A highly effective synthesis of 2-alkynyl-7-azaindoles: Pd/C-mediated alkynylation of heteroaryl halides in water

The reaction of 4-chloro-2-iodo-7-azaindole with terminal alkynes was investigated using 10% Pd/C-PPh₃-CuI as a catalyst system in water. This study afforded a new, mild and selective process for the preparation of 2-alkynyl-4-chloro-7-azaindole in good yields via C-C bond forming reaction. The resulting chloro derivative can be functionalized further via another Pd-mediated C-C bond forming reaction with arylboronic acid.     

Electronic Structure of InN/GaN Quantum Dots: Multimillion-Atom Tight-Binding Simulations

The theoretical calculation of the electronic structure of any constituent materials is the first step toward the interpretation and understanding of experimental data and reliable device design. This is essentially true for nanoscale devices where both the atomistic granularity of the underlying materials and the quantum-mechanical nature of charge carriers play critical roles in determining the overall device performance. In this paper, within a fully atomistic and quantum-mechanical framework, we investigate the electronic structure of wurtzite InN quantum dots (QDs) self-assembled on GaN substrates. The main objectives are threefold: 1) to explore the nature and the role of crystal atomicity, strain field, and piezoelectric and pyroelectric potentials in determining the energy spectrum and the wave functions; 2) to address the redshift in the ground state, the symmetry lowering and the nondegeneracy in the first excited state, and the strong band mixing in the overall conduction-band electronic states, which is a group of interrelated phenomena that has been revealed in recent spectroscopic analyses; and 3) to study the size dependence of the internal fields and its impact on the electronic structure as a whole. We also demonstrate the importance of 3-D atomistic material representation and the need for using realistically extended substrate and cap layers (multimillion-atom modeling) in studying the built-in structural and electric fields in these reduced dimensional QDs. The models used in this study are as follows: 1) valence-force-field Keating model for atomistic strain relaxation; 2) 20-band nearest neighbor sp ³ d ⁵ s* tight-binding model for the calculation of single-particle energy states; and 3) microscopically determined polarization constants in conjunction with an atomistic 3-D Poisson solver for the calculation of piezo- and pyroelectric contributions.     

Geometrical structure and nonlinear response variations of metal (M = Ni2+, Pd2+, Pt2+) octaphyrin complex derivatives: A DFT study

Nonlinear optical response of designed organometallic complexes of Ni²⁺, Pd²⁺, and Pt²⁺ metal ions with octaphyrin (OP) as ligand were explored by using DFT at CAM-B3LYP/6–311G++(d, p)/LANL2DZ/DEF2SV level of theory. The geometries of these organometallic complexes were studied in terms of effect on molecular framework by metal ion and substituent groups. The optimized geometry of free ligand displays that one of the four pyrrole rings orients out of plane to reduce the steric hindrance. The effect of the substituents on the geometry was found more prominent in the Ni²⁺-OP complexes. The calculations reveal enhancement in the values of dipole moment and hyperpolarizability on introducing electron withdrawing and electron donating groups in ligand framework with maximum enhancement in case of Pt²⁺-OP derivatives. In this study no regular trend was observed for the HOMO and LUMO energies with the second-order hyperpolarizability of M²⁺-OP complexes. However, we have observed that the excited-state properties calculated by using TD-DFT correlate well with the second-order hyperpolarizability values and the dependence was rationalized in terms of two-level model. Thus, from overall calculations we have observed that the designed organometallic complexes display higher polarizability and hyperpolarizability values and can be effective candidates for nonlinear response.     

Furan-containing conjugated polymers for organic solar cells

Development of organic semiconductors is one of the most intriguing and productive topics in material science and engineering. Many efforts have been made on the synthesis of aromatic building blocks such as benzene, thiophene and pyrrole due to the facile preparation accompanied by the intrinsic environmental stability and relatively efficient properties of the resulting polymers. In the past, furan has been less explored in this field because of its high oxidation potential. Recently, furan has attracted obsession due to its weaker aromaticity, the greater solubilities of furan-containing π-conjugated polymers relative to other benzenoid systems and the accessibility of furan-based starting materials from renewable resources. This review elaborates the advancements of organic photovoltaic polymers containing furan building blocks. The uniqueness and advantages of furan-containing building blocks in semiconducting materials are also discussed.     

Step and steady shear responses of nearly monodisperse highly entangled 1,4-polybutadiene solutions

Nonlinear relaxation dynamics of highly entangled solutions of high molecular weight 1,4-polybutadiene (PB) in a PB oligomer are studied in steady shear and step shear flows. Polymer entanglement densities vary in the range 14hN/N_e(J)⣴, allowing systematic investigation of entanglement effects on nonlinear rheological response. In agreement with previous steady shear studies using well entangled polystyrene solutions, a flow regime is found where both the steady-state shear stress and first normal stress difference remain constant or increase quite slowly with shear rate, leading to a plateau in the steady-state orientation angle. The magnitude of the average orientation angle in the plateau range is in accordance with predictions of a recent theory by Islam and Archer (2001). In step shear, the nonlinear relaxation modulus G(t,%) is approximately factorable into time-dependent G(t) and strain-dependent h(%) functions only at long times, t>5_k, where 5_k,O(F_d0). This finding is consistent with earlier observations for entangled polystyrene solutions; however the complex crossing pattern in G(t,%)h^-1(%) that precede factorability in the latter materials is not observed. For all but the most entangled sample, apparent shear damping functions h (%,t)=(G(t,%))/(G(t)) immediately following imposition of shear are in nearly quantitative accord with the damping function h_DEIA predicted by Doi-Edwards theory.     

