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Wyświetlanie 1-15 z 16
Tytuł:
Future applications of apricot (Prunus armeniaca kaisa) ß galactosidase in dairy industry
Autorzy:
Ansarin, S. A
Satar, R.
Zaidi, S. K.
Khan, M. J.
Naseer, M. I.
Al-Qahtani, M. H.
Maskat, M. Y.
Powiązania:
https://bibliotekanauki.pl/articles/779412.pdf
Data publikacji:
2014
Wydawca:
Zachodniopomorski Uniwersytet Technologiczny w Szczecinie. Wydawnictwo Uczelniane ZUT w Szczecinie
Tematy:
apricot
β galactosidase
lactose hydrolysis
dairy industries
Opis:
The present study demonstrates the immobilization of β galactosidase from apricots (Prunus armeniaca kaisa) on an inexpensive concanavalin A layered cellulose-alginate hybrid gel. Immobilized β galactosidase retained 78% of the initial activity after crosslinking by glutaraldehyde. It exhibited greater fraction of activity at both acidic and basic pH, and showed broad spectrum temperature optimum as compared to free enzyme. Moreover, immobilized enzyme exhibited higher thermal stability at 60oC and retained 80% of the original enzyme activity in presence of 3% galactose. The crosslinked immobilized enzyme showed improved hydrolysis of lactose from milk and whey in batch processes at 50oC as well as in continuous reactors operated at flow rate of 20 mL/h and 30 mL/h even after one month. Moreover, crosslinked adsorbed β galactosidase retained 76% activity even after its sixth repeated use, thereby promoting its use for lactose hydrolysis in various dairy products even for longer durations.
Źródło:
Polish Journal of Chemical Technology; 2014, 16, 3; 74-79
1509-8117
1899-4741
Pojawia się w:
Polish Journal of Chemical Technology
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Significant Influence of Annealing Temperature and Thickness of Electrode on Energy Conversion Efficiency of Dye Sensitized Solar Cell: Effect of Catalyst
Autorzy:
Uddin, J.
Islam, J. M. M.
Khan, S. M. M.
Hoque, E.
Khan, M. A.
Powiązania:
https://bibliotekanauki.pl/articles/412298.pdf
Data publikacji:
2014
Wydawca:
Przedsiębiorstwo Wydawnictw Naukowych Darwin / Scientific Publishing House DARWIN
Tematy:
Dye Sensitized Solar Cell
sensitizer
catalyst
annealing temperature
thickness
Opis:
Dye sensitized solar cell (DSSC) shows great promise as an alternative to conventional p-n junction solar cells due to their low fabrication cost and reasonably high efficiency. DSSC was assembled by using natural dye extracted from red amaranth (Amaranthus Gangeticus) as a sensitizer and different catalysts for counter electrode were applied for maximum energy conversion efficiency. Annealing temperature and thickness of electrode were also investigated and optimized. Catalyst, annealing temperature and thickness were optimized by the determination of cell performance considering photoelectrochemical output and measuring current and voltage; then calculating efficiency and other electrical parameters. The experimental results indicated that samples having 40 μm electrode thickness and prepared at 450 o C annealing temperature showed the best performance.
Źródło:
International Letters of Chemistry, Physics and Astronomy; 2014, 20, 1; 78-87
2299-3843
Pojawia się w:
International Letters of Chemistry, Physics and Astronomy
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Performance Evaluation of Cognitive Radio Network Based on 2-D Markov Chain
Autorzy:
Islam, M. I.
Rabbi, M. F.
Khan, R. T.
Akhter, J.
Powiązania:
https://bibliotekanauki.pl/articles/958115.pdf
Data publikacji:
2015
Wydawca:
Instytut Łączności - Państwowy Instytut Badawczy
Tematy:
cognitive radio networks
misdetection
probability of false alarm
throughput and traffic of limited channel
Opis:
The objective of cognitive radio network is to enhance the wireless network spectrum utilization. In such a network, two types of users are enlisted, namely primary user (PU) and secondary user (SU). The PU can access any channel in case of its availability, but SU users have lower priority and can access a channel only when it is unused by PUs. The performance of such a network solely depends on two traffic parameters: probability of false alarm and probability of misdetection. In this paper the performance of such a network is analyzed based on two dimensional Markov chain including those parameters. The main contribution of this paper is to evaluate blocking probability and PU and SU throughput using the state transition chain instead of existing statistical analysis.
