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1
Content available Numerical analysis of the compositional graded quaternary barrier AlGaN-based ultraviolet-C light-emitting diode
Malik S., Usman Muhammad, Hussain M., Munsif M., Khan S., Rasheed S., Ali S.
Opto-Electronics Review
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2021
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Vol. 29, No. 3
80--84
EN
The compositional graded quaternary barriers (GQBs) instead of ternary/conventional quantum barriers (QBs) have been used to numerically enhance the efficiency of AlGaN-based ultraviolet light-emitting diode (LED). The performance of LED with GQBs is examined through carrier concentrations, energy band diagrams, radiative recombination, electron and hole flux, internal quantum efficiency (IQE), and emission spectrum. As a function of the operating current density, a considerable reduction in efficiency droop is observed in the device with composition-graded quaternary barriers as compared to the conventional structure. The efficiency droop in case of a conventional LED is ~77% which decreased to ~33% in case of the proposed structure. Moreover, the concentration of electrons and holes across the active region in case of the proposed structure is increased to ~156% and ~44%, respectively.
2
Content available Characterization of the Hammamet basin aquifer (North-East of Algeria) through geochemical and geostructural methods and analysis
Chelih F., Fehdi C., Khan S.
Journal of Water and Land Development
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2018
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no. 37
39--48
EN
Morphostructural, hydrogeological and hydrochemical approaches were applied to Hammamet plain and its surrounding mountains in the eastern part of Algeria to characterize the groundwater system and its potential for exploitation. The Essen and Troubia Mountains form the natural boundaries of Hammamet plain. The objective of this study is to utilize remote sensing techniques combined with structural analysis, hydrogeology and hydrogeochemistry to identify the potential fracture zones for groundwater in the strongly fractured and karstified deep aquifers. The delineated zones of potential groundwater resources are verified by detailed hydrogeological field surveys. From a hydrogeological point of view, these two mountains, constitute a unit limited by faults oriented ENE-WSW, NNW-SSE and NNE-SSW. Specifically, fractures of the latter two directions influence the compartmentalization and the hydrogeological functioning of this unit. According to the degree of fracturing and/or karstification, two basic types of aquiferous behaviour have been distinguished: fissured aquifer (Essen Mountain and Troubia Mountain), and porous aquifer (Hammamet plain). The study of the hydrochemical characteristics of groundwater samples shows that the majority of samples are mainly of HCO3– and Ca2+ water type. The ionic speciation and mineral dissolution/precipitation was calculated with the PHREEQC software. The chemical composition of the water is influenced by the dissolution and/or precipitation processes during the water–rock interaction and by the cationic exchange reactions between groundwater and alluvial sediments. The high content of CO2 in the water samples suggests that they circulate in a geochemical open system. The isotopic analysis of some groundwater samples shows a similarity with the meteoric waters, which reflect their short residence time and a low evaporation of the infiltrated water.
PL
Celem scharakteryzowania systemu wód podziemnych oraz możliwości eksploatacji tych wód zastosowano metody morfologiczne, hydrogeologiczne i hydrochemiczne na równinie Hammamet i otaczających ją górach we wschodniej części Algierii. Góry Essen i Troubia tworzą naturalną granicę równiny Hammamet. Przedmiotem badań była identyfikacja możliwych stref szczelin w silnie spękanym i głębokim, krasowym poziomie wodonośnym z zastosowaniem technik teledetekcji w połączeniu z analizą strukturalną, hydrogeologią i hydrogeochemią. Wytyczone strefy potencjalnych zasobów wód gruntowych weryfikowano w szczegółowych hydrogeologicznych badaniach terenowych. Z hydrogeologicznego punktu widzenia wymienione góry stanowią jednostkę ograniczoną przez uskoki ułożone wzdłuż linii ENE-WSW, NNW-SSE i NNE-SSW. Szczeliny w dwóch ostatnich kierunkach wpływają na podział i hydrologię tej jednostki. Według stopnia spękania i/lub postępu procesów krasowych wyróżniono dwa główne typy poziomów wodonośnych: poziom spękany (góra Essen i góra Troubia) oraz poziom porowaty (równina Hammamet). Badanie hydrochemicznych właściwości próbek wody gruntowej wykazało, że są one zdominowane przez HCO3– i Ca+2. Skład jonowy i procesy rozpuszczania/wytrącania obliczano za pomocą programu PHREEQC. Na skład chemiczny wody wpływają procesy rozpuszczania i precypitacji w czasie oddziaływań między wodą a podłożem skalnym oraz wymiana kationów między wodą gruntową a aluwialnymi osadami. Duże stężenie CO2 w próbkach wody sugeruje, że krąży ona w systemie otwartym. Analiza izotopowa niektórych próbek wody wykazuje ich podobieństwo do wód opadowych, co uwidacznia się w ich krótkim czasie retencji i niewielkim parowaniu wód infiltracyjnych.
