Displaying publications 1 - 20 of 85 in total

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  1. COVID-19 vaccination in South Asia: a call for responsible leadership among SAARC countries
    Haque A, Islam MS
    Leadersh Health Serv (Bradf Engl), 2021 Dec 03;ahead-of-print(ahead-of-print).
    PMID: 34854657 DOI: 10.1108/LHS-09-2021-0077
    PURPOSE: Coronavirus, also known as COVID-19, has presented an opportunity to set aside traditional regional collaborations and take responsible leadership to overcome difficult times. This paper aims to explore the current COVID-19 vaccination progress and pandemic status for the South Asian Association for Regional Cooperation (SAARC) countries and suggests responsible leadership to combat the COVID-19 pandemic and to think beyond.

    DESIGN/METHODOLOGY/APPROACH: This paper offers a viewpoint of the current COVID-19 vaccination among eight SAARC nations. It scrutinises the recent COVID-19 vaccination statistics for the eight South Asian countries based on Web-based analytics and comparative analysis until 28 August 2021.

    FINDINGS: This paper calls for collaborative decisions and responsible actions for policymakers in the SAARC countries to deal with the COVID-19 vaccination crisis. When South Asian countries are fraught with the increasing number of populations with COVID-19 cases, deaths and acute shortage of life-saving vaccines, it is time for their national and SAARC leaders to strengthen regional cooperations and initiate collaborative actions. The paper demonstrates that implementing responsible leadership can result in favourable outcomes for individuals, organisations, regions and the world. Moreover, this paper suggests SAARC, through responsible actions, has the potentiality to overcome the current crisis of COVID-19 vaccination and enhance the regional sustainability of the South Asian nations.

    ORIGINALITY/VALUE: This paper delivers information about the present developing situation of COVID-19 vaccination in SAARC countries, how the governments and regional leadership are handling and future challenges that have been raised and can be overcome effectively. This paper can be helpful for the policymakers and SAARC leaders for effective public health interventions in the region and to develop a recovery roadmap for the sustainable economic zone.

  2. Fulltext Alpinia calcarata Roscoe: A potential phytopharmacological source of natural medicine
    Rahman MA, Islam MS
    Pharmacogn Rev, 2015 Jan-Jun;9(17):55-62.
    PMID: 26009694 DOI: 10.4103/0973-7847.156350
    Alpinia calcarata Roscoe (Family: Zingiberaceae), is a rhizomatous perennial herb, which is commonly used in the traditional medicinal systems in Sri Lanka. Alpinia calcarata is cultivated in tropical countries, including Sri Lanka, India, and Malaysia. Experimentally, rhizomes of Alpinia calcarata are shown to possess antibacterial, antifungal, anthelmintic, antinociceptive, anti-inflammatory, antioxidant, aphrodisiac, gastroprotective, and antidiabetic activities. Phytochemical screening revealed the presence of polyphenols, tannins, flavonoids, steroid glycosides and alkaloids in the extract and essential oil of this plant. Essential oil and extracts from this plant have been found to possess wide range of pharmacological and biological activities. This article provides a comprehensive review of its ethnomedical uses, chemical constituents and the pharmacological profile as a medicinal plant. Particular attention has been given to the pharmacological effects of the essential oil of Alpinia calcarata in this review so that the potential use of this plant either in pharmaceutics or as an agricultural resource can be evaluated.
  3. Fulltext Hardware implementation of 32-bit high-speed direct digital frequency synthesizer
    Ibrahim SH, Ali SH, Islam MS
    ScientificWorldJournal, 2014;2014:131568.
    PMID: 24991635 DOI: 10.1155/2014/131568
    The design and implementation of a high-speed direct digital frequency synthesizer are presented. A modified Brent-Kung parallel adder is combined with pipelining technique to improve the speed of the system. A gated clock technique is proposed to reduce the number of registers in the phase accumulator design. The quarter wave symmetry technique is used to store only one quarter of the sine wave. The ROM lookup table (LUT) is partitioned into three 4-bit sub-ROMs based on angular decomposition technique and trigonometric identity. Exploiting the advantages of sine-cosine symmetrical attributes together with XOR logic gates, one sub-ROM block can be removed from the design. These techniques, compressed the ROM into 368 bits. The ROM compressed ratio is 534.2:1, with only two adders, two multipliers, and XOR-gates with high frequency resolution of 0.029 Hz. These techniques make the direct digital frequency synthesizer an attractive candidate for wireless communication applications.
