Detecting DDoS Attacks in Cloud Computing Using Extreme Learning Machine and Adaptive Differential Evolution

Wireless Personal Communications - Distributed denial of service (DDoS) attacks disrupt the availability of cloud services. The detection of these attacks is a major challenge in the cloud...     

Synthesis of CuTi-LDH supported on g-C3N4 for electrochemical and photoelectrochemical oxygen evolution reactions

A nanocomposite CuTi layered double hydroxide (LDH) supported on g-C₃N₄ (15 wt% of g-C₃N₄) is facilely synthesized by hydrothermal method. There are electrostatic interactions between positive layers of CuTi-LDH and negatively charged inner g-C₃N₄ sheets. The nanocomposite and its precursors are characterized through various analytical techniques, which affirmed the presence of both g-C₃N₄ and CuTi-LDH characteristic features. The pore-enriched hybrid geometry of CuTi-LDH@g-C₃N₄ with high specific surface area (146 m²/g), and suitable band gap of 2.46 eV enables the nanocomposite to act as both an electrocatalyst and photoelectrocatalyst for oxygen evolution reaction (OER). Both the electrochemical and photoelectrochemical studies are done using 1 M KOH (pH = 13.6) with applied potential of ?0.2 V to 1.5 V vs. Ag/AgCl. The onset potential of CuTi-LDH@g-C₃N₄ for OER appears at η = 0.36 V in dark and η = 0.32 V under visible light illumination of 30 min. Also, Mott-Schottky analysis shows n-type semiconductor behaviour for CuTi-LDH@g-C₃N₄ and its precursors. The photoelectrochemical water oxidation proceeds by charge transfer across a Type II heterojunction formed between the CuTi-LDH and g-C₃N₄ materials.     

Nitrogen doped mesoporous carbon supported Pt electrocatalyst for oxygen reduction reaction in proton exchange membrane fuel cells

Nitrogen doped mesoporous carbons are employed as supports for efficient electrocatalysts for oxygen reduction reaction. Heteroatom doped carbons favour the adsorption and reduction of molecular oxygen on Pt sites. In the present work, nitrogen doped mesoporous carbons (NMCs) with variable nitrogen content were synthesized via colloidal silica assisted sol-gel process with Ludox-AS40 (40 wt% SiO₂) as hard template using melamine and phenol as nitrogen and carbon precursors, respectively. The NMC were used as supports to prepare Pt/NMC electrocatalysts. The physicochemical properties of these materials were studied by SEM, TEM, XRD, BET, TGA, Raman, XPS and FTIR. The surface areas of 11 wt% (NMC-1) and 6 wt% (NMC-2) nitrogen doped mesoporous carbons are 609 m² g^?1 and 736 m² g^?1, respectively. The estimated electrochemical surface areas for Pt/NMC-1 and Pt/NMC-2 are 73 m² g^?1 and 59 m² g^?1, respectively. It is found that Pt/NMC-1 has higher ORR activity with higher limiting current and 44 mV positive onset potential shift compared to Pt/NMC-2. Further, the fuel cell assembled with Pt/NMC-1 as cathode catalyst delivered 1.8 times higher power density than Pt/NMC-2. It is proposed that higher nitrogen content and large pyridinic nitrogen sites present in NMC-1 support are responsible for higher ORR activity of Pt/NMC-1 and high power density of the fuel cell using Pt/NMC-1 cathode electrocatalyst. The carbon support material with high pyridinic content promotes the Pt dispersion with particle size less than 2 nm.     

Waste-to-wealth approach in water economy: The case of beneficiation of mercury-contaminated water in hydrogen production

Heavy metals (Hg, Cd, Pb, etc.) are micro-pollutants and result in water contamination. Significant bio-concentration of heavy metal like Hg can lead to fatal disease such as Minamata. Given this context, heavy metal removal from wastewater is essential before discharge. The wastewater treatment process requires considerable amount of energy which is being met by the conventional carbon-based fuels. This contributes to the global carbon dioxide emission, and hence global warming. Therefore, if clean energy sourcing is enabled during the treatment of the wastewater; it would offer obvious advantages. If the energy production is ‘clean’ and achieved via the process itself, it would serve two outcomes: (a) meeting the energy demand for wastewater treatment, and (b) getting rid of the need for external ‘carbon-based’ energy. Recently a few research articles have reported simultaneous clean energy production from wastewater during its treatment. Thus, the energy demand of the wastewater treatment process can be potentially met with the clean energy produced during the process. In this review, we will discuss mercury-contaminated wastewater treatment with simultaneous hydrogen production. We will provide a brief overview of waste-to-wealth approaches currently prevailing in water economy, recent mercury removal processes, and discuss future possibilities of self-sustained Hg-contaminated wastewater treatment.     