3
Content available Carbon emissions, energy use, gross domestic product and total population in China
Ahmad M., Hengyi H., Rahman Z. U., Khan Z. U., Khan S., Khan Z.
Ekonomia i Środowisko
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2018
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nr 2
32--44
EN
The current study explores the impact of energy consumption, total population, gross domestic product on carbon emissions by utilizing time series data of 1971-2013 for China. Earlier studies concentrated on testing the present form of an environmental Kuznets curve not taking total population in a model. Specifically, this study focuses on analyzing the long run existence of environmental Kuznets curve. The methodology of auto regressive distributed lag model is utilized. The quadratic linkage between national income and emissions of carbon have been detected, confirming the presence of long run linkage between quadratic national income and emissions of carbon. Granger causality test divulge one-way causality between gross domestic product and carbon emissions. The empirical findings also reveal that the energy use and national income are important factors of carbon emanations in the long run. Total population has an insignificant positive influence on emissions of carbon. It is suggested that government should focus to extract that substitute sources of energy which is more environmental friendly.
4
Content available remote Detection of ECG T-wave Alternans Using Maxima of Continuous-Time Wavelet Transform Ridges
Bakhshi A. D., Ahmed A., Gulfam S., Khaqan A., Yasin A., Riaz R., Alimgeer K., Malik S., Khan S., Dar A.H.
Przegląd Elektrotechniczny
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2012
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R. 88, nr 12b
35-38
EN
Prognostic utility of microvolt T-wave alternans (TWA) has been established since its clinical acceptance as marker for malignant ventricular arrhythmias, leading to sudden cardiac death. Accurate detection of TWA from surface ECG is a challenge because of invisible nature of the phenomenon. A novel TWA detection scheme based upon analysis of continuous time wavelet ridges (CTWR) of consecutive ventricular repolarization complexes is presented. The CTWR is computed using maxima of wavelet energy coefficients of continuous wavelet transform. Variety of simulated alternans waveforms, wavelet functions, frequency bands and noise levels are used to test the algorithm. The study concludes that CTWR can successfully characterize the alternation of cardiac repolarization and detect TWA phenomenon.
PL
Diagnostyka sygnału TWA odgrywa dużą rolę w badaniach jako marker arytmii powodującej zawał serca. Sygnał TWA jest wykrywany jako składowa sygnału elektrokardiogramu. W artykule opisano wykorzystanie ciągłej transformaty falkowej do analizy tego sygnału. (Detekcja składowej TWA sygnału EKG bazująca na wykorzystaniu ciągłej transformaty falkowej)
5
Content available remote Atmospheric influences on satellite communications
Zubair M., Haider Z., Khan S., Nasir J.
Przegląd Elektrotechniczny
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2011
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R. 87, nr 5
261-264
EN
Among other atmospheric regions, ionosphere, which is ionized region of the atmosphere, is considered to impose serious limitations on satellite communication. At higher frequencies, radio waves pass through the ionosphere and are attenuated due to the free electrons present in ionosphere. This paper discusses atmospheric effects on high frequency radio waves illustrating the attenuation and losses it may come across like attenuation due to atmospheric gases, rain, clouds, beam spreading loss and noise temperature. Data used to summarize the influence of atmospheric phenomena is obtained from ITU-R models and processed using MATLAB.
PL
Spośród różnych warstw atmosfery szczególnie jonosfera wpływa niekorzystnie na komunikację za pośrednictwem satelitów. Przy wyższych częstotliwościach fale radiowe są silnie tłumione w jonosferze. Artykuł przedstawia analizę wpływu czynników atmosferycznych w jonosferze na tłumienie i straty w radiowej komunikacji wysokoczęstotliwościowej.