  4. Fulltext Experimental tissue mimicking human head phantom for estimation of stroke using IC-CF-DMAS algorithm in microwave based imaging system
    Islam MS, Islam MT, Almutairi AF
    Sci Rep, 2021 11 10;11(1):22015.
    PMID: 34759284 DOI: 10.1038/s41598-021-01486-x
    This paper presents the preparation and measurement of tissue-mimicking head phantom and its validation with the iteratively corrected coherence factor delay-multiply-and-sum (IC-CF-DMAS) algorithm for brain stroke detection. The phantom elements are fabricated by using different chemical mixtures that imitate the electrical properties of real head tissues (CSF, dura, gray matter, white matter, and blood/stroke) over the frequency band of 1-4 GHz. The electrical properties are measured using the open-ended dielectric coaxial probe connected to a vector network analyzer. Individual phantom elements are placed step by step in a three-dimensional skull. The IC-CF-DMAS image reconstruction algorithm is later applied to the phantom to evaluate the effectiveness of detecting stroke. The phantom elements are preserved and measured multiple times in a week to validate the overall performance over time. The electrical properties of the developed phantom emulate the similar properties of real head tissue. Moreover, the system can also effectively detect the stroke from the developed phantom. The experimental results demonstrate that the developed tissue-mimicking head phantom is time-stable, and it shows a good agreement with the theoretical results in detecting and reconstructing the stroke images that could be used in investigating as a supplement to the real head tissue.
  5. Solid waste bin detection and classification using Dynamic Time Warping and MLP classifier
    Islam MS, Hannan MA, Basri H, Hussain A, Arebey M
    Waste Manag, 2014 Feb;34(2):281-90.
    PMID: 24238802 DOI: 10.1016/j.wasman.2013.10.030
    The increasing requirement for Solid Waste Management (SWM) has become a significant challenge for municipal authorities. A number of integrated systems and methods have introduced to overcome this challenge. Many researchers have aimed to develop an ideal SWM system, including approaches involving software-based routing, Geographic Information Systems (GIS), Radio-frequency Identification (RFID), or sensor intelligent bins. Image processing solutions for the Solid Waste (SW) collection have also been developed; however, during capturing the bin image, it is challenging to position the camera for getting a bin area centralized image. As yet, there is no ideal system which can correctly estimate the amount of SW. This paper briefly discusses an efficient image processing solution to overcome these problems. Dynamic Time Warping (DTW) was used for detecting and cropping the bin area and Gabor wavelet (GW) was introduced for feature extraction of the waste bin image. Image features were used to train the classifier. A Multi-Layer Perceptron (MLP) classifier was used to classify the waste bin level and estimate the amount of waste inside the bin. The area under the Receiver Operating Characteristic (ROC) curves was used to statistically evaluate classifier performance. The results of this developed system are comparable to previous image processing based system. The system demonstration using DTW with GW for feature extraction and an MLP classifier led to promising results with respect to the accuracy of waste level estimation (98.50%). The application can be used to optimize the routing of waste collection based on the estimated bin level.
  6. Fulltext Investigation into mass loading sensitivity of sezawa wave mode-based surface acoustic wave sensors
    Mohanan AA, Islam MS, Ali SH, Parthiban R, Ramakrishnan N
    Sensors (Basel), 2013;13(2):2164-75.