Źródło:
Journal of Telecommunications and Information Technology; 2015, 3; 39-44
1509-4553
1899-8852
Pojawia się w:
Journal of Telecommunications and Information Technology
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Comparative efficacy of silymarin and choline chloride (liver tonics) in preventing the effects of aflatoxin B1 in bovine calves
Autorzy:
Naseer, O.
Khan, J.A.
Khan, M.S.
Omer, M.O.
Chishti, G.A.
Sohail, M.L.
Saleem, M.U.
Powiązania:
https://bibliotekanauki.pl/articles/31837.pdf
Data publikacji:
2016
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Opis:
Aflatoxins are secondary metabolites produced by Aspergillus spp. which are injurious to animals and humans The aim of this study was to determine the effects of aflatoxin B1 (AFB1) on Average Daily Feed Intake (ADFI), Average Daily Weight Gain (ADWG), haematological and serum biochemical responses of Bovine Calves and to determine the comparative efficacy of two different liver tonics against AFB1. Twenty seven calves were selected from herd and divided into 3 groups. All calves were fed with 1.0 mg/kg AFB1 for a period of 10 days. After that they were fed with liver tonics: Silymarin fed at a rate of 600 mg/kg and Choline chloride 500 mg/kg for 7 days. The results indicate that the ADFI and ADWG of AFB1 treated calves decreased significantly. Serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), blood urea nitrogen (BUN) and creatinine significantly increased due to AFB1. In haematology the total erythrocyte count (TEC), total leukocyte count (TLC), haemoglobin concentration (HGB), haematocrit levels (HCT), mean corpuscular haemoglobin (MCH), mean corpuscular volume (MCV) and mean corpuscular haemoglobin concentration (MCHC), lymphocyte %, neutrophil % and monocyte % significantly decreased in AFB1 treated calves after 10 days of feeding. Both liver tonics significantly (p<0.05) improved all the parameters, including ADFI, ADWG, hematologial and serum biochemical test. However, Silymarin comparatively more efficiently ameliorate the effects induced by AFB1 than choline chloride.
Źródło:
Polish Journal of Veterinary Sciences; 2016, 19, 3
1505-1773
Pojawia się w:
Polish Journal of Veterinary Sciences
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Performance evaluation of ZVS/ZCS high efficiency AC/DC converter for high power applications
Autorzy:
Ali, A.
Chuanwen, J.
Khan, M. M.
Habib, S.
Ali, Y.
Powiązania:
https://bibliotekanauki.pl/articles/200472.pdf
Data publikacji:
2020
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
switching losses
zero current switching
zero voltage switching
power quality
reverse recovery loss
Opis:
The increased power density, reduced switching losses with minimum electromagnetic interference (EMI), and high efficiency are essential requirements of power converters. To achieve these characteristics, soft power converters employing soft switching techniques are indispensable. In this paper, a ZCS/ZVS PWM AC/DC converter topology has been emphasized, which finds applications in high power systems such as automobile battery charging and renewable energy systems. This converter scheme maintains zero current and zero voltage switching conditions at turn on and turn off moments of semiconductor switches, respectively and soft operation of rectifier diodes that lead to negligible switching and diode reverse recovery losses. Moreover, it improves power quality and presents high input power factor, low total harmonic distortion of the input current (THDI ) and improved efficiency. The validity of theoretical analysis of the proposed converter has been carried out experimentally on a 10 kW laboratory prototype. Experimental results prove that the soft switching operation of the semiconductor switches and diodes is maintained at 98.6% rated load efficiency. In addition, the performance evaluation has been performed by comparative analysis of the proposed converter with some prior art high power AC/DC converters. Efficiencies of the proposed and prior art high power topologies have been determined for different load conditions. The highest efficiency, power factor and lower THDI of the proposed converter topology complies with international standards.
Źródło:
Bulletin of the Polish Academy of Sciences. Technical Sciences; 2020, 68, 4; 793-807
0239-7528
Pojawia się w:
Bulletin of the Polish Academy of Sciences. Technical Sciences
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
A mixed control chart adapted to the truncated life test based on the Weibull distribution
Autorzy:
Khan, N.