Micro and nano-architectures of Co3O4 on Ni foam for electro-oxidation of methanol

Spinel Co₃O₄ material with different morphologies is directly grown on Ni foam by simple hydrothermal method and subsequent calcination processes. The direct growth of binder free active phase of Co₃O₄ on Ni foam is an effective approach to enhance the electrocatalytic activity of the material. The morphologies of Co₃O₄ strongly depend on the anion of the precursor salt used. Microflowers, microspheres and nanograss morphologies of Co₃O₄ are obtained using chloride, sulfate and acetate salts of cobalt, respectively. The BET surface areas of these cobalt oxide materials are found to increase in the order of microflower-Co₃O₄ (53 m² g^?1) < nanograss-Co₃O₄ (65 m² g^?1) < microsphere-Co₃O₄ (100 m² g^?1). The electrocatalytic activity of these Co₃O₄ materials has been tested for methanol oxidation by cyclic voltammetry and chronoamperometry. All three samples show low onset potentials (0.32–0.34 V) for methanol oxidation. The vanodic peak current of methanol oxidation is found to increase in the order of microflower-Co₃O₄ (28 A g^?1) < nanograss-Co₃O₄ (34.9 A g^?1) < microsphere-Co₃O₄ (36.2 A g^?1) at 0.6 V. This study highlights the significance of the morphology of cobalt oxide in the development of oxide based non-precious electrocatalysts for methanol oxidation.     

Bismuth oxycarbonate grafted NiFe-LDH supported on g-C3N4 as bifunctional catalyst for photoelectrochemical water splitting

In the present study, we report the synthesis of photoactive bismuth oxycarbonate (BOC, Bi₂O₂CO₃) grafted NiFe layered double hydroxide (LDH) supported on g-C₃N₄ (15 wt% of g-C₃N₄) by coprecipitation method. The band gap of this photoactive material is determined to be 1.7 eV. The Bi₂O₂CO₃ agglomerates are anchored on NiFe-LDH plates and g-C₃N₄ nanosheets intercalated between the LDH plates. This architecture helps in expediting electron transfer for hydrogen and oxygen evolution reactions. The pristine NiFe-LDH photoanode acquires bifunctional character because of Bi₂O₂CO₃ agglomerates and g-C₃N₄ embedded in the architecture of BOC/NiFe-LDH@g-C₃N₄. This is found to be an efficient photoanode for oxygen evolution and photocathode for hydrogen evolution reactions. The water splitting process occurs along the heterojunction formed between g-C₃N₄ nanosheets and Bi₂O₂CO₃ grafted NiFe-LDH. Further, an additional interfacial charge transfer aided by Bi₂O₂CO₃ results in S-scheme mechanism, which enhances the rate of photoelectrochemical hydrogen and oxygen evolution reactions.     

Electric-field-induced self-assembled one-dimensional nanostructures in CdX and HgX (X=Se, Te) thin films

Self-assembling due to the presence of electric field during deposition in the spray deposited nanocrystalline CdX and HgX (X=Se and Te) thin films is reported. The films are deposited using solvothermally synthesized nanoparticles dispersed in 1-butanol and sprayed on the glass substrates at 200 °C without any voltage as well as by applying a voltage to the nozzle. The electron microscopy studies reveal the formation of nanorods for the films deposited with the voltage. The X-ray diffractograms of CdSe films deposited without voltage and with voltage show hexagonal crystal structure. On the other hand, CdTe films deposited without voltage show cubic crystal structure and the films deposited with voltage show hexagonal crystal structure. HgX films deposited without and with voltage show cubic crystal structure and there is no nanorod formation below 700 V. HRTEM studies show the growth direction of the CdX nanostructures. In view of the self-assembly observed under voltage, the induced dipole moment and the resultant electrostatic interaction are expected to be the driving force for the growth of nanorods. Blueshift in the band gap is observed for all the films deposited without and with voltages, and it is attributed to the quantum confinement effect due to the formation self-assembled one-dimensional nanostructures.     

