101
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Ahmad H, Zulkifli MZ, Hassan NA, Harun SW. S-band multiwavelength ring Brillouin/Raman fiber laser with 20 GHz channel spacing. APPLIED OPTICS 2012; 51:1811-1815. [PMID: 22505174 DOI: 10.1364/ao.51.001811] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2011] [Accepted: 01/28/2012] [Indexed: 05/31/2023]
Abstract
We propose and demonstrate a tunable S-band multiwavelength Brillouin/Raman fiber laser (MBRFL) with a tuning range of between 1490 to 1530 nm. The proposed MBRFL is designed around a 7.7 km long dispersion compensating fiber in a simple ring configuration, acting as a nonlinear medium for the generation of multiple wavelengths from stimulated Brillouin scattering (SBS) and also as a nonlinear gain medium for stimulated Raman scattering (SRS) amplification. A laser source with a maximum power of 12 dBm acts as the Brillouin pump (BP), while two 1420 nm laser diodes with a total power of 26 dBm act as the Raman pumps (RPs). The MBRFL can generate a multiwavelength comb consisting of even and odd Stokes at an average power of -12 dBm and -14 dBm respectively, and by separating the even and odd Stokes outputs, a 20 GHz channel spacing is obtained between two consecutive wavelengths. Due to the four-wave mixing (FWM) effect, anti-Stokes lines are also observed. The multiwavelength comb generated is not dependent on the BP, thus providing high stability and repeatability and making it a highly potential source for many real-world applications. This is the first time, to the knowledge of the authors, that a tunable MBRFL has been developed using SRS to obtain gain in the S-band region.
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102
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Moghaddam MRA, Harun SW, Ahmad H. Comparison between Analytical Solution and Experimental Setup of a Short Long Ytterbium Doped Fiber Laser. ACTA ACUST UNITED AC 2012. [DOI: 10.4236/opj.2012.22010] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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103
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Chong WY, Lim KS, Lim WH, Harun SW, Adikan FRM, Ahmad H. Spreading profile of evaporative liquid drops in thin porous layer. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2012; 85:016314. [PMID: 22400665 DOI: 10.1103/physreve.85.016314] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2011] [Revised: 10/13/2011] [Indexed: 05/31/2023]
Abstract
Spreading of evaporative liquid drops in a thin porous layer has been studied. The entire spreading process can be divided into three distinct phases according to the change of the wetted porous region size. The first phase is characterized by the expansion of the wetted porous region and shrinking of the liquid drop. Contact line pinning is observed in the wetted porous region in the second phase even with the liquid drop totally absorbed into the porous layer. The third phase sees the shrinkage of the wetted porous region until it is not observable. Based on these observations, a model is devised to simulate the spreading of a liquid drop under the studied conditions. Partial differential equations are used to describe the relation between liquid drop volume and other important parameters of a fluid flow, including maximum wetted region diameter achieved, time taken to reach each spreading process phase, and evaporation rate. Calculated results are in good agreement with the experimental data.
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104
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Cheong YK, Lim KS, Lim WH, Chong WY, Zakaria R, Ahmad H. Note: Fabrication of tapered fibre tip using mechanical polishing method. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2011; 82:086115. [PMID: 21895293 DOI: 10.1063/1.3627374] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
Tapered fibre tips fabricated using mechanical polishing method is studied. The fibre tips are formed by sequential polishing flat-ended single mode fibres with decreasing aluminium oxide polishing film grit size. Based on the proposed technique, tapered fibre tips with cone angle ranging from 30° to 130° are fabricated by controlling the polishing angle. Besides the variety of cone angle, considerable smoothness of the fibre tip surface may assist in good metal coating and hence a well-defined aperture can be obtained. In addition, this paper presents a two-step hybrid fabrication method combining the proposed polishing method with chemical etching method to increase the possible fibre tip cone angles achievable by chemical etching method.