Aslam, M.
Kim, K.-J.
Jun, C. -H.
Powiązania:
https://bibliotekanauki.pl/articles/406432.pdf
Data publikacji:
2017
Wydawca:
Politechnika Wrocławska. Oficyna Wydawnicza Politechniki Wrocławskiej
Tematy:
life test
Weibull distribution
attribute chart
binomial distribution
average run length
Opis:
The design of a new mixed attribute control chart adapted to a truncated life test has been pre-sented. It was assumed that the lifetime of a product follows the Weibull distribution and the number of failures was observed using a truncated life test, where the test duration was specified as a fraction of the mean lifespan. The proposed control chart consists of two pairs of control limits based on a binomial distribution and one lower bound. The average run length of the chart was determined for various levels of shift constants and specified parameters. The efficiency of the chart is compared with an existing control chart in terms of the average run length. The application of the proposed chart is discussed with the aid of a simulation study.
Źródło:
Operations Research and Decisions; 2017, 27, 1; 43-55
2081-8858
2391-6060
Pojawia się w:
Operations Research and Decisions
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Thermal Properties of Carbon Nanotube (CNT) Reinforced Polyvinyl Alcohol (PVA) Composites
Autorzy:
Hasan, M.
Das, S. K.
Islam, J. M. M.
Gafur, Md. A.
Hoque, E
Khan, M. A.
Powiązania:
https://bibliotekanauki.pl/articles/411675.pdf
Data publikacji:
2013
Wydawca:
Przedsiębiorstwo Wydawnictw Naukowych Darwin / Scientific Publishing House DARWIN
Tematy:
CNT
PVA
composite
Thermal properties
Gum acacia
Opis:
Homogeneous Polyvinyl alcohol (PVA)/Carbon nanotube (CNT) composite has been prepared by solution casting method using gum acacia as a surfactant. CNT content in the composite was varied from 5-10 % by weight. The thermal properties of PVA/CNT composites were investigated by Thermo Gravimetric/Differential Thermal Analyzer (TG/DTA) and Thermo Mechanical Analyzer (TMA). TG/DTA results showed that higher thermal stability in higher percentage of CNT in the composites. The 10 % CNT containing PVA composite exhibit highest onset of melting, glass transition point and offset of melting temperature and the recoded values are 330.4K, 379K and 421.3K respectively. All of the result indicates that the developed PVA/CNT composite might be promising for use in solar cell application.
Źródło:
International Letters of Chemistry, Physics and Astronomy; 2013, 12; 59-66
2299-3843
Pojawia się w:
International Letters of Chemistry, Physics and Astronomy
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Assessing Machinability and Surface Characteristics of a Shape Memory Alloy (SMA) Processed through Wire Electro Spark Erosion Method
Autorzy:
Ebenezer, George
Khan, Adam M.
Chellaganesh, Duraipandi
Winowlin Jappes, J. T.
Haider, Julfikar
Powiązania:
https://bibliotekanauki.pl/articles/2125539.pdf
Data publikacji:
2022
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
Wire Electro Spark Erosion
machining
NiTi alloy
surface roughness
material removal rate
MRR
Opis:
In this paper, a study was carried out to investigate the surface roughness and material removal rate of low carbon NiTi shape memory alloy (SMA) machined by Wire Electro Spark Erosion (WESE) technique. Experiments are designed considering three parameters viz, spark ON time (SON), spark OFF time (SOFF), and voltage (V) at three levels each. The surface roughness increased from 2.1686 μm to 2.6869 μm with an increase in both SON time, SOFF time and a decrease in voltage. The material removal rate increased from 1.272 mm3/min to 1.616 mm3/min with an increase in SON time but a varying effect was observed the SOFF time and voltage were varied. The analysis revealed that the intensity and duration of the spark had an unswerving relation with the concentration of the microcracks and micropores. More microcracks and micropores were seen in the combination of SON = 120 μs, voltage = 30 V. The concentration of the microcracks and micropores could be minimised by using an appropriate parameter setting. Therefore, considering the surface analysis and material removal, the low carbon NiTi alloy is recommended to machine with 110 μs - 55 μs - 30 V (SON - SOFF - V respectively), to achieve better surface roughness with minimal surface damage.
