Influence of DC electric field on the Lennard-Jones potential and phonon vibrations of carbon nanotube on catalyst

Influence of DC electric field on carbon nanotube (CNT) growth in chemical vapor deposition is studied. Investigation of electric field effect in van der Waals interaction shows that increase in DC electric field raises the magnitude of attractive term of the Lennard-Jones potential. By using a theoretical model based on phonon vibrations of CNT on catalyst, it is shown that there is an optimum field for growth. Also it is observed that CNT under optimum electric field is longer than CNT in the absence of field. Finally, the relation between optimum DC electric field and type of catalyst is investigated and for some intervals of electric field, the best catalyst is introduced, which is very useful for experimental researches.     

Sonochemical synthesis of hierarchical ZnO nanostructures

This work is about fabrication of ZnO nanostructures (ZnO-NS) via a simple sonochemical method. The chemicals used for the synthesis of various shaped ZnO are Zn salt, sodium hydroxide and ammonia solution without other structure directing agent or surfactant needed. This method is feasible and green, as it does not require high temperature and/or highly toxic chemicals. The shape of the ZnO-NS can be tuned by adjusting the ultrasound energy dissipated via varying the ultrasonication time from 5 to 60 min. It was found that uniform ZnO nanorods with diameter around 50 nm were formed after 15 min of ultrasonication while flowerlike ZnO-NS was formed after 30 min. This method produces high quality ZnO-NS with controllable shapes, uniformity, and purity.     

Relativistic symmetries in the Rosen-Morse potential and tensor interaction using the Nikiforov-Uvarov method

Approximate analytical bound-state solutions of the Dirac particle in the fields of attractive and repulsive Rosen- Morse (RM) potentials including the Coulomb-like tensor (CLT) potential are obtained for arbitrary spin-orbit quantum number κ. The Pekeris approximation is used to deal with the spin-orbit coupling terms κ(κ± 1)r 2 . In the presence of exact spin and pseudospin (p-spin) symmetries, the energy eigenvalues and the corresponding normalized two-component wave functions are found by using the parametric generalization of the Nikiforov-Uvarov (NU) method. The numerical results show that the CLT interaction removes degeneracies between the spin and p-spin state doublets.     

Riemannian Geometry of Quantum Groups¶and Finite Groups with Nonuniversal Differentials

We construct noncommutative “Riemannian manifold” structures on dual quasitriangular Hopf algebras such as ℂ _q [SU ₂] with its standard bicovariant differential calculus, using the quantum frame bundle approach introduced previously. The metric is provided by the braided-Killing form on the braided-Lie algebra on the tangent space and the n-bein by the Maurer–Cartan form. We also apply the theory to finite sets and in particular to finite group function algebras ℂ[G] with differential calculi and Killing forms determined by a conjugacy class. The case of the permutation group ℂ[S ₃] is worked out in full detail and a unique torsion free and cotorsion free or “Levi–Civita” connection is obtained with noncommutative Ricci curvature essentially proportional to the metric (an Einstein space). We also construct Dirac operators in the metric background, including on finite groups such as S ₃. In the process we clarify the construction of connections from gauge fields with nonuniversal calculi on quantum principal bundles of tensor product form. Received: 22 June 2000 / Accepted: 26 August 2001     

Economy of effort in different speaking conditions. I. A preliminary study of intersubject differences and modeling issues

This study explores the hypothesis that clear speech is produced with greater "articulatory effort" than normal speech. Kinematic and acoustic data were gathered from seven subjects as they pronounced multiple repetitions of utterances in different speaking conditions, including normal, fast, clear, and slow. Data were analyzed within a framework based on a dynamical model of single-axis frictionless movements, in which peak movement speed is used as a relative measure of articulatory effort (Nelson, 1983). There were differences in peak movement speed, distance and duration among the conditions and among the speakers. Three speakers produced the "clear" condition utterances with movements that had larger distances and durations than those for "normal" utterances. Analyses of the data within a peak speed, distance, duration "performance space" indicated increased effort (reflected in greater peak speed) in the clear condition for the three speakers, in support of the hypothesis. The remaining four speakers used other combinations of parameters to produce the clear condition. The validity of the simple dynamical model for analyzing these complex movements was considered by examining several additional parameters. Some movement characteristics differed from those required for the model-based analysis, presumably because the articulators are complicated structurally and interact with one another mechanically. More refined tests of control strategies for different speaking styles will depend on future analyses of more complicated movements with more realistic models.     

