Industrial and Engineering Chemistry Vol.55 No.-

In this study zinc oxide filled and unfilled polyvinyl alcohol (PVA)/polyethylene glycol (PEG) 600 blended membranes with different degrees of cross-linking (mol%) were prepared using formaldehyde as a crosslinking agent and characterized by FTIR, SEM, TGA, mechanical analysis and permeation testing for CO2 and N2 gases. The effects of synthesis parameters like cross-linking ratio, wt.% PEG content and wt.% zinc oxide content on the membrane characteristics were also investigated. It was found that at 60 mol% degree of cross-linking and 60 wt.% PEG content, the membranes showed maximum CO2/N2 ideal selectivity of 26 and reasonable CO2 permeability of 52.9 Barrers at 25 C and 1.5 bar. It was also found that at 2 wt.% zinc oxide content, membranes showed highest CO2/N2 ideal selectivity of 112.8 and maximum CO2 permeability of 423 Barrers at 25 C and 1.5 bar.

Synthesis and characterization of polyurethane based on aliphatic diisocyanate and stiff chain extenders

Mohammad Zuber,Khalid Mahmood Zia,Muhammad Ashair Iqbal,Zahida Tariq Cheema,Muhammad Ishaq,Tahir Jamil 한국화학공학회 2015 Korean Journal of Chemical Engineering Vol.32 No.1

The present research work was performed to study the properties of polyurethanes (PU) based on ali-phatic diisocayanate and the effect of chemical structure of chain extenders. Two series of PUs were synthesized via twosteps polymerization technique. The PU samples constituted on hexamethylene diisocayanate (HDI), hydroxy-termi-nated polybutadiene (HTPB) and blends 1, 4 butanediol (BDO)/bisphenol A (BPA) and or 1, 4 butanediol (BDO)/bisphenol S (BPS) were prepared. Structural characterization was done using Fourier transform infrared spectroscopyduring and after the synthesis. The FTIR analysis confirmed the existence of proposed bisphenol A (BPA) and bisphe-nol S (BPS) based PU structures. Differential scanning calorimeter (DSC) analysis gives information about the thermaltransition of all the polymer samples. Because of the difference of polarity between hard and soft segments of PU,microphase separation can occur. The degree of phase separation in the prepared PU was confirmed using scanningelectron microscope (SEM) technique. The SEM techniques present a distinctive chance to directly visualize the mor-phology of the polyurethanes.