Thermal properties of silicate esters

Fourteen dimethyldialkoxysilanes are prepared by reacting dimethyldichlorosilane with corresponding alcohols in the liquid phase. Their physicochemical properties are determined by standard methods and their tentative empirical formulae are elucidated. The thermal conductivity values of dimethyldialkoxysilanes are determined using a two slab guarded hot plate apparatus over a temperature range of 30–190°C. The thermal conductivity values of dimethyldialkoxysilanes calculated from empirical equations are found to vary from -14% to +19%. Because thermal conductivity is an important parameter in heat transfer calculations, and to minimise the deviation of the values, new equations involving easily measurable ultrasonic parameters have been formulated. The proposed equations have been tested for the series of dimethyldialkoxysilanes, tetraalkoxysilanes and polydimethylsiloxanes. The thermal conductivity values computed from the proposed equations are comparable with experimental thermal conductivity values. Further, an equation involving the calculation of thermal conductivity values at varying temperatures is also proposed.     

High-performance thin layer chromatographic method for quantitative determination of curcuminoids in Curcuma longa germplasm

Phytochemical investigation of the rhizomes of Curcuma longa leads to the isolation of pharmacologically active curcuminoids viz Curcumin, demethoxycurcumin and bisdemethoxycurcumin. These were isolated from turmeric rhizomes by soxhlet extraction followed by column chromatography, crystallisation and identified by spectroscopic studies. The purity of the curcuminoids was analysed by HPTLC method. The method employed TLC aluminium plates precoated with silica gel 60GF₂₅₄ as the stationary phase. The solvent system consisted of chloroform: methanol (48:2, v/v). This system was found to give compact spots for curcumin, demethoxycurcumin and bisdemethoxycurcumin (R_F value of 0.66 ± 0.02, 0.48 ± 0.02 and 0.30 ± 0.02), respectively. Densitometric analysis of curcuminoids was carried out in the absorption–reflection detection mode at 425 nm. Seven different germplasm of turmeric were analysed to detect the percentage of these three curcuminoids.     

An Efficient Privacy-Preserving ID Centric Authentication in IoT Based Cloud Servers for Sustainable Smart Cities

Wireless Personal Communications - Smart cities or Smart societies require Internet of Things (IoT), for connecting numerous devices to enormous asset pools in cloud computing. This coordination of...     

A two-level authentication scheme for clone node detection in smart cities using Internet of things

Clone node attack in IoT sensor devices remains a grave security concern as it paves the way for sinkhole, wormhole, and selective forwarding attacks. In this paper, a two-level authentication scheme named Fingerprint-based Zero-Knowledge Authentication (FZKA) algorithm is proposed to improve the detection rate of clone node among the sensor devices. In the fingerprint generation phase, the base station calculates a distinct fingerprint value for each and every node in the network by gathering neighborhood information, represented in the form of superimposed s-disjunct code matrix. The calculated fingerprint is considered as a secret value and distributed to each cluster nodes for the process of authentication. The FZKA algorithm improves the cloned node detection accuracy with minimal detection time. The simulation results highlight the cloned node detection rate of the proposed scheme by a margin of 92.5% against the existing Exponential Smoothing Algorithm (ETS), Position Verification Method, and Message Verification and Passing algorithms.     

An Efficient Optimized Handover in Cognitive Radio Networks Using Cooperative Spectrum Sensing

Cognitive radio systems necessitate the incorporation of cooperative spectrum sensing among cognitive users to increase the reliability of detection. We have found that cooperative spectrum sensing is not only advantageous, but is also essential to avoid interference with any primary users. Interference by licensed users becomes a chief concern and issue, which affects primary as well as secondary users leading to restrictions in spectrum sensing in cognitive radios. When the number of cognitive users increases, the overheads of the systems, which are meant to report the sensing results to the common receiver, which becomes massive. When the spectrum, which is in use becomes unavailable or when the licensed user takes the allocated band, these networks have the capability of changing their operating frequencies. In addition, cognitive radio networks are seen to have the unique capability of sensing the spectrum range and detecting any spectrum, which has been left underutilized. Further this capability of recognizing the spectrum range based on the dimensions detected, allows for determination of the band, which may be utilized. The main objective of this paper is to analyze the cognitive radio’s spectrum sensing ability and evolving a self-configured system with dynamic intelligence networks without causing any interference to the primary user. The paper also brings focus to the quantitative analysis of the two spectrum sensing techniques namely; Energy Detection and Band Limited White Noise Detection. The estimation technique for detecting spectrum noise is based on the detection of probability and probability of false alarms at different Signal-to-Noise Ratio (SNR) levels using Additive White Gaussian Noise signal (AWGN). The efficiency of the proposed Cooperative CUSUM spectrum sensing algorithm performs better than existing optimal rules based on a single observation spectrum sensing techniques under cooperative networks.     

Electrochemical synthesis of self-organized TiO2 nanotubular structures using an ionic liquid (BMIM-BF4)

We show that an ionic liquid consisting of imidazolium salt with a BF₄ counter ion (BMIM-BF₄) can directly be used to grow well-defined layers of self-organized TiO₂ nanotubes. For this a Ti metal substrate is anodized in this electrolyte for potential range between 3 V_Ag/AgCl and 10 V_Ag/AgCl without addition of free fluoride species (fluorides are used in all previous tube growth procedures). Key factors that influence the morphology and geometry of the resulting nanotubular layer are the anodic potential, the anodization time and particularly the water content in the ionic liquid. The resulting nanotubes layers have thickness in the range of approximately 300-650 nm; with individual tubes that have diameters between 27 nm and 43 nm.     

Free vibrations of square plantes with stiffened square openings

A grid frame work model is extended to obtain the natural frequencies of square plates with stiffened square openings. This technique eliminates the use of fictitious points at the re-entrant corner point, junction point, etc. on the stiffened opening. Numerical results are presented for the first time for the cases of plates with simply supported and clamped boundary conditions in order to show the convergence and versatility of the method. Also, this investigation provides a general feeling about the changes in fundamental frequencies that occur when stiffeners are introduced.