Study of jet precession, recirculation and vortex breakdown in turbulent swirling jets using LES

Large eddy simulations (LES) are used to investigate turbulent isothermal swirling flows with a strong emphasis on vortex breakdown, recirculation and instability behaviour. The Sydney swirl burner configuration is used for all simulated test cases from low to high swirl and Reynolds numbers. The governing equations for continuity and momentum are solved on a structured Cartesian grid, and a Smagorinsky eddy viscosity model with the localised dynamic procedure is used as the sub-grid scale turbulence model. The LES successfully predicts both the upstream first recirculation zone generated by the bluff body and the downstream vortex breakdown bubble. The frequency spectrum indicates the presence of low frequency oscillations and the existence of a central jet precession as observed in experiments. The LES calculations well captured the distinct precession frequencies. The results also highlight the precession mode of instability in the center jet and the oscillations of the central jet precession, which forms a precessing vortex core. The study further highlights the predictive capabilities of LES on unsteady oscillations of turbulent swirling flow fields and provides a good framework for complex instability investigations.     

Design-Space Exploration for Block-Processing Based Temporal Partitioning of Run-Time Reconfigurable Systems

The reconfiguration capability of modern FPGA devices can be utilized to execute an application by partitioning it into multiple segments such that each segment is executed one after the other on the device. This division of an application into multiple reconfigurable segments is called temporal partitioning. We present an automated temporal partitioning technique for acyclic behavior level task graphs. To be effective, any behavior-level partitioning method should ensure that each temporal partition meets the underlying resource constraints. For this, a knowledge of the implementation cost of each task on the hardware should be known. Since multiple implementations of a task that differ in area and delay are possible, we perform design-space exploration to choose the best implementation of a task from among the available implementations.To overcome the high reconfiguration overhead of the current day FPGA devices, we propose integration of the temporal partitioning and design space exploration methodology with block-processing. Block-processing is used to process multiple blocks of data on each temporal partition so as to amortize the reconfiguration time. We focus on applications that can be represented as task graphs that have to be executed many times over a large set of input data. We have integrated block-processing in the temporal partitioning framework so that it also influences the design point selection for each task. However, this does not exclude usage of our system for designs for which block-processing is not possible. For both block-processing and non block-processing designs our algorithm selects the best possible design point to minimize the execution time of the design.We present an ILP-based methodology for the integrated temporal partitioning, design space exploration and block-processing technique that is solved to optimality for small sized design problems and in an iterative constraint satisfaction approach for large sized design problems. We demonstrate with extensive experimental results for the Discrete Cosine Transform (DCT) and random graphs the validity of our approach.     

Snake pedals: compact and versatile geometric models withphysics-based control

We introduce a geometric shape modeling scheme which allows for representation of global and local shape characteristics of an object. Geometric models are well-suited for representing global shapes without local detail, but we propose a scheme which represents global shapes with local detail and permits model shaping as well as topological changes via physics-based control. The scheme represents shapes by pedal curves and surfaces, i.e. the loci of the foot of perpendiculars to the tangents of a fixed curve/surface from a fixed point called the pedal point. By varying the location of the pedal point, one can synthesize a large class of shapes which exhibit both local and global deformations. We introduce physics-based control for shaping these geometric models by letting the pedal point vary and use a snake to represent the position of this varying point. The model, a “snake pedal”, allows for interactive manipulation via forces applied to the snake. We develop a fast numerical iterative algorithm for shape recovery from image data using this scheme. The algorithm involves the Levenberg-Marquardt (LM) method in the outer loop for solving the global parameters and the alternating direction implicit (ADI) method in the inner loop for solving the local parameters of the model. The combination of the global and local scheme leads to an efficient numerical solution to the model fitting problem. We demonstrate the applicability of this modeling scheme via examples of shape synthesis and shape estimation from real image data