    PMID: 23389346 DOI: 10.3390/s130202164
    In this work mass loading sensitivity of a Sezawa wave mode based surface acoustic wave (SAW) device is investigated through finite element method (FEM) simulation and the prospects of these devices to function as highly sensitive SAW sensors is reported. A ZnO/Si layered SAW resonator is considered for the simulation study. Initially the occurrence of Sezawa wave mode and displacement amplitude of the Rayleigh and Sezawa wave mode is studied for lower ZnO film thickness. Further, a thin film made of an arbitrary material is coated over the ZnO surface and the resonance frequency shift caused by mass loading of the film is estimated. It was observed that Sezawa wave mode shows significant sensitivity to change in mass loading and has higher sensitivity (eight times higher) than Rayleigh wave mode for the same device configuration. Further, the mass loading sensitivity was observed to be greater for a low ZnO film thickness to wavelength ratio. Accordingly, highly sensitive SAW sensors can be developed by coating a sensing medium over a layered SAW device and operating at Sezawa mode resonance frequency. The sensitivity can be increased by tuning the ZnO film thickness to wavelength ratio.
  7. Prevalence of Hepatitis B Virus, Hepatitis C Virus, and HIV in Overseas Job Seekers of Bangladesh with the Possible Routes of Transmission
    Jobayer M, Chowdhury SS, Shamsuzzaman SM, Islam MS
    Mymensingh Med J, 2016 07;25(3):530-5.
    PMID: 27612902
    Hepatitis and AIDS are major public health problem globally. The aim of this study was to determine the sero-prevalence of hepatitis B, C virus and HIV infection among Bangladeshi overseas job seekers. This cross sectional study was carried out in the Department of Microbiology of Dhaka Medical College, Dhaka, Bangladesh from February 2013 to August 2013. A total of 2254 adult (18-45 years) male job seekers to Malaysia attending for health check up were enrolled. HBsAg, Anti-HCV, Anti-HIV were detected from venous blood by ELISA method using commercial kits. From the positive people, further history and information were collected by predesigned questionnaire. Prevalence of HBV was 2.35%, HCV was 0.13% and none was found positive for HIV. Prevalence of hepatitis was higher in the age group of 21-30 year and infection was more prevalent in married group. No significant relationship was found between hepatitis infection and religion, localities, profession. Only a few cases had history of possible major known route of transmission of virus. But most of them had history of taking injection or sharing blades in barber shop and history of circumcision. About 96% population had no history of hepatitis B vaccination. None was co-infected with HBV and HCV. Prevalence of hepatitis B virus infection in adult population appears to be on decline and hepatitis C and HIV infection is still low in Bangladesh. In majority of the positive person, routes of transmission of viruses were not well established.
  8. Assessment of toxic metals in water and sediment of Pasur River in Bangladesh
    Ali MM, Ali ML, Islam MS, Rahman MZ
    Water Sci Technol, 2018 Mar;77(5-6):1418-1430.
    PMID: 29528329 DOI: 10.2166/wst.2018.016
    This study was conducted to assess the levels of toxic metals like arsenic (As), chromium (Cr), cadmium (Cd), and lead (Pb) in water and sediments of the Pasur River in Bangladesh. The ranges of Cr, As, Cd, Pb in water were 25.76-77.39, 2.76-16.73, 0.42-2.98 and 12.69-42.67 μg/L and in sediments were 20.67-83.70, 3.15-19.97, 0.39-3.17 and 7.34-55.32 mg/kg. The level of studied metals in water samples exceeded the safe limits of drinking water, indicating that water from this river is not safe for drinking and cooking. Certain indices, including pollution load index (PLI) and contamination factor (Cif) were used to assess the ecological risk. The PLI indicated progressive deterioration of sediments by the studied metals. Potential ecological risks of metals in sediment indicated low to considerable risk. However, the Cif values of Cd ranged from 0.86 to 8.37 revealed that the examined sediments were strongly impacted by Cd. Considering the severity of potential ecological risk (PER) for single metal (Eir), the descending order of contaminants was Cd > Pb > As > Cr. According the results, some treatment scheme must formulate and implement by the researchers and related management organizations to save the Pasur River from metals contamination.
  9. Fulltext Electric-Field-Coupled Resonator Antenna for 5G Applications
    Rahman MM, Islam MS, Islam MT, Alam T
    Materials (Basel), 2022 Jul 29;15(15).