6
Content available remote RP-HPLC analysis of withanolides in the flowers, leaves, and roots of Withania somnifera
Ali N. W, Abouzid S, Nasib A, Khan S., Qureshi J, Choudhary M. I
Acta Chromatographica
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2010
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Vol. 22, no. 3
473--480
EN
Ashwaghanda, Withania somnifera , is one of the most widely used herbs in Ayurvedic medicine. Leaves and roots are the traditionally used parts of the plant. An RP-HPLC method using a binary acetonitrile-water gradient containing 0.1% acetic acid has been developed for analysis of withaferin A. The method was validated in accordance with ICH guidelines and used for analysis of the withanolide content of the flowers, leaves, and roots of W. somnifera . The withanolide content was highest in the flowers.
7
Coumaroyl Adenosine and Lignan Glycoside from Amaranthus spinosus L
Azhar-ul-Haq, Malik A., Khan S., Muhammad P.
Polish Journal of Chemistry
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2006
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Vol. 80, nr 2
259-263
EN
Phytochemical investigation of the n-butanol fraction of the methanolic extract of the whole plant of Amaranthus spinosus Linn. led to the isolation of amaranthoside, a lignan glycoside 1, and amaricin, a coumaroyl adenosine 2 along with stigmasterol glycoside 3. The structures of these compounds were determined by spectral analysis (including 1Dand 2D-NMR experiments) and comparison with literature data.
8
Urease Inhibiting Guaianolides from Amberboa ramosa
Khan S., Riaz N., Afza N., Malik A., Azhar-ul-Haq, Ahmed Z., Lodhi M., Choudhary M.
Polish Journal of Chemistry
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2004
|
Vol.78 /nr 11-12
2075-2080
EN
New sesquiterpene lactones have been isolated from the chloroform-soluble fraction of Amberboa ramosa and assigned two structures 4 beta-(chloromethyl)-3 beta, 4 alfa-dihydroxy, 8alfa-[(s)-2-carboxypropionoxy]-1alfaH,5alfaH,6betaH,7alfaH-guaia-10(14),11(13)-dien- 6,12-olide (1) and 4 beta(chloromethyl)-3beta ,4alfa-dihydroxy,8alfa-[(s)-3-hydroxy-2-methylpropionyloxy]- 1alfaH,5alfaH,6beta H,7alfaH-guaia-10(14),11(13)-dien-6,12-olide (2), respectively. In addition 5-hydroxy-6-methyl-7-methoxyflavone (3), 6,2',5'-trihydroxy-3,5,7-trimethoxyflavone (4) and 5-hydroxy-3,7,8,2'-tetramethoxyflavone (5) have also been reported for the first time from this species. Compounds 1 and 2 displayed promising inhibitory potential against enzyme urease in a concentration-dependent fashion.
9
Flavonoid Glycoside and LOng Chain Ester from the Roots of Vitex negundo
ul-Haq A., Malik A., Khan S.
Polish Journal of Chemistry
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2004
|
Vol. 78 / nr 10
1851-1856
EN
Vitexoside, new flavonoid glycoside and hexatetracontanoic acid derivative have been isolated from the roots of Vitex negundo and assigned structures sakuranetin 4'-O(6"-O-alfa-L-rhamnopyranosyl)-beta-D-glucopyranoside 1 and 3-(3-methoxy-4-hydroxyphenyl) propyl hexatetracontanoate 2 respectively. In addition agnoside 3, 5-hydroxy- 1,3-benzenodicarboxylic acid 4, R-dalbergiphenol 5 and R-4-methoxy dalbergione 6 were also isolated for the first time from this species.
10
Content available remote Generating relations involving hypergeometric functions by means of integral operators
Pathan M., Khan S.
Demonstratio Mathematica
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2002
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Vol. 35, nr 1
35-39
EN
In this paper, the focus is on the results which involve exponential functions. The results of Pathan and Yasmeen [6] and Exton [3] are used with a view to obtaining generating functions which are partly unilateral and partly bilateral.
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