Quasi-radial wall jets as a new concept in boundary layer flow control

This work aims to introduce a novel concept of wall jets wherein the flow is radially injected into a medium through a sector of a cylinder, called quasi-radial (QR) wall jets. The results revealed that fluid dynamics of the QR wall jet flow differs from that of conventional wall jets. Indeed, lateral and normal propagations of a conventional three-dimensional wall jet are via shear stresses. While, lateral propagation of a QR wall jet is due to mean lateral component of the velocity field. Moreover, discharged Arrays of conventional three-dimensional wall jets in quiescent air lead to formation of a combined wall jet at large distant from the nozzles, while QR wall jet immediately spread in lateral direction, meet each other and merge together very quickly in a short distance downstream of the jet nozzles. Furthermore, in discharging the conventional jets into an external flow, there is no strong interaction between them as they are moving parallel. While, in QR wall jets the lateral components of the velocity field strongly interact with boundary layer of the external flow and create strong helical vortices acting as vortex generators.     

Characterization of ion irradiated silicon surfaces ablated by laser-induced breakdown spectroscopy

Low energy metallic ions,generated by a Q-switched Nd:YAG laser(1064-nm wavelength,10-mJ energy,9-nm～12-ns-pulse width,10~(11)W/cm~2intensity)irradiated on a silicon substrate to modify various properties,such as electrical,morphological,and structural modifications.Thomson parabola technique is used to calculate the energy of these metallic ions whereas the electrical conductivity is calculated with the help of Four-point probe.Interestingly circular tracks forming chain like damage trails are produced via these energetic ions which are carefully examined by optical microscopy.It is observed that excitation,ionization,and cascade collisions are responsible for surface modifications of irradiated samples.Four-point probe analysis revealed that the electrical conductivity of substrate has reduced with increasing trend of atomic number of irradiated metallic ions(Al,Ti,Cu,and Au).The x-ray diffraction analysis elucidated the crystallographic changes leading to reduction of grain size of N-type silicon substrate,which is also associated with the metallic ions used.The decreasing trend of conductivity and grain size is due to thermal stresses,scattering effect,structural imperfections,and non-uniform conduction of energy absorbed by substrate atoms after the ion irradiation.     

Numerical study of magnetic nanoparticles concentration in biofluid (blood) under influence of high gradient magnetic field

Ferrofluids are widely used in pharmaceutical industries as magnetic separation tools, anti-cancer drug carriers and micro-valve applications. The purpose of the current study is to investigate the effect of a magnetic field on the volume concentration of magnetic nanoparticles of a non-Newtonian biofluid (blood) as a drug carrier. The effect of particles on the flow field is considered. The governing non-linear differential equations, concentration and Naviar-stokes are coupled with the magnetic field. To solve these equations, a finite volume based code is developed and utilized. The results show accumulation of magnetic nanoparticles near the magnetic source until it looks like a solid object. The accumulation of nanoparticles is due to the magnetic force that overcomes the fluid drag force. As the magnetic strength and size of the magnetic particles increase, the accumulation of nanoparticles increases, as well. The magnetic susceptibility of particles also affects the flow field and the contour of the concentration considerably.     

One-pot synthesis of 1,2,3-triazole linked dihydropyrimidinones via Huisgen 1,3-dipolar/Biginelli cycloaddition

The combination of the Biginelli reaction with click chemistry has been used for the one-pot synthesis of 1,2,3-triazole linked dihydropyrimidinones from azides, aromatic aldehydes containing a propargyl ether group, urea, and 1,3-dicarbonyl compounds using Cu(OAc)₂/sodium ascorbate as catalyst in acetic acid under mild reaction conditions.     

Laser based fabrication of chitosan mediated silver nanoparticles

We report fabrication of silver nanoparticles (Ag NPs) by laser ablation technique in different concentrations of aqueous chitosan solution. The ablation process of silver plate was carried out by using a nanosecond Q-switched Nd:YAG pulsed laser and the characterization of Ag NPs was done by Transmission electron microscopy, UV-Vis spectroscopy, and X-ray diffraction. UV-visible plasmon absorption spectra revealed that the formation efficiency as well as the stability of nanoparticles was increased by addition of chitosan. On the other hand, the size decrement of nanoparticles was more remarkable in the higher chitosan concentration.