Chemical synthesis of zinc oxide nanorods for enhanced hydrogen gas sensing

Zinc oxide(ZnO) nanorods are prepared using equimolar solution of zinc nitrate((Zn(NO3)2) and hexamethylenetetramine(C6H12N4) by the hydrothermal technique at 80 C for 12 h. Epitaxial growth is explored by X-ray diffraction(XRD) patterns, revealing that the ZnO nanorods have a hexagonal(wurtzite) structure. Absorption spectra of ZnO are measured by UV–visible spectrometer. The surface morphology is investigated by field emission scanning electron microscopy(FESEM). The synthesized ZnO nanorods are used for detecting the 150 C hydrogen gas with a concentration over 1000 ppm. The obtained results show a reversible response. The influence of operating temperature on hydrogen gas detecting characteristic of ZnO nanorods is also investigated.     

First Principles Investigation of Fluorine Based Strontium Series of Perovskites

Density functional theory is used to explore structural, elastic, and mechanical properties of SrLiF₃, SrNaF₃, SrKF₃ and SrRbF₃ fluoroperovskite compounds by means of an ab-initio Full Potential-Linearized Augmented Plane Wave (FP-LAPW) method. Several lattice parameters are employed to obtain accurate equilibrium volume (V_o). The resultant quantities include ground state energy, elastic constants, shear modulus, bulk modulus, young's modulus, cauchy's pressure, poisson's ratio, shear constant, ratio of elastic anisotropy factor, kleinman's parameter, melting temperature, and lame's coefficient. The calculated structural parameters via DFT as well as analytical methods are found to be consistent with experimental findings. Chemical bonding is used to investigate corresponding chemical trends which authenticate combination of covalent-ionic behavior. Furthermore electron density plots as well as elastic and mechanical properties are reported for the first time which reveals that fluorine based strontium series of perovskites are mechanically stable and posses weak resistance towards shear deformation as compared to resistance towards unidirectional compression while brittleness and ionic behavior is dominated in them which decreases from SrLiF₃ to SrRbF₃. Calculated cauchy's pressure, poisson's ratio and B/G ratio also proves ionic nature in these compounds. The present methodology represents an effective and influential approach to calculate the whole set of elastic and mechanical parameters which would support to understand various physical phenomena and empower device engineers for implementing these materials in numerous applications.     

Kinetics and mechanism of the cleavage of n-methoxyphthalimide (NMPT) in the presence of buffers of tris (hydroxymethyl)amino methane (tris) and 1,4-diazabicyclo[2.2.2]octane (DABCO)

The magnitude of hydroxide ion-catalyzed second-order rate constant (k_OH) for hydrolysis of N-methoxyphthalimide (NMPT) supports the conclusion that the rate law for pH-independent hydrolysis of N-hydroxyphthalimide (NHPTH) is rate = k_OH[HO^-][SH] where SH represents nonionized NHPTH. The second-order rate constants for the reactions of NMPT with DABCO and Tris are (59.7 ± 6.9) x 10^-3 and (11.9 ± 2.3) x 10^-4 M^-1 s^-1, respectively. This revised version was published online in June 2006 with corrections to the Cover Date.     

Structure determination of ramosine, a guaianolide, by NMR spectroscopy

Ramosine, a new sesquiterpene lactone, was isolated from the chloroform fraction of Amberboa ramosa and the structure was assigned as 4beta-(hydroxymethyl)-3beta,4alpha-dihydroxy-8alpha-[(S)-3-hydroxy-2-ethylenepropionyloxy]-1alphaH, 5alphaH,6betaH,7alphaH,11betaH,11alpha-methylguaia-10(14)-en-6, 12-olide by extensive NMR studies.     

Radiometric analysis of rock and soil samples of Leepa Valley; Azad Kashmir, Pakistan

