Hydrogen atom and its energy level shifts in de Sitter universe

We investigate the influence of a cosmological constant on the energy levels of a one-electron atom in Fermi normal coordinates. The non-relativistic nS, nP energy levels and the relativistic 1S _1/2, 2S _1/2, 2P _1/2, 2P _3/2 energy levels are calculated in terms of the Riemann tensor. These energy level shifts are non-zero which indicate that the first order gravitational perturbations can partly remove the degeneracy of the studied states in de Sitter space. We show that it is not possible to use the hydrogen atom as a probe of background curvature of the universe. In the second order of perturbation, for 1S state, an upper limit for the energy shifts is obtained.     

Nonlinear vibration of micromachined asymmetric resonators

In this paper, the nonlinear dynamics of a beam-type resonant structure due to stretching of the beam is addressed. The resonant beam is excited by attached electrostatic comb-drive actuators. This structure is modeled as a thin beam-lumped mass system, in which an initial axial force is exerted to the beam. This axial force may have different origins, e.g., residual stress due to micro-machining. The governing equations of motion are derived using the mode summation method, generalized orthogonality condition, and multiple scales method for both free and forced vibrations. The effects of the initial axial force, modal damping of the beam, the location, mass, and rotary inertia of the lumped mass on the free and forced vibration of the resonator are investigated. For the case of the forced vibration, the primary resonance of the first mode is investigated. It has been shown that there are certain combinations of the model parameters depicting a remarkable dynamic behavior, in which the second to first resonance frequencies ratio is close to three. These particular cases result in the internal resonance between the first and second modes. This phenomenon is investigated in detail.     

Nitrogen-doped carbon nanotubes for heat transfer applications

In this research, it is aimed to enhance the heat transfer properties of the carbon nanotubes through nitrogen doping. To this end, nitrogen-doped multiwall carbon nanotubes (N-CNTs) were synthesized via chemical vapor deposition method. For supplying carbon and nitrogen during the synthesis of N-CNTs, camphor and urea were used, respectively, at 1000 °C over Co–Mo/MgO nanocatalyst in a hydrogen atmosphere. N-CNTs with three different nitrogen loadings of 0.56, 0.98, and 1.38 mass% were synthesized, after which, water/N-CNT nanofluids of these three samples with concentrations of 0.1, 0.2, and 0.5 mass% were prepared. To obtain a stable nanofluid, N-CNTs were functionalized by nitric acid followed by stabilizing in water by employing the ultrasonic bath. Investigation on the stability of the samples showed a high stability level for the prepared water/N-CNT nanofluids in which the zeta potential of ??43.5 mV was obtained for the best sample. Also for studying the heat transfer properties, the thermal conductivity in the range of 0.1–0.5 mass% and convection heat transfer coefficients of nanofluids in the range of 0.1–0.5 mass%, and Reynolds number in the range of 4000–9000 were evaluated. The results showed 32.7% enhancement of the convection heat transfer coefficients at Reynolds number of 8676 and 27% increase in the thermal conductivity at 0.5 mass% and 30 °C.

     

Introducing the theory of successful settling in order to evaluate and optimize the sedimentation tanks

A rectangular settling tank in full scale is investigated using the Fluent software to increase its efficiency. First, the pure water is simulated in the absence of particles. Then particles are injected into the flow field and tracked by means of the discrete phase model. Three methods are presented to optimize the settling tank: (1) adding a baffle which is mounted in the bottom and is extended up to the near of free surface, (2) adding a baffle which is mounted in the free surface and is extended up to the near of the tank bottom and (3) install a bi-directional baffle which is mounted in the free surface and is extended up to the near of the bottom. These three suggestions are checked using the short-circuiting phenomenon and the successful settling theory. The successful settling theory states that a particle can be accounted as a “trapped” particle if (1) settled particle stays static and stable in the tank bottom and (2) settled particle doesn’t return to purified sewage. Although the second method provided higher efficiency, the third method was selected as the most appropriate method in order to optimize the settling tank.     

Isolation of PHA–Producing Bacteria from Date Syrup Waste

Since the major problem associated with the industrial production of Polyhydroxyalkanoates (PHAs) is their high production cost, this study was carried out using date syrup as the major carbon source to decrease the production cost and also help to supply other nutrient requirements. To isolate PHA–producing bacteria for this purpose, microorganisms were isolated from the syrup waste of a local date factory. These purified colonies were screened for intracellular granules by staining with Sudan Black. The positive-staining strains were grown for production of PHAs in 5% date syrup as carbon source supplemented with mineral salt medium. The culture was incubated at 30 °C with shaking at 140 rpm for 60 h. Among positively stained bacteria, the best PHA producers were selected on the basis of cell growth, cell dry weight, PHA content and the monomer composition of PHA. One of them could utilize date syrup for growth and produce the homopolymer of Polyhydroxybutyrate (PHB) with a cell density of about 5.1 g/L and maximum concentration of PHB equal to 3.6 g/L which is 71% of cell dry weight. Another one produces copolymer of Poly (hydroxybutyrate-hydroxyvalerate) in date syrup media with a maximum concentration of 2.2 g/L containing 10 wt % valerate in shake flask cultivation.     

Influence of acid catalysts on the structural and magnetic properties of nanocrystalline barium ferrite prepared by sol–gel method

BaFe₁₂O₁₉ powders with nanocrystalline size were prepared by sol–gel techniques. Nitric, hydrochloric, acetic and stearic acid were used to improve the magnetic properties. Amorphous gels were formed with Fe/Ba molar ratio of 10.5. Then powders were obtained by subsequent heat treatment at 800–1000 °C for 1 h. Barium ferrite powder was also synthesized by solid state reaction at 1210 °C. X-ray diffraction, scanning electron microscopy and transmission electron microscopy (TEM) experiments were conducted to evaluate structural properties of the samples. The value of the effective magnetic susceptibility was measured. The results show that the magnetoplumbite structure was formed in all of the powders. The TEM observation showed that the minimum particle size (20 nm) was produced with the stearic acid catalyst. The highest value of the effective magnetic susceptibility was achieved also using stearic acid.     

TiO2/Fe3O4/Multiwalled Carbon Nanotubes Nanocomposite as Sensing Platform for Simultaneous Determination of Morphine and Diclofenac at a Carbon Paste Electrode

Russian Journal of Electrochemistry - A nanocomposite of TiO2/Fe3O4/MWCNTs (TFMWCNT) and ionic liquid was used to fabrication of a novel modified carbon paste electrode. The modified electrode was...