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105
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Rahman MA, Alam MS, Miah MAJ, Rahman MM, Dupin D, Ahmad H. Nanosized nickel oxide particles and modification with poly(methyl methacrylate). POLYM ADVAN TECHNOL 2011. [DOI: 10.1002/pat.2026] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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106
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Harun SW, Dimyati K, Tamjis MR, Muhd-Yassin SZ, Abd-Rahman MK, Ahmad H. Efficient and Compact Optical Amplifier Using EYDF. IIUM ENGINEERING JOURNAL 2010; 8:17-23. [DOI: 10.31436/iiumej.v8i2.89] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/02/2023]
Abstract
An efficient Erbium/Ytterbium doped fiber amplifier (EYDFA) is demonstrated using a 1058nm pumping wavelength, where the amplification is assisted by energy transfer between Yb and Er ions. The energy transfer increases the limit of erbium doping concentration that is imposed by concentration quenching in Erbium-doped fiber (EDF). Therefore, the gain and noise figure are severely degraded with 1480 nm pumping, where the energy transfer cannot be achieved. The use of optical isolator improves the small signal gain and noise figure by about 4.8 dB and 1.6 dB, respectively. By employing a double-pass configuration, a higher gain can be obtained with an expense of a noise figure penalty. The gain improvement of 17.0 dB is obtained at 20 mW and -50 dBm of pump and input signal powers. This shows that the double-pass configuration is an important aspect to consider when designing an efficient EYDFA.
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107
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Paul MC, Harun SW, Huri NAD, Hamzah A, Das S, Pal M, Bhadra SK, Ahmad H, Yoo S, Kalita MP, Boyland AJ, Sahu JK. Performance comparison of Zr-based and Bi-based erbium-doped fiber amplifiers. OPTICS LETTERS 2010; 35:2882-2884. [PMID: 20808356 DOI: 10.1364/ol.35.002882] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
In this Letter, we present a comprehensive comparison of the performance of a zirconia-based erbium-doped fiber amplifier (Zr-EDFA) and a bismuth-based erbium-doped fiber amplifier (Bi-EDFA). The experimental results reveal that a Zr-EDFA can achieve comparable performance to the conventional Bi-EDFA for C-band and L-band operations. With a combination of both Zr and Al, we could achieve a high erbium-doping concentration of about 2800 ppm (parts per million) in the glass host without any phase separations of rare earths. The Zr-based erbium-doped fiber (Zr-EDF) was fabricated using in a ternary glass host, zirconia-yttria-aluminum codoped silica fiber through a solution-doping technique along with modified chemical vapor deposition. At a high input signal of 0 dBm, a flat gain at average value of 13 dB is obtained with a gain variation of less than 2 dB within the wavelength region of 1530-1575 nm and using 2 m of Zr-EDF and 120 mW pump power. The noise figures are less than 9.2 at this wavelength region. It was found that a Zr-EDFA can achieve even better flat-gain value and bandwidth as well as lower noise figure than the conventional Bi-EDFA.
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108
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Emami S, Harun S, Abd-Rahman F, Abdul-Rashid H, Daud S, Ghani Z, Ahmad H. A theoretical study of double-pass thulium-doped fiber amplifiers. OPTIK 2010; 121:1257-1262. [DOI: 10.1016/j.ijleo.2009.01.017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/02/2023]
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109
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Wolfe J, Reijnen E, Ahmad H, VanWert M. Where would you look? Guiding visual search with global spatial information. J Vis 2010. [DOI: 10.1167/7.9.719] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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110
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Tan TL, Ahmad H, Jhavar R, Patel R, Harrison C, Oteng-Ntim E. Use of erythropoietin in a pregnant Jehovah's Witness with sickle-cell disease. J OBSTET GYNAECOL 2009; 27:82-3. [PMID: 17365469 DOI: 10.1080/01443610601062739] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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111
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Tahir M, Das CJ, Ahmad FU, Ahmad H. Dorsal intramedullary tuberculoma. CASE REPORTS 2009; 2009:bcr2007116012. [DOI: 10.1136/bcr.2007.116012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
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112
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Ahmad H, Shahi S, Harun SW. Multi-wavelength laser generation with Bismuthbased Erbium-doped fiber. OPTICS EXPRESS 2009; 17:203-207. [PMID: 19129889 DOI: 10.1364/oe.17.000203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
A multi-wavelength laser comb is demonstrated using a nonlinear effect in a backward pumped Bismuth-based Erbium-doped fiber (Bi-EDF) for the first time. It uses a ring cavity resonator scheme containing a 215 cm long highly nonlinear Bi-EDF, optical isolators, polarisation controller and 10 dB output coupler. The laser generates more than 10 lines of optical comb with a line spacing of approximately 0.41 nm at 1615.5 nm region using 146 mW of 1480 nm pump power.