Źródło:
Archives of Metallurgy and Materials; 2022, 67, 3; 921--930
1733-3490
Pojawia się w:
Archives of Metallurgy and Materials
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Development of Electrically Conductive Nanocrystalline Thin Film for Optoelectronic Applications
Autorzy:
Das, S K.
Islam, J. M. M.
Hasan, M.
Kabir, H.
Gafur, Md. A.
Hoque, E.
Khan, M. A.
Powiązania:
https://bibliotekanauki.pl/articles/412543.pdf
Data publikacji:
2013
Wydawca:
Przedsiębiorstwo Wydawnictw Naukowych Darwin / Scientific Publishing House DARWIN
Tematy:
Conductive thin film
Composite
TiO2
Solar cell
Optoelectronics
Sodium alginate
Opis:
Sodium alginate (TiO2) sand composites were prepared by solution casting. Purified sand was added in the composite films to increase electrical conductivity. Electrical properties such as conductivity, capacitance, dielectric constant, and loss tangent of the composites were investigated. The current voltage characteristics for all the composites showed ohmic behavior. All the electrical properties have been found to improve with the incorporation of sand (SiO2) but 6 % sand containing composite exhibits the best electrical properties. The mechanical properties tensile strength (TS), elongation at break (Eb) and Young modulus for 6 % sand containing composite film are found to be 4.445 MPa, 9.76 %, and 72.8 MPa respectively. The experimental results reveal that the blended films exhibit higher stability and improved mechanical properties of both tensile strength and elongation at break in dry state. Water absorption properties of the composites are found to decrease with the increase of sand content. Lowest water uptake properties and highest stability were demonstrated by 6 % sand containing sample. Electrically conductive composite films have useful applications for solar cells and optoelectronics. Thus, this study is very much expected to aid in the design and selection of proper composite for the potential application of solar cell and optoelectronics.
Źródło:
International Letters of Chemistry, Physics and Astronomy; 2013, 10, 1; 90-101
2299-3843
Pojawia się w:
International Letters of Chemistry, Physics and Astronomy
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Fault Diagnosis of Three Phase Induction Motor Using Current Signal, MSAF-Ratio15 and Selected Classifiers
Autorzy:
Glowacz, A.
Glowacz, W.
Glowacz, Z.
Kozik, J.
Gutten, M.
Korenciak, D.
Khan, Z. F.
Irfan, M.
Carletti, E.
Powiązania:
https://bibliotekanauki.pl/articles/356557.pdf
Data publikacji:
2017
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
fault
current
electrical signals
induction motor
diagnostics
classification
Opis:
A degradation of metallurgical equipment is normal process depended on time. Some factors such as: operation process, friction, high temperature can accelerate the degradation process of metallurgical equipment. In this paper the authors analyzed three phase induction motors. These motors are common used in the metallurgy industry, for example in conveyor belt. The diagnostics of such motors is essential. An early detection of faults prevents financial loss and downtimes. The authors proposed a technique of fault diagnosis based on recognition of currents. The authors analyzed 4 states of three phase induction motor: healthy three phase induction motor, three phase induction motor with 1 faulty rotor bar, three phase induction motor with 2 faulty rotor bars, three phase induction motor with faulty ring of squirrel-cage. An analysis was carried out for original method of feature extraction called MSAF-RATIO15 (Method of Selection of Amplitudes of Frequencies – Ratio 15% of maximum of amplitude). A classification of feature vectors was performed by Bayes classifier, Linear Discriminant Analysis (LDA) and Nearest Neighbour classifier. The proposed technique of fault diagnosis can be used for protection of three phase induction motors and other rotating electrical machines. In the near future the authors will analyze other motors and faults. There is also idea to use thermal, acoustic, electrical, vibration signal together.
Źródło:
Archives of Metallurgy and Materials; 2017, 62, 4; 2413-2419
1733-3490
Pojawia się w:
Archives of Metallurgy and Materials
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Gamma radiation treated chitosan solution for strawberry preservation: Physico-chemical properties and sensory evaluation
Autorzy:
Jesmin, S.
Al-Jubayer, A.
bin Eusuf, S.
