Steklov convexification and a trajectory method for global optimization of multivariate quartic polynomials

Mathematical Programming - The Steklov function $$mu _f(cdot ,t)$$ is defined to average a continuous function f at each point of its domain by using a window of size given by $$t>0$$ . It...     

Fabrication of magnetic gold nanorod particles for immunomagnetic separation and SERS application

The preparation and application of rod-shaped core–shell structured Fe₃O₄–Au nanoparticles for immunomagnetic separation and sensing were described for the first time with this study. To synthesize magnetic gold nanorod particles, the seed-mediated synthetic method was carried out and the resulting nanoparticles were characterized with transmission electron microscopy (TEM), ultraviolet visible spectroscopy (UV–Vis), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD). Magnetic properties of the nanoparticles were also examined. Characterization of the magnetic gold nanorod particles has proven that the resulting nanoparticles were composed of Fe₃O₄ core and the gold shell. The rod-shaped gold-coated iron nanoparticles have an average diameter of 16 ± 2 nm and an average length of about 50 ± 5 nm (corresponding aspect ratio of 3). The saturation magnetization value for the magnetic gold nanorod particles was found to be 37 emu/g at 300 K. Rapid and room temperature reaction synthesis of magnetic gold nanorod particles and subsequent surface modification with E. coli antibodies provide immunomagnetic separation and SERS application. The analytical performance of the SERS-based homogenous sandwich immunoassay system with respect to linear range, detection limit, and response time is also presented.     

Preconcentration and Determination of Manganese and Nickel from Various Water Samples by Nano Zirconium Oxide/Boron Oxide

ABSTRACT

This work assesses the potential of the adsorptive material nano zirconium oxide/boron oxide (ZrO₂/B₂O₃) for removal of trace Mn(II) and Ni(II) from environmental samples. This method is based on the sorption of Mn(II) and Ni(II) ions directly onto nanosorbent, followed by the elution and determination by flame atomic absorption spectrometry (FAAS). Experimental parameters, including pH of sample solution, volume and concentration of eluent, sample volume, and flow rate of sample solution, that affect the recovery of the Mn(II) and Ni(II) ions from model solutions have been optimized. Under the optimum conditions, adsorption isotherms and adsorption capacities have been examined. The recoveries of Mn(II) and Ni(II) were 96% ± 2% and 95% ± 3% at 95% confidence level, respectively. The analytical detection limits for Mn(II) and Ni(II) were 1.9 and 4.9 µ g L^?1, respectively. Adsorption capacities of the nano ZrO₂/B₂O₃ were found as 92.8 mg g^?1 for Mn and 168.4 mg g^?1 for Ni. The accuracy of the method was checked by analyzing certified reference material (SPS-WW1 wastewater) and spiked real samples. The method was applied for the determination of analytes in water samples.     

Non-convex rate dependent strain gradient crystal plasticity and deformation patterning

A rate dependent strain gradient crystal plasticity framework is presented where the displacement and the plastic slip fields are considered as primary variables. These coupled fields are determined on a global level by solving simultaneously the linear momentum balance and the slip evolution equation, which is derived in a thermodynamically consistent manner. The formulation is based on the 1D theory presented in Yalcinkaya et al. (2011), where the patterning of plastic slip is obtained in a system with non-convex energetic hardening through a phenomenological double-well plastic potential. In the current multi-dimensional multi-slip analysis the non-convexity enters the framework through a latent hardening potential presented in Ortiz and Repettto (1999) where the microstructure evolution is obtained explicitly via a lamination procedure. The current study aims the implicit evolution of deformation patterns due to the incorporated physically based non-convex potential.     

Transient temperature and thermally induced stress distributions in a partly-circumferentially heated cylindrical workpiece

This paper presents the numerical solutions of the transient temperature and thermally induced stress distributions in a partly-circumferentially heated cylindrical hollow workpiece (steel) with conjugate heat transfer. Outer surface of the workpiece is heated partly-circumferentially heat flux as its remainder outer surface is circumferentially cooled with fluid (water). Three phenomena have been considered as; (1) conduction inside the cylinder, (2) convection from the cylinder surface to the surrounding fluid, and (3) thermal stress produced by high temperature gradient inside the cylinder. The governing flow and energy equations have been solved numerically by using a control volume approach. The PHOENICS 3.2 and HEATING7 computer codes have been used for the numerical evaluation. The transient calculations have been performed individually for four fluid inlet velocities, u_i = 0.005, 0.01, 0.015 and 0.020 m/s, until the system attains steady-state. The results of this study clearly demonstrate that the temperature contours in the low inlet velocity cases are more near to a symmetric case with respect to the y = 0 plane than that in the high inlet velocity cases, and the increment of the inlet velocity exponentially reduces the temperatures and thermally induced stresses in the workpiece. The effective thermal stress differences occurring in the workpiece can be significantly reduced by the high fluid inlet velocity.     

Primes in tuples II

We prove that

$ \mathop{ \lim \inf}\limits_{n \rightarrow \infty} \frac{p_{n+1}-p_{n}}{\sqrt{\log p_{n}} \left(\log \log p_{n}\right)^{2}}< \infty, $

where p _n denotes the nth prime. Since on average p _n+1?p _n is asymptotically log _n , this shows that we can always find pairs of primes much closer together than the average. We actually prove a more general result concerning the set of values taken on by the differences p?p′ between primes which includes the small gap result above.

     

A critical analysis of N. Bohr's reply to the EPR argument

N. Bohr's counter-argument to EPR assumes that the complementarity principle imposes a limitation on the types of predictions permissible in quantum theory, similar to the limitation imposed on the types of measurements by the Heisenberg uncertainty relation. Since this assumption has no quantum-theoretical justification, the EPR argument cannot be refuted on the basis of the complementarity principle.     

Entropy generation in parallel plate microchannels

In this study the entropy generation in microchannels in microdevices induced by the transient laminar forced convection in the combined entrance region between two parallel plates has been investigated numerically. The study considers the microscales in the region of Kn < 0.001. The effects of aspect ratio, Reynolds number, Prandtl number, Brinkman number, and the motion of the lower plate on the entropy generation during the simultaneously developing flow in a parallel-plates channel are investigated. The obtained results addressing all cases are thoroughly in good agreement with the expectations that the entropy generation has its highest value at channel with the smallest aspect ratio at counter motion of the lower plate with the highest Re, Pr and Br/Ω values considered in the problem. An erratum to this article can be found at     

Comparison effects of different doping on spin-Peierls transition in CuGeO(3)

The comparison between non-magnetic spin-Peierls (SP) and magnetic Néel ground states have been investigated in CuGeO₃ doped with Zn²⁺, Ni²⁺ and Mn²⁺ ions by using the electron spin resonance (ESR) techniques in the temperature range of 3–300 K. It was concluded that the one-dimensional (1D) antiferromagnetic (AF) spin chain formed of spin-1/2 (Cu²⁺) ions is broken by spin-0 (Zn²⁺), spin-1 (Ni²⁺), and spin-5/2 (Mn²⁺) ions, giving uncoupled spins at the end of the chains that give extra contribution to the spectra at lower temperature. An almost linearly dependence of frequency of resonance field has been showed for X-, K- and Q-band spectra. By the analysis of resonance field–frequency relations, the effects of the internal field is refined and thus the spectroscopic g-factor and internal field were calculated to be g = 1.9386 and H_i = 148 G, respectively.