    PMID: 35955182 DOI: 10.3390/ma15155247
    In this paper, a compact wideband patch antenna comprising a modified electric-field-coupled resonator with parasitic elements is presented. The resonance at low frequency is achieved due to the electric field polarization along the split of the conventional LC (inductive-capacitive) structure. However, this antenna gives low bandwidth as well as low gain. Some evolutionary techniques are adopted to get a compact wideband antenna at 3GPP bands of 5G. The split width and the ground plane are modified to achieve enhanced bandwidth with good impedance matching, whereas the addition of the parasitic elements on both sides of the microstrip feed line enhances the gain with a slight reduction of bandwidth. The compact dimension of the proposed antenna is 0.26 λL × 0.26 λL × 0.017 λL, where λL is the free space wavelength at the lowest frequency. A prototype of the presented design is fabricated and measured. Measurement shows that the antenna has an operating bandwidth of 19.74% for |S11| < −10 dB where the gain of 1.15 dBi is realized. In addition, the radiation pattern is omnidirectional in the horizontal plane and dumbbell shaped in the elevation plane. The cross-polarization levels in both planes are less than −12 dB.
  10. Fulltext Recent Advances in Shape-Controlled Synthesis of Noble Metal Nanoparticles by Radiolysis Route
    Abedini A, Bakar AA, Larki F, Menon PS, Islam MS, Shaari S
    Nanoscale Res Lett, 2016 Dec;11(1):287.
    PMID: 27283051 DOI: 10.1186/s11671-016-1500-z
    This paper focuses on the recent advances on radiolysis-assisted shape-controlled synthesis of noble metal nanostructures. The techniques and protocols for producing desirable shapes of noble metal nanoparticles are discussed through introducing the critical parameters which can influence the nucleation and growth mechanisms. Nucleation rate plays a vital role on the crystallinity of seeds while growth rate of different seeds' facets determines the final shape of resultant nanoparticles. Nucleation and growth rate both can be altered with factors such as absorbed dose, capping agents, and experimental environment condition to control the final shape. Remarkable physical and chemical properties of synthesized noble metal nanoparticles by controlled morphology have been systematically evaluated to fully explore their applications.
  11. Adsorption and photocatalytic degradation of anionic dyes on Chitosan/PVA/Na-Titanate/TiO2 composites synthesized by solution casting method
    Habiba U, Islam MS, Siddique TA, Afifi AM, Ang BC
    Carbohydr Polym, 2016 09 20;149:317-31.
    PMID: 27261756 DOI: 10.1016/j.carbpol.2016.04.127
    Chitosan/PVA/Na-titanate/TiO2 composite was synthesized by solution casting method. The composite was analyzed via Fourier Transform Infrared Spectroscopy, X-ray diffraction, Field Emission Scanning Electron Microscopy, Thermal gravimetric analysis and water stability test. Incorporation of Na-titanate shown decrease of crystallinity for chitosan but increase water stability. However, the composite structure was deteriorated with considerable weight loss in acidic medium. Two anionic dyes, methyl orange and congo red were used for the adsorption test. The adsorption behavior of the composites were described by pseudo-second-order kinetic model and Lagergren-first-order model for methyl orange and congo red, respectively. For methyl orange, adsorption was started with a promising decolorization rate. 99.9% of methyl orange dye was removed by the composite having higher weightage of chitosan and crystalline TiO2 phase. On the other hand, for the congo red the composite having higher chitosan and Na-titanate showed an efficient removal capacity of 95.76%. UV-vis results showed that the molecular backbone of methyl orange and congo red was almost destroyed when equilibrium was obtained, and the decolorization rate was reaching 100%. Kinetic study results showed that the photocatalytic degradation of methyl orange and congo red could be explained by Langmuir-Hinshelwood model. Thus, chitosan/PVA/Na-titanate/TiO2 possesses efficient adsorptivity and photocatalytic property for dye degradation.
