Cooling of an electronic board situated in various configurations inside an enclosure: lattice Boltzmann method

Natural convection heat transfer in a square cavity induced by heated electronic board (as a thin plate at constant temperature) is investigated using the lattice Boltzmann method. Lattice Boltzmann simulation of natural convective heat transfer in a cavity in the presence of internal straight obstacle has not been considered completely in the literature and this challenge is generally considered to be an open research topic that may require more study. The present work is an extension to our previous paper (see Nazari and Ramzani in Modares. Mech. Eng. 11(2):119–133, 2011) in which the effects of position and dimensions of obstacle on the flow pattern and heat transfer rate are completely studied. A suitable forcing term is represented in the Boltzmann equation. With the representation, the Navier–Stokes equation can be derived from the lattice Boltzmann equation through the Chapman-Enskog expansion. Top and bottom of the cavity are adiabatic; the two vertical walls of the cavity have constant temperatures lower than the plate’s temperature. The study is performed for different values of Grashof number ranging from 10³ to 10⁵ for different aspect ratios and position of heated plate. The effect of the position and aspect ratio of heated plate on heat transfer are discussed and the position of the obstacle in which the maximum rate of heat transfer is investigated in both vertical and horizontal situation. The obtained results of the lattice Boltzmann method are validated with those presented in the literature.     

Realization of single and double axial InSb–GaSb heterostructure nanowires

Heteroepitaxial growth of III‐Sb nanowires allows for the formation of various interesting complex structures and enables the combination of their remarkable properties. In this Letter, we investigate the heteroepitaxial growth of Au‐seeded InSb and GaSb nanowires using metalorganic vapor phase epitaxy. We demonstrate successful single and double axial InSb–GaSb heterostructures in both directions. The formation properties of the grown nanowires including the compositional change of the particle and the interface sharpness are further discussed. In addition, the decomposition of InSb and GaSb segments and their side facet evolution are explained.

     

Molecular dynamics simulation for studying the stability of structure H clathrate-hydrates of argon and large guest molecules

The aim of present paper is to study the stability of (argon + large guest molecules) structure H clathrate-hydrates by using molecular dynamics simulations and with employing the COMPASS force field to consider the molecular interactions. The simulations are performed by embedding the structure H clathrate-hydrates in a simulation cell under isobaric-isothermal (NPT) conditions. The obtained equilibrium lattice parameters are compared with the experimental data, where a good consistency is observed. The results show that the size and dipole moment of the guest molecules enclosed in the hydrate cages play the main role in the interactions between the guest molecules and the water molecules, which constitute the surrounding walls of the hydrate cage and these interactions would stabilize the hydrate structure. The characteristics of the clathrate-hydrate structure are analyzed by evaluating the radial distribution function, where the agreement between the results obtained in this work and other similar theoretical and experimental investigations validates the simulation procedure and related interpretations.     

Optimization of Formulation and Process Variables for the Preparation of Novel Doxorubicin-Loaded Sonosensitive Nanodroplets

In the present study the effect of process (homogenization speed) and formulation (polymer concentration, surfactant concentration, drug amount, perfluorohexane volume fraction and co-surfactant inclusion) variables on particle size, entrapment efficiency, and drug release kinetics of doxorubicin-loaded alginate stabilized perfluorohexane nanodroplets were evaluated. Particle size and doxorubicin entrapment efficiency were highly affected by formulation and process variables. In vitro release profile of doxorubicin from all formulations was an apparently biphasic release process and 7–13 % of drug released from nanodroplets after 24 h incubation in PBS, pH 7.4, depending on the nanodroplets composition but ultrasound exposure for 10 min resulted in triggered release of 85.95 % of doxorubicin fromoptimal formulation (G). The inclusion of Span 60 (0.15 %), Poloxamer 188 (0.15 %) as co-surfactants reduced the particle size of nanodroplets from 51.8 to 42.3 and 35.6 nm, respectively. The entrapment efficiency decreased for span 60, while it did not changed in the case of Poloxamer 188. Comparison of drug release kinetics demonstrated that drug release was delayed for both Span 60 and Poloxamer 188. Thus, it was concluded that the particle size, entrapment efficiency and the doxorubicin release kinetics could easily be adjusted by taking advantage of process and formulation variables.     