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113
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Harun SW, Shahi S, Ahmad H. Compact Brillouin-erbium fiber laser. OPTICS LETTERS 2009; 34:46-48. [PMID: 19109635 DOI: 10.1364/ol.34.000046] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
A single-wavelength Brillouin fiber laser (BFL) is demonstrated at the extended L-band region using bismuth-based erbium-doped fiber (Bi-EDF) for the first time to the best of our knowledge. A 2.15-m-long Bi-EDF is used to provide both nonlinear and linear gains to generate a stimulated Brillouin scattering (SBS) and to amplify the generated SBS, respectively. The BFL operates at 1613.93 nm, which is upshifted by 0.09 nm from the Brillouin pump with a peak power of 2 dBm and a side-mode suppression ratio of more than 22 dB. The generated BFL has a narrow linewidth and many potential applications, such as in optical communication and sensors.
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Sood R, Kathuria S, Ahmad H, Ahir M. UP.34: A Comparative Head-On Efficacy Study of 3 Monthly Goserelin 10.8 Mg, 3 Monthly Leuprolide 11.25 Mg and 3 Monthly Leuprolide 22.5 Mg with 6 Monthly Leuprolide 45mg Preparations for Treatment in Patients with Prostate Cancer. Urology 2008. [DOI: 10.1016/j.urology.2008.08.357] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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115
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Emami SD, Harun SW, Abd-Rahman F, Abdul-Rashid HA, Ahmad H. Effects of an auxiliary pump on the performance of TDFA. LASER PHYSICS 2008; 18:977-982. [DOI: 10.1134/s1054660x08080112] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/02/2023]
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116
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Shirazi MR, Biglary M, Harun SW, Thambiratnam K, Ahmad H. Effects of different Raman pumping schemes on stimulated Brillouin scattering in a linear cavity. APPLIED OPTICS 2008; 47:3088-3091. [PMID: 18545279 DOI: 10.1364/ao.47.003088] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The effects of backward, forward, and bidirectional Raman pumping schemes on stimulated Brillouin scattering (SBS) is investigated in this study. By using a linear cavity, we utilize residual Brillouin pump (BP) and Raman pump (RP) power after each transmission through a 25 km single-mode fiber (SMF) used as a gain medium. The SBS threshold power is reduced in the forward, backward, and bidirectional Raman pumping schemes by 2.5, 1.75, and 2.75 dB, respectively when the 1480 nm RP power is fixed at 150 mW and the BP wavelength is 1580 nm. Surprisingly, it is revealed that the SBS threshold reduction depends strongly and solely on Raman gain and it is independent of the Raman pumping schemes. In addition, the effect of Raman amplification on SBS is more effective at the SBS threshold, especially in the bidirectional and forward schemes.
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117
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Shirazi MR, Harun SW, Biglary M, Ahmad H. Linear cavity Brillouin fiber laser with improved characteristics. OPTICS LETTERS 2008; 33:770-772. [PMID: 18414527 DOI: 10.1364/ol.33.000770] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
A configuration for linear cavity Brillouin fiber laser (BFL) generation is demonstrated using a standard single-mode fiber, two optical circulators, a 3 dB coupler, and a 95/5 coupler to allow high efficiency. With a Brillouin pump (BP) power of 13 dBm, the laser peak power is 12.3 dB higher than a conventional linear cavity BFL at an upshifted wavelength of 0.086 nm from the BP wavelength. In addition, it is revealed that the BFL peak power can be higher than the transmitted BP peak power when the BP power exceeds the second Brillouin Stokes threshold power.