  12. Fulltext Selection of Mother Wavelet Functions for Multi-Channel EEG Signal Analysis during a Working Memory Task
    Al-Qazzaz NK, Bin Mohd Ali SH, Ahmad SA, Islam MS, Escudero J
    Sensors (Basel), 2015;15(11):29015-35.
    PMID: 26593918 DOI: 10.3390/s151129015
    We performed a comparative study to select the efficient mother wavelet (MWT) basis functions that optimally represent the signal characteristics of the electrical activity of the human brain during a working memory (WM) task recorded through electro-encephalography (EEG). Nineteen EEG electrodes were placed on the scalp following the 10-20 system. These electrodes were then grouped into five recording regions corresponding to the scalp area of the cerebral cortex. Sixty-second WM task data were recorded from ten control subjects. Forty-five MWT basis functions from orthogonal families were investigated. These functions included Daubechies (db1-db20), Symlets (sym1-sym20), and Coiflets (coif1-coif5). Using ANOVA, we determined the MWT basis functions with the most significant differences in the ability of the five scalp regions to maximize their cross-correlation with the EEG signals. The best results were obtained using "sym9" across the five scalp regions. Therefore, the most compatible MWT with the EEG signals should be selected to achieve wavelet denoising, decomposition, reconstruction, and sub-band feature extraction. This study provides a reference of the selection of efficient MWT basis functions.
  13. Effect of hydrolysed cellulose nanowhiskers on properties of montmorillonite/polylactic acid nanocomposites
    Arjmandi R, Hassan A, Haafiz MK, Zakaria Z, Islam MS
    Int J Biol Macromol, 2016 Jan;82:998-1010.
    PMID: 26592699 DOI: 10.1016/j.ijbiomac.2015.11.028
    Polylactic acid (PLA) nanocomposites reinforced with hybrid montmorillonite/cellulose nanowhiskers [MMT/CNW(SO4)] were prepared by solution casting. The CNW(SO4) nanofiller was first isolated from microcrystalline cellulose using acid hydrolysis treatment. PLA/MMT/CNW(SO4) hybrid nanocomposites were prepared by the addition of various amounts of CNW(SO4) [1-9 parts per hundred parts of polymer (phr)] into PLA/MMT nanocomposite at 5 phr MMT content, based on highest tensile strength values as reported previously. The biodegradability, thermal, tensile, morphological, water absorption and transparency properties of PLA/MMT/CNW(SO4) hybrid nanocomposites were investigated. The Biodegradability, thermal stability and crystallinity of hybrid nanocomposites increased compared to PLA/MMT nanocomposite and neat PLA. The highest tensile strength of hybrid nanocomposites was obtained by incorporating 1 phr CNW(SO4) [∼ 36 MPa]. Interestingly, the ductility of hybrid nanocomposites increased significantly by 87% at this formulation. The Young's modulus increased linearly with increasing CNW(SO4) content. This is due to the relatively good dispersion of nanofillers in the hybrid nanocomposites, as revealed by transmission electron microscopy. Fourier transform infrared spectroscopy indicated the formation of some polar interactions. In addition, water resistance of the hybrid nanocomposites improved and the visual transparency of neat PLA film did not affect by addition of CNW(SO4).
  14. Fulltext Management of mango hopper, Idioscopus clypealis, using chemical insecticides and Neem oil
    Adnan SM, Uddin MM, Alam MJ, Islam MS, Kashem MA, Rafii MY, et al.
    ScientificWorldJournal, 2014;2014:709614.
