1,721,660 research outputs found
Design of LDPC Decoder for Error Correction in Memory Devices
No full textNAND flash memories are used in large number of electronic devices for storing data. The ever increasing demand of the high storage in these devices has resulted in high density NAND flash memories. The high density is achieved through the process of continuous technology scaling and the use of multilevel cell (MLC) technology. In multilevel cell technology more than one bits are stored in a single cell of the flash memory. However, this increased storage density has come at a price of reduced reliability. The raw bit error rate has increased rapidly in high density flash memories, therefore, demanding more powerful error correcting codes. The bit error rate (BER) requirements in NAND flash memories are reported to be 10^−13 to 10^−16, after applying the error correcting code. The current practice is to use the hard decision error correcting codes in NAND flash memories, such as BCH codes. However, as the raw bit error rate is getting worse, these hard decision codes will not be able to achieve the BER requirements of these memories. Therefore, more powerful error correcting codes with soft decision decoding algorithm are required. Among the soft decision codes, low density parity check codes (LDPC) can be a promising candidate for error correction in high density NAND flash memories due to their excellent error correction performance close to the Shannon limit. LDPC codes employed in NAND flash memories have large block lengths and very high code rate and should show good error correcting and error floor performance. Evaluating the error floor performance of these codes at very low frame error rates, typically around 10^−9 to 10^−10, require the use of high speed hardware simulators. Due to the reconfigurability and high speed, field programmable gate arrays (FPGAs) are largely used for evaluating the performance of LDPC codes. This thesis presents an FPGA based simulator system for evaluating the error correction and error floor performance of regular quasi cyclic (QC) LDPC Codes, for the application of large page size MLC NAND flash memories. Particularly, we targeted the algebraic QC-LDPC codes, which have high code rates and good error correcting and error floor performance. A generalized, high throughput and resource efficient hardware implementation of the QC-LDPC encoder and the decoder is given on FPGA. The proposed decoder can decode any regular QC-LDPC code including very high circulant weight QC-LDPC codes, such as euclidean geometry (EG) LDPC codes. The generalized and high throughput implementation of such large circulant weight QC-LDPC codes is not reported previously in the open literature. Moreover, the encoder and decoder hardware implementations are given on FPGA for very large page size (8 KB) of NAND flash memory, which are also not dealt previously in the open literature. A high speed and high quality floating point additive white Gaussian noise channel is implemented on FPGA using the high level synthesis method. The high level synthesis is used to rapidly prototype the channel on FPGA and to lower the development time of the LDPC simulator system. The very low consumption of the logic resources by the channel also enabled us to instantiate many channel modules in parallel, resulting in high throughput of the simulator. This thesis also presents the FPGA implementation and simulation results of two algebraic QC-LDPC codes for the page size 8 KB of NAND flash memory. Simulation results show good error correcting and error floor performance of the developed codes making them a promising candidate for error correction in NAND flash memorie
Electrochemical and photocatalytic oxidation of organic pollutants from waste water using efficient nano-catalytic coatings prepared by electrodeposition
No full textWastewater from the textile industry is considered to be one of the most pollutant effluents due to its toxic organic colourants content being strongly resistant to oxidation. When these substances are directly discharged into rivers and sea they persist for long periods causing environmental and aesthetic problems together with high health risks to living organisms. The main goal of this research is to study the oxidation of different textile dyes and organic pollutants, in particular reactive black-5 (RB-5) and methylene blue (MB) dyes using different nano catalytic coatings. A 3D flexible titanium felt electrode was anodized for growing TiO2 nanotubes and further decorated with PbO2 subsequently employed for anodic electrochemical and photochemical treatment of wastewater containing RB-5 dye. Similarly, reticulated vitreous carbon (RVC)surfaces were decorated with a layer of PbO2 and titanate nanosheets by anodic electrophoretic deposition, with subsequent structural and morphological characterization using FESEM and Raman spectroscopy. The TiNS/PbO2/RVC electrode has titanium anatase phase which was obtained by annealing at 450°C for 60 min in air. The structure revealed a well-specified, microporous structure with hydrophilic properties along the length and thickness of the RVC struts. Electrochemical and photocatalytic behaviour of the composite assisted the decolourisation of organic RB-5 dye in aqueous solution; on one hand • OH radicals were electrochemically produced via TiNS/PbO2/RVC anode composite coating and the photocatalytic decolourisation use the synergetic photocatalytic activity associated with the holes and free electron acceptors generated during UV irradiation experiments. Another objective of this thesis is the synthesis of efficient nanotubular titanates (TiNTs) coatings over the surface of the RVC substrate to make the organic oxidation more efficient. Titanate nanotubes (TiNTs) were deposited over the surface of a 100 pores per inch (ppi) RVC by anodic electrophoresis. The photocatalytic characteristics of the coating were enhanced by annealing at 450 °C for 60 min in air. A preliminary evaluation of novel TiNT/RVC coatings demonstrated to be useful for the photocatalytic colour removal of MB dye. In addition, a zinc metal plate was electrochemically anodised to produce ZnO nanowires. The selected operational conditions together a subsequent dip-coating process of the anodised ZnO surface in a TiO2 containing solution, produced a core-shell coating. A further electrochemical deposition of PbO2 over the core-shell produced a hybrid core (ZnO-TiO2)-shell (PbO2) coatings. The electrochemical and photocatalytic behaviour of the coatings were analysed by employing them to remove RB-5 dye (1 × 10-5 mol dm-3 ). The nano-coatings are low cost option for the oxidation of textile dyes and improved removal of RB-5 and MB dyes at a removal efficiency of ≈99 %