Kamal, A.H.M.
Islam, J.M.M.
Ferdoush, F.
Kabir, S.E.
Khan, M.A.
Powiązania:
https://bibliotekanauki.pl/articles/11054.pdf
Data publikacji:
2016
Wydawca:
Przedsiębiorstwo Wydawnictw Naukowych Darwin / Scientific Publishing House DARWIN
Źródło:
International Letters of Natural Sciences; 2016, 60
2300-9675
Pojawia się w:
International Letters of Natural Sciences
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Phytochemical screening of Pulsatilla species and investigation of their biological activities
Autorzy:
Laska, G.
Sienkiewicz, A.
Stocki, M.
Zjawiony, J.K.
Sharma, V.
Bajguz, A.
Piotrowska-Niczyporuk, A.
Jacob, M.
Khan, S.
Powiązania:
https://bibliotekanauki.pl/articles/56981.pdf
Data publikacji:
2019
Wydawca:
Polskie Towarzystwo Botaniczne
Opis:
The present study aimed to identify biologically active secondary metabolites from the rare plant species, Pulsatilla patens subsp. patens and the cultivated P. vulgaris subsp. vulgaris. Chromatographic fractionation of the ethanolic extract of the roots of P. patens subsp. patens resulted in the isolation of two oleanane-type glycosides identified as hederagenin 3-O-β-d-glucopyranoside (2.7 mg) and hederagenin 3-O-β-d-galactopyranosyl-(1→2)-β-d-glucopyranoside (3.3 mg, patensin). HPLC analysis of the methanolic extract of the crude root of P. patens subsp. patens and P. vulgaris subsp. vulgaris revealed the presence of Pulsatilla saponin D (hederagenin 3-O-α-l-rhamnopyranosyl(1→2)-[β-d-glucopyranosyl(1→4)]-α-l-arabinopyranoside). Chromatographic analysis using GC-MS of the silylated methanolic extracts from the leaves and roots of these species identified the presence of carboxylic acids, such as benzoic, caffeic, malic, and succinic acids. The extracts from Pulsatilla species were tested for their antifungal, antimicrobial, and antimalarial activities, and cytotoxicity to mammalian cell lines. Both P. patens subsp. patens and P. vulgaris subsp. vulgaris were active against the fungus Candida glabrata with the half-maximal inhibitory concentration (IC₅₀) values of 9.37 μg/mL and 11 μg/mL, respectively. The IC₅₀ values for cytotoxicity evaluation were in the range of 32–38 μg/mL for P. patens subsp. patens and 35–57 μg/mL for P. vulgaris subsp. vulgaris for each cell line, indicating general cytotoxic activity throughout the panel of evaluated cancer and noncancer cells.
Źródło:
Acta Societatis Botanicorum Poloniae; 2019, 88, 1
0001-6977
2083-9480
Pojawia się w:
Acta Societatis Botanicorum Poloniae
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Incidence and molecular characterization of extended-spectrum beta-lactamase (ESBL)-producing Salmonella enterica and Escherichia coli of avifauna origin in Pakistan
Autorzy:
Saeed, M.A.
Waheed, U.
Ehtisham-ul-Haque, S.
Khan, A.U.
Kashif, M.
Qamar, M.F.
Ghafoor, A.
Saqlain, M.
Asghar, J.