    PMID: 25140344 DOI: 10.1155/2014/709614
    An experiment was conducted in Field Laboratory, Department of Entomology at Bangladesh Agricultural University, Mymensingh, during 2013 to manage the mango hopper, Idioscopus clypealis L, using three chemical insecticides, Imidacloprid (0.3%), Endosulfan (0.5%), and Cypermethrin (0.4%), and natural Neem oil (3%) with three replications of each. All the treatments were significantly effective in managing mango hopper in comparison to the control. Imidacloprid showed the highest efficacy in percentage of reduction of hopper population (92.50 ± 9.02) at 72 hours after treatment in case of 2nd spray. It also showed the highest overall percentage of reduction (88.59 ± 8.64) of hopper population and less toxicity to natural enemies including green ant, spider, and lacewing of mango hopper. In case of biopesticide, azadirachtin based Neem oil was found effective against mango hopper as 48.35, 60.15, and 56.54% reduction after 24, 72, and 168 hours of spraying, respectively, which was comparable with Cypermethrin as there was no statistically significant difference after 168 hours of spray. Natural enemies were also higher after 1st and 2nd spray in case of Neem oil.
  15. Fulltext Role of EEG as biomarker in the early detection and classification of dementia
    Al-Qazzaz NK, Ali SH, Ahmad SA, Chellappan K, Islam MS, Escudero J
    ScientificWorldJournal, 2014;2014:906038.
    PMID: 25093211 DOI: 10.1155/2014/906038
    The early detection and classification of dementia are important clinical support tasks for medical practitioners in customizing patient treatment programs to better manage the development and progression of these diseases. Efforts are being made to diagnose these neurodegenerative disorders in the early stages. Indeed, early diagnosis helps patients to obtain the maximum treatment benefit before significant mental decline occurs. The use of electroencephalogram as a tool for the detection of changes in brain activities and clinical diagnosis is becoming increasingly popular for its capabilities in quantifying changes in brain degeneration in dementia. This paper reviews the role of electroencephalogram as a biomarker based on signal processing to detect dementia in early stages and classify its severity. The review starts with a discussion of dementia types and cognitive spectrum followed by the presentation of the effective preprocessing denoising to eliminate possible artifacts. It continues with a description of feature extraction by using linear and nonlinear techniques, and it ends with a brief explanation of vast variety of separation techniques to classify EEG signals. This paper also provides an idea from the most popular studies that may help in diagnosing dementia in early stages and classifying through electroencephalogram signal processing and analysis.
  16. Design and synthesis of mono and bicyclic tetrapeptides thioester as potent inhibitor of histone deacetylases
    Hoque MA, Islam MS, Islam MN, Kato T, Nishino N, Ito A, et al.
    Amino Acids, 2014 Oct;46(10):2435-44.
    PMID: 25048030 DOI: 10.1007/s00726-014-1800-5
    Inhibitors of histone deacetylases (HDACs) are a promising class of anticancer agents that have an effect on gene regulation. The naturally occurring cyclic depsipeptide FK228 containing disulfide and Largazole possessing thioester functionalities act as pro-drugs and share the same HDAC inhibition mechanism in cell. Inspired from these facts, we have reported bicyclic tetrapeptide disulfide HDAC inhibitors resembling FK228 with potent activity and enhanced selectivity. In the present study, we report the design and synthesis of several mono and bicyclic tetrapeptide thioester HDAC inhibitors that share the inhibition mechanism similar to Largazole. Most of the compounds showed HDAC1 and HDAC4 inhibition and p21 promoting activity in nanomolar ranges. Among these the monocyclic peptides 1, 2 and bicyclic peptide, 4 are notable demanding more advanced research to be promising anticancer drug candidates.
  17. Fulltext Effect of geometric parameters on the performance of p-type junctionless lateral gate transistors
    Larki F, Dehzangi A, Md Ali SH, Jalar A, Islam MS, Hamidon MN, et al.
    PLoS One, 2014;9(4):e95182.
    PMID: 24743692 DOI: 10.1371/journal.pone.0095182
    This paper examines the impact of two important geometrical parameters, namely the thickness and source/drain extensions on the performance of low doped p-type double lateral gate junctionless transistors (DGJLTs). The three dimensional Technology Computer-Aided Design simulation is implemented to calculate the characteristics of the devices with different thickness and source/drain extension and based on that, the parameters such as threshold voltage, transconductance and resistance in saturation region are analyzed. In addition, simulation results provide a physical explanation for the variation of device characteristics given by the variation of geometric parameters, mainly based on investigation of the electric field components and the carries density variation. It is shown that, the variation of the carrier density is the main factor which affects the characteristics of the device when the device's thickness is varied. However, the electric field is mainly responsible for variation of the characteristics when the source/drain extension is changed.