FPGA accelerator of algebraic quasi cyclic LDPC codes for NAND flash memories
Full text linkIn this article, the authors implement an FPGA simulator that accelerates the performance evaluation of very long QC-LDPC codes, and present a novel 8-KB LDPC code for NAND flash memory with better performance
Data for the paper entitled: Decolorization of Reactive Black-5 at an RVC substrate decorated with PbO2/ TiO2 nanosheets prepared by anodic electrodeposition
No full textData supports
S.Z.J. Zaidi, C. Harito, F.C. Walsh, C. Ponce de León (2018). Decolorization of Reactive Black-5 at an RVC substrate decorated with PbO2/ TiO2 nanosheets prepared by anodic electrodeposition. Journal of Solid State Electrochemistry
Reticulated vitreous carbon (RVC) substrates were coated with a composite of PbO2 and titanate nanosheets (TiNS) by anodic electrophoretic deposition. The structure and morphological characteristics of the coating were evaluated by Field Emission Scanning Electron Microscopy (FESEM) and Raman spectroscopy. The TiNS/PbO2/RVC coating contained the anatase phase and showed a well-defined, microporous morphology with hydrophilic character along the length and thickness of the RVC struts. Electrochemical and photocatalytic activity of the coatings facilitated RB-5 dye degradation as a model organic pollutant in wastewater. The electrochemical decolorization involves the generation of hydroxyl free radicals over the TiNS/PbO2/RVC anode composite surface whereas photocatalytic decolorization was driven by the synergetic photocatalytic effect imparted by the photoinduced holes and free electron acceptors. The photocatalytic properties of the TiNS/PbO2 coating were achieved by calcination at 450 °C for 60 minutes in air which converted the titanate phase to anatase and modified its surface area. This enabled 98 % electrochemical decolorization of the RB-5 dye solution (measured by visible absorption at 597 nm) in a time of 60 minutes.
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Decolourisation of reactive black-5 at an RVC substrate decorated with PbO2/ TiO2 nanosheets prepared by anodic electrodeposition
No full textReticulated vitreous carbon (RVC) substrates were coated with a composite of PbO2 and titanate nanosheets (TiNS) by electrophoresis. The structure and morphological characteristics of the coating were evaluated by field emission scanning electron microscopy (FESEM) and Raman spectroscopy. The TiNS/PbO2/RVC coating contained the anatase phase and showed a well-defined, microporous morphology with hydrophilic character along the length and thickness of the RVC struts. Electrochemical and photocatalytic activity of the coatings facilitated RB-5 dye degradation as a model organic pollutant in wastewater. The electrochemical decolourisation involves the generation of hydroxyl free radicals over the TiNS/PbO2/RVC anode composite surface whereas photocatalytic decolourisation was driven by the synergetic photocatalytic effect imparted by the photoinduced holes and free electron acceptors. The photocatalytic properties of the TiNS/PbO2 coating were achieved by calcination at 450 °C for 60 minutes in air which converted the titanate phase to anatase and modified its surface area. This enabled 98% decolourisation of the RB-5 dye solution (measured by visible absorption at 597 nm) in a time of 60 minutes
Biogenic nanoparticles: synthesis, characterisation and applications
Full text linkNanotechnology plays a big part in our modern daily lives, ranging from the biomedical sector to the energy sector. There are different physicochemical and biological methods to synthesise nanoparticles towards multiple applications. Biogenic production of nanoparticles through the utilisation of microorganisms provides great advantages over other techniques and is increasingly being explored. This review examines the process of the biogenic synthesis of nanoparticles mediated by microorganisms such as bacteria, fungi and algae, and their applications. Microorganisms offer a disparate environment for nanoparticle synthesis. Optimum production and minimum time to obtain the desired size and shape, to improve the stability of nanoparticles and to optimise specific microorganisms for specific applications are the challenges to address, however. Numerous applications of biogenic nanoparticles in medicine, environment, drug delivery and biochemical sensors are discussed.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Risk Assessment of Ambient Air Pollutants and Health Impact around Fuel Stations in Urban Cities of KSA
Full text linkAbstract
Background: In Saudi Arabia, fuel dispensing facilities commonly present around the residential
places, educational institutions, and various health care facilities. Fuel pollutants such as benzene,
toluene, and xylenes (BTX) and its alkyl derivatives are harmful to human health because of their
toxic, mutagenic, or carcinogenic properties. The aim of this study was to determine the BTX
concentration levels of common pollutants in and around fuel stations and their harmful health effects
in the urban cites of KSA. Methods: Forty fuel dispensing facilities were randomly selected on the
basis of three different areas: residential, traffic intersection, and petrol pump locations (refueling
stations). Portable ambient analyzer was used for measuring BTX concentration. t‑test was applied
to determine the difference between these different areas. Results: All mean concentration values
of pollutants such as BTX around residential, traffic intersection, and fuel stations are exceeding
the limits of air quality standards values (P < 0.01). The mean levels of benzene are 10.3 and 11.07
ppm in Dammam and Khobar, respectively, and they exceed the reference level of 0.5 ppm. Hazard
quotient was more than >1, which shows that carcinogenic probability has increased those who were
living and working near fuel stations. Conclusions: The results found that the high concentration
of pollutants (BTX) is in the environment around fuel stations. The environmental contamination
associated with BTX in petrol fuel stations impulses the necessity of preventive programs to reduce
the further air quality deterioration and reduce the harmful health effects.
Keywords: Air, benzene, fuel, pollution, toluene, xylene
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