In this article, we present results obtained from a radiometric survey that was conducted in the Leepa Valley of Azad Jammu & Kashmir, Pakistan. The purpose of current study is to appraise the radioactivity levels and the associated health hazards due to the terrestrial radionuclide in soil and rock samples. In this regard, 16 soil and 17 rock samples were collected from different locations of the Leepa Valley. After processing the samples, activity concentrations of primordial (²³²Th, ²²⁶Ra and ⁴⁰K) and anthropogenic (¹³⁷Cs) radionuclides were determined using a P-type coaxial high purity germanium detector. From the results obtained the mean activity concentrations of radionuclides ²²⁶Ra, ²³²Th and ⁴⁰K in the soil samples were found to be 31.25 ± 0.46, 44.1 ± 1.07 and 575 ± 8.89 Bq kg^?1 respectively. Whilst, in rock samples ²²⁶Ra, ²³²Th and ⁴⁰K mean activities were found as 28.46 ± 0.45, 48.63 ± 1.12 and 666.7 ± 9.39 Bq kg^?1, respectively. The ¹³⁷Cs concentration level in soil and rock samples is found to be 15.04 ± 0.29 and 5.7 ± 0.16 Bq kg^?1, respectively. The average radium equivalent activity (R _aeq) was found as 143.16 and 142.93 Bq kg^?1 in soil and rock samples, respectively. These findings are less than the recommended safe value of 370 Bq kg^?1 as given in OECD report (1979). The values of external (H _ex) and internal hazard index (H _in) are also less than unity. Mean value of absorbed dose rate was found as 69.78 nGy h^?1 for the soil samples, which is in good agreement with the world wide average value (70 nGy h^?1). Mean value of absorbed dose rate from rock samples was found as 70.01 nGy h^?1. Mean values of the annual effective dose is also lower than the values reported for different other countries of the world.     

Numerical approach for stagnation point flow of Sutterby fluid impinging to Cattaneo–Christov heat flux model

This paper presents a comprehensive modelling and simulation study on the optimum parameters that control the distortion and noise of semiconductor lasers (SLs) subject to multichannel modulation for use in analog cable television (CATV) fibre links. The study is based on numerical integration of the rate equation model of the semiconductor laser. The parameters comprise the modulation index per channel (m / ch), number of loaded channels (N) and fibre length \((L_{F})\). The signal distortions include the composite second-order (CSO) and composite triple beat (CTB) distortions. The noise is assessed in terms of the relative intensity noise (RIN) and carrier-to-noise ratio (CNR). In order to achieve acceptable CNR values for SL, m / ch should be less than 7.5 and 2% when loading 12 and 80 channels, respectively. For the CATV fibre link with \(L_{F} = 10 \hbox { km}\), the increase in the number of channels from 12 to 80 corresponds to lowering the optimum value of m / ch from 7 to 1%. The increase of \(L_{F}\) to 50 km limits the optimum value of m / ch between 1.4 and 1%, which corresponds to loading between 12 and 17 channels only.     

A Novel Image Encryption Scheme Based on Elliptic Curves over Finite Rings

Image encryption based on elliptic curves (ECs) is emerging as a new trend in cryptography because it provides high security with a relatively smaller key size when compared with well-known cryptosystems. Recently, it has been shown that the cryptosystems based on ECs over finite rings may provide better security because they require the computational cost for solving the factorization problem and the discrete logarithm problem. Motivated by this fact, we proposed a novel image encryption scheme based on ECs over finite rings. There are three main steps in our scheme, where, in the first step, we mask the plain image using points of an EC over a finite ring. In step two, we create diffusion in the masked image with a mapping from the EC over the finite ring to the EC over the finite field. To create high confusion in the plain text, we generated a substitution box (S-box) based on the ordered EC, which is then used to permute the pixels of the diffused image to obtain a cipher image. With computational experiments, we showed that the proposed cryptosystem has higher security against linear, differential, and statistical attacks than the existing cryptosystems. Furthermore, the average encryption time for color images is lower than other existing schemes.     

Light-Responsive Polyblend Films with Reconfigurable Surface Micropatterns as Rewritable Information Storage Media

Stimulus-sensitive surfaces with tunable morphologies exhibit a wide range of applications in the fields of surface science and engineering. Herein, a cost-effective yet practical strategy is proposed to fabricate photo-sensitive patterning surface on film/substrate wrinkle system based on an azo-containing polyblend. By manipulating the stress field of the bilayer system globally and/or locally upon the stress relaxation triggered by the reversible cis-trans isomerization of the azobenzene, heating/cooling triggered surface wrinkles on the polyblend films could be tailor-made with visible-light-irradiation. Notably, upon selective photo-irradiation, bespoke surface patterns may be cyclically generated or eliminated, allowing these reconfigurable patterned polyblend surfaces to be used as rewritable information storage media for non-ink printing. The as-prepared photo-printed information patterns with high-resolution are shown to be rewritable for multiple cycles and legible for over 90 d in dark ambient conditions. This study not only provides a versatile strategy for flourishing the stimulus-sensitive systems, but also sheds light on the stress relaxation-triggered morphological evolution of the wrinkling polyblend films.