  18. Properties of polylactic acid composites reinforced with oil palm biomass microcrystalline cellulose
    Haafiz MK, Hassan A, Zakaria Z, Inuwa IM, Islam MS, Jawaid M
    Carbohydr Polym, 2013 Oct 15;98(1):139-45.
    PMID: 23987327 DOI: 10.1016/j.carbpol.2013.05.069
    In this work, polylactic acid (PLA) composites filled with microcrystalline cellulose (MCC) from oil palm biomass were successfully prepared through solution casting. Fourier transform infrared (FT-IR) spectroscopy indicates that there are no significant changes in the peak positions, suggesting that incorporation of MCC in PLA did not result in any significant change in chemical structure of PLA. Thermogravimetric analysis was conducted on the samples. The T50 decomposition temperature improved with addition of MCC, showing increase in thermal stability of the composites. The synthesized composites were characterized in terms of tensile properties. The Young's modulus increased by about 30%, while the tensile strength and elongation at break for composites decreased with addition of MCC. Scanning electron microscopy (SEM) of the composites fractured surface shows that the MCC remained as aggregates of crystalline cellulose. Atomic force microscopy (AFM) topographic image of the composite surfaces show clustering of MCC with uneven distribution.
  19. OSNR variation of multiple laser lines in Brillouin-Raman fiber laser
    Zamzuri AK, Mahdi MA, Al-Mansoori MH, Samsuri NM, Ahmad A, Islam MS
    Opt Express, 2009 Sep 14;17(19):16904-10.
    PMID: 19770907 DOI: 10.1364/OE.17.016904
    We report experimental results demonstrating the variation of optical signal-to-noise ratio (OSNR) of laser lines in Brillouin-Raman fiber laser against Raman pump power (RPP) variation. The reduction of OSNR is attributed to the spectral broadening of laser lines depending on the RPP. The spectral broadening is owing to the effect of the interaction between laser lines and turbulent waves (nonlinear interaction between longitudinal cavity modes). In our experiment, the worst OSNR is obtained at 650 mW RPP as a result of maximum spectral broadening when the Brillouin pump wavelength is fixed at 1555 nm. On the other hand, the OSNR improvement is obtained for RPP beyond 650 mW due to the effect of red-shift, the Raman peak gain is shifted away from the laser lines generated around 1555 nm thus reduces the spectral broadening effect.
  20. Fulltext Synthesis, molecular structure and spectroscopic investigations of novel fluorinated spiro heterocycles
    Islam MS, Al-Majid AM, Barakat A, Soliman SM, Ghabbour HA, Quah CK, et al.
    Molecules, 2015 May 07;20(5):8223-41.
    PMID: 25961163 DOI: 10.3390/molecules20058223
    This paper describes an efficient and regioselective method for the synthesis of novel fluorinated spiro-heterocycles in excellent yield by cascade [5+1] double Michael addition reactions. The compounds 7,11-bis(4-fluorophenyl)-2,4-dimethyl- 2,4-diazaspiro[5.5] undecane-1,3,5,9-tetraone (3a) and 2,4-dimethyl-7,11-bis (4-(trifluoromethyl)phenyl)-2,4-diazaspiro[5.5]undecane-1,3,5,9-tetraone (3b) were characterized by single-crystal X-ray diffraction, FT-IR and NMR techniques. The optimized geometrical parameters, infrared vibrational frequencies and NMR chemical shifts of the studied compounds have also been calculated using the density functional theory (DFT) method, using Becke-3-Lee-Yang-Parr functional and the 6-311G(d,p) basis set. There is good agreement between the experimentally determined structural parameters, vibrational frequencies and NMR chemical shifts of the studied compounds and those predicted theoretically. The calculated natural atomic charges using NBO method showed higher polarity of 3a compared to 3b.The calculated electronic spectra are also discussed based on the TD-DFT calculations.
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