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118
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Ghafoor S, Shah MM, Ahmad H, Swati ZA, Shah SH, Pervez A, Farooq U. Molecular characterization of Ephedra species found in Pakistan. GENETICS AND MOLECULAR RESEARCH 2007; 6:1123-1130. [PMID: 18273806] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Ephedra, also known as "ma huang", is a dioecious, drought- and frost-resistant, perennial, evergreen shrub with compelling medicinal value. The genus is represented by 42 species around the world, 9 of which were provisionally reported from Pakistan. Species of the genus have a controversial taxonomy due to their overlapping morphological features. Conventional tools alone are not sufficient for characterizing the species. The objective of present study was to assess the genetic variability present in different biotypes of Ephedra growing in Pakistan using molecular markers. A total of six genotypes collected from diverse geographic zones of Pakistan were used. The DNA of all genotypes was amplified using nine randomly amplified polymorphic DNA (RAPD) primers to study genetic variability at the molecular level. The dissimilarity coefficient matrix based on the data of 9 RAPD primers was used to construct a dendrogram which was then used to group the genotypes in clusters. Based on the dendrogram and dissimilarity coefficient matrix, the RAPD markers used here revealed a moderate to high level of genetic polymorphism (6 to 49%) among the genotypes. It was found that the collection of genotype accessions from Swat Valley in northwestern Pakistan was most distantly related to the other five collections. More molecular markers including functional genes and ribosomal spacer regions are suggested to find a better estimate of the genetic diversity present in Ephedra growing in Pakistan. The information provided here is useful for identifying valuable Ephedra variants which will be used for medicinal purposes and earning foreign currency.
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119
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Muhd-Yassin SZ, Harun SW, Abdul-Rashid HA, Abd-Rahman MK, Rahman FA, Ahmad H. An efficient EYDFA with a 54 dB small signal gain. MICROWAVE AND OPTICAL TECHNOLOGY LETTERS 2007; 49:2337-2339. [DOI: 10.1002/mop.22750] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/01/2023]
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120
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Harun SW, Emami SD, Abd Rahman F, Muhd-Yassin SZ, Abd-Rahman MK, Ahmad H. Multiwavelength Brillouin/Erbium-Ytterbium fiber laser. LASER PHYSICS LETTERS 2007; 4:601-603. [DOI: 10.1002/lapl.200710035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/01/2023]
Abstract
A multi-wavelength Brillouin/Erbium-Ytterbium doped fiber laser which operates in the 1535 nm region is proposed and demonstrated. The system employs both linear and nonlinear gain from a 4 meter Erbium-Ytterbium doped fiber and an 8 km single mode fiber respectively to generate an optical comb with a spacing of approximately 0.084 nm. A stable output laser comb of more than 22 lines was obtained with a Brillouin pump of 2 dBm and a 1058 nm pump of 175 mW. A maximum peak power of -4.2 dBm was obtained at a wavelength of 1535.16 nm at these pump power settings while the spectral linewidth of the laser is approximately 8 Hz.
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121
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Muhd-Yassin SZ, Harun SW, Ahmad H, Abd-Rahman MK. Highly saturated EDFA for gain clamping operation. MICROWAVE AND OPTICAL TECHNOLOGY LETTERS 2007; 49:1815-1816. [DOI: 10.1002/mop.22635] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/02/2023]
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122
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Harun SW, Abd Rahman F, Dimyati K, Ahmad H. An efficient gain-flattened C-band Erbium-doped fiber amplifier. LASER PHYSICS LETTERS 2006; 3:536-538. [DOI: 10.1002/lapl.200610048] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/02/2023]
Abstract
An efficient gain-flattened C-band Erbium-doped fibre
amplifier is demonstrated using a double-pass configuration with
an IsoGainTM Erbium-doped fibre (EDF). The amplifier
utilizes a double-propagation of signal provided by an optical
circulator at the output end of the EDF to obtain an improved
flat-gain characteristic. At input signal power of -10 dBm, a
flat-gain of 25 dB was obtained from wavelength region from 1528
to 1568 nm. This amplifier has the potential to be used in the
high channel count dense wavelength division multiplexing system
because of its simplicity and low cost.
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123
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Blot C, Desouza D, Ahmad H, Shelden R, Kemmann E. P-291. Fertil Steril 2006. [DOI: 10.1016/j.fertnstert.2006.07.645] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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124
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Harun SW, Abdul-Rashid HA, Muhd-Yassin SZ, Abd-Rahman MK, Tamjis MR, Ahmad H. Dual-stage Er/Yb doped fiber amplifier for gain and noise figure enhancements. IEICE ELECTRONICS EXPRESS 2006; 3:517-521. [DOI: 10.1587/elex.3.517] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/02/2023]
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125
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Brandes J, Grossman SA, Ahmad H. Management of pemetrexed toxicity in acute renal failure. J Clin Oncol 2005. [DOI: 10.1200/jco.2005.23.16_suppl.2121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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