Semiempirical evaluation of the global hardness of the atoms of 103 elements of the periodic table using the most probable radii as their size descriptors

Relying upon the fact that the density functional computation of the global hardness of the atoms of the elements are still at large and there is some mathematical in congruency between the theory and operational formula of finite difference approximation, we have suggested a radial‐dependent ansatz for evaluating global hardness of atoms as: η=a(7.2/r)+b (in eV), where, “a” and “b” are the constants and r is the absolute radius of atoms in angstrom unit. The ansatz is invoked to evaluate the global hardness of atoms of 103 element of the periodic table. The evaluated new set of global hardness is found to satisfy the sine qua non of a reasonable scale of hardness by exhibiting perfect periodicity of periods and groups and correlating the gross physicochemical properties of elements. The inertness of Hg and extreme reactivity Cs atoms are nicely correlated. The chemical reactivity and its variation in small steps in the series of lanthanide elements are also nicely reproduced. The results of the present semiempirical calculation also have strong correlation with the result of some sophisticated DFT calculation for a set of atoms. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Influence of accelerated ageing on the physico-mechanical properties of alkali-treated industrial hemp fibre reinforced poly(lactic acid) (PLA) composites

30 wt% aligned untreated long hemp fibre/PLA (AUL) and aligned alkali treated long hemp fibre/PLA (AAL) composites were produced by film stacking and subjected to accelerated ageing. Accelerated ageing was carried out using UV irradiation and water spray at 50 °C for four different time intervals (250, 500, 750 and 1000 h). After accelerated ageing, tensile strength (TS), flexural strength, Young's modulus (YM), flexural modulus and mode I fracture toughness (K_Ic) were found to decrease and impact strength (IS) was found to increase for both AUL and AAL composites. AUL composites had greatest overall reduction in mechanical properties than that for AAL composites upon exposure to accelerated ageing environment. FTIR analysis and crystallinity contents of the accelerated aged composites support the results of the deterioration of mechanical properties upon exposure to accelerated ageing environment.     

Coplanar Waveguide Fed Printed Antenna with Compact Size for Broadband Wireless Applications

A novel and simple coplanar waveguide fed compact antenna is introduced in this paper. The antenna structure combines the advantages of CPW with those of the broadband antenna and simplifies the structure of the antenna by reducing the number of metallization level to construct uni-planar antenna. Prototype of the proposed antenna have been constructed and studied experimentally. The measured results agrees well with the simulated prediction and shows a broad bandwidth of 6 GHz ranging from 3.5 GHz to 9.5 GHz with VSWR ≤2 (return loss ≤−10 dB), which is equivalent to 92.3% impedance bandwidth centered at 6.5 GHz. The proposed antenna shows stable radiation characteristics, gain and axial ratio of less than 1 dB over the whole operating bandwidth. Furthermore, an extensive parametric study was performed to realize the relationship between the resonance frequencies of the broadband antennas and different parameters which is helpful for advancement of the antenna design.     

Application of homomorphism to secure image sharing

In this paper, we present a new approach for sharing images between l players by exploiting the additive and multiplicative homomorphic properties of two well-known public key cryptosystems, i.e. RSA and Paillier. Contrary to the traditional schemes, the proposed approach employs secret sharing in a way that limits the influence of the dealer over the protocol and allows each player to participate with the help of his key-image. With the proposed approach, during the encryption step, each player encrypts his own key-image using the dealer's public key. The dealer encrypts the secret-to-be-shared image with the same public key and then, the l encrypted key-images plus the encrypted to-be shared image are multiplied homomorphically to get another encrypted image. After this step, the dealer can safely get a scrambled image which corresponds to the addition or multiplication of the l + 1 original images (l key-images plus the secret image) because of the additive homomorphic property of the Paillier algorithm or multiplicative homomorphic property of the RSA algorithm. When the l players want to extract the secret image, they do not need to use keys and the dealer has no role. Indeed, with our approach, to extract the secret image, the l players need only to subtract their own key-image with no specific order from the scrambled image. Thus, the proposed approach provides an opportunity to use operators like multiplication on encrypted images for the development of a secure privacy preserving protocol in the image domain. We show that it is still possible to extract a visible version of the secret image with only l-1 key-images (when one key-image is missing) or when the l key-images used for the extraction are different from the l original key-images due to a lossy compression for example. Experimental results and security analysis verify and prove that the proposed approach is secure from cryptographic viewpoint.