Powiązania:
https://bibliotekanauki.pl/articles/16647457.pdf
Data publikacji:
2023
Wydawca:
Polska Akademia Nauk. Czasopisma i Monografie PAN
Tematy:
ESBL
genotypic characterization
Salmonella enterica
Escherichia coli
avifauna
Pakistan
Opis:
Members of Enterobacteriaceae are known to produce extended-spectrum beta-lactamases (ESBL) which hydrolyze the beta-lactam group of antibiotics. The existence of ESBL-producing Salmonella enterica (S. enterica) and Escherichia coli (E. coli) harbored by urban avifauna was investigated in this study. Dropping samples (n= 180) were collected from six different bird species in the district Jhang, Punjab province, Pakistan. Isolation and identification of ESBL isolates were made by using cefotaxime- (4 mg/L) supplemented MacConkey agar and double disc synergy test (DDST). Polymerase chain reaction (PCR) was performed for the detection of four different ESBL genes including bla CTX-M, bla TEM, bla SHV and bla OXA. A total of 42.69% isolates were confirmed as ESBL via DDST including 30.64% S. enterica and 49.54% E. coli. The incidence of ESBL S. enterica and ESBL E. coli was found highest in egret (Ardea alba) and pigeon (Columba livia) as 64.28% and 78.95%, respectively. The bla CTX-M gene was detected in 57.89% and 64.81% of isolates of S. enterica and E. coli, respectively. Among other genes in S. enterica and E. coli, bla TEM (21.05%, 20.4%); bla SHV (15.78%, 9.26%), and bla OXA (5.26%, 5.56%) were detected, respectively. All of the tested isolates were found resistant to at least one of the thirteen antimicrobial agents except meropenem. To the best of our knowledge, this is the first study reporting the incidence and genetic diversity of ESBL bacteria associated with urban avifauna in Pakistan. The urban avifauna can serve as a potential subject of bio-surveillance to monitor the emergence of antimicrobial-resistant bacteria.
Źródło:
Polish Journal of Veterinary Sciences; 2023, 26, 1; 47-55
1505-1773
Pojawia się w:
Polish Journal of Veterinary Sciences
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Radiotracer investigations of municipal sewage treatment stations
Autorzy:
Farooq, M.
Khan, I.
Ghiyas-ud-Din, Ghiyas-ud-Din
Gul, S.
Palige, J.
Dobrowolski, A.
Powiązania:
https://bibliotekanauki.pl/articles/971492.pdf
Data publikacji:
2003
Wydawca:
Instytut Chemii i Techniki Jądrowej
Tematy:
wastewater treatment
residence time distribution
activated sludge
radiotracer
Opis:
Tracer techniques, which are well-established methods in process dynamics studies in industry, were applied to investigate the dynamics of sewage treatment process. The concept of residence time distribution (RTD) was used to investigate the efficiency of the primary clarifier, aeration tank and secondary clarifier of a sewage treatment plant. Preliminary treatment and modeling of the tracer data was performed using the software DTS Pro Ver. 4.20. A big short - circuiting (by-passing) with a large volume of stagnant zones were found in the primary and secondary clarifiers, while no stagnant zone was detected in the aeration tank.
Źródło:
Nukleonika; 2003, 48, 1; 57-61
0029-5922
1508-5791
Pojawia się w:
Nukleonika
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Luminescence of Highly Excited Nonpolar a-Plane GaN and AlGaN/GaN Multiple Quantum Wells
Autorzy:
Juršėnas, S.
Kuokštis, E.
Miasojedovas, S.
Kurilčik, G.
Žukauskas, A.
Chen, C. Q.
Yang, J. W.
Adivarahan, V.
Asif Khan, M.
Powiązania:
https://bibliotekanauki.pl/articles/2038100.pdf
Data publikacji:
2004-06
Wydawca:
Polska Akademia Nauk. Instytut Fizyki PAN
Tematy:
78.55.Cr
73.21.Fg
72.20.Jv
78.47.+p
Opis:
Carrier recombination dynamics in polar and nonpolar GaN epilayers and GaN/AlGaN multiple quantum wells grown over sapphire substrates with various crystallographic orientation were studied under high photoexcitation by 20 ps laser pulses. The transient of luminescence featured a significant enhancement in nonradiative recombination of free carriers for nonpolar a-plane GaN epilayers compared to conventional c-plane samples. The epitaxial lateral overgrowth technique was demonstrated to significantly improve the quality of nonpolar a-plane films. This was proved by more than 40-fold increase in luminescence decay time (430 ps compared to ≤10 ps in the ordinary a-plane epilayer). Under high-excitation regime, a complete screening of built-in electric field by free carriers in multiple quantum wells grown on c-plane and r-plane sapphire substrates was achieved. Under such high excitation, luminescence efficiency and carrier lifetime of multiple quantum wells was shown to be determined by the substrate quality.
Źródło:
Acta Physica Polonica A; 2004, 105, 6; 567-573
0587-4246
1898-794X
Pojawia się w:
Acta Physica Polonica A
Dostawca treści:
Biblioteka Nauki
Artykuł
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