Thiol-Capped Gold Nanoparticle Biosensors for Rapid and Sensitive Visual Colorimetric Detection of <Emphasis Type="Italic">Klebsiella pneumoniae</Emphasis>

In the last few years, gold nanoparticle biosensors have been developed for rapid, precise, easy and inexpensive with high specificity and sensitivity detection of human, plant and animal pathogens. Klebsiella pneumoniae serotype K2 is one of the common gram-negative pathogens with high prevalence. Therefore, it is essential to provide the effective and exclusive method to detect the bacteria. Klebsiella pneumoniae serotype K2 strain ATCC9997 genomic DNA was applied to establish the detection protocol either with thiol-capped oligonucleotide probes and gold nanoparticles or polymerase chain reaction based on K2A gene sequence. In the presence of the genomic DNA and oligonucleotide probes, a change in the color of gold nanoparticles and maximum changes in wavelength at 550-650 nm was achieved. In addition, the result showed specificity of 15?×?10⁵ CFU/mL and 9 pg/μL by gold nanoparticles probes. The lower limit of detection obtained by PCR method was 1 pg/μL. Moreover, results demonstrated a great specificity of the designed primers and probes for colorimetric detection assay and PCR. Colorimetric detection using gold nanoparticle probe with advantages such as the lower time required for detection and no need for expensive detection instrumentation compared to the biochemical and molecular methods could be introduced for rapid, accurate detection of the bacteria.     

Nanoparticle using parallel split rings and implementation of chain for creating Fano resonance with polarization independence for energy harvesting in mid-infrared

In optical devices, the polarization of the incident wave affects the Nano particle characteristics. Therefore, designing a polarization-independent device is significant in the process of designing optical structures. On the other hand, the concept of Fano resonance and dark mode has been utilized for achieving more energy enhancement. In this paper, we have developed a symmetrical Nano antenna by employing Fano resonance, which is independent of the incident wave polarization. The proposed Nano antenna is modified in mid infrared regime for biosensing and energy harvesting applications. The designed metamaterial antenna is made by Nano split ring resonators with etched capacitive gaps, which are utilized for concentrating energy. The introduced Nano antenna has a bright and dark mode with a weak enhancement of electric field. The effect of the incident wave polarization is investigated at wave incident angles between 0° and 45° to illustrate the independency of the polarization due to the symmetrical shape of the Nano antenna. In order to trigger the dark mode and enhance the electric field, a Nano chain is incorporated in the final structure. This arrangement has led to increasing of electric field drastically. Furthermore, the figure of merit has been calculated as an advantageous factor in sensing the surrounding materials with various refractive indices. Our findings illustrated that the chain arrangement has caused a peak in the linear form of the extinction cross section of the Nano antenna. This in turn has resulted in the appearance of Fano resonance with no impact on the resonance frequency that has been originally adjusted by capacitive gaps and inductive strips.     

Leading students towards the formal world of mathematical thinking: a mathematician’s reflections on teaching eigentheory

ABSTRACT

In this study, we analysed a mathematician’s teaching journals on eigenvalues and eigenvectors in a first-year linear algebra course. The research team employed Tall’s [How humans learn to think mathematically: Exploring the three worlds of mathematics. Cambridge University Press] three-world model of embodied, symbolic and formal as a framework for understanding the mathematician and teacher’s pedagogical reflections as he led the class to the formal world. In order to reach the formal world, he used a sequence of tasks that emphasized embodied and symbolic, as well as formal thinking. The analysis of the journals showed that the mathematician faced challenges in leading the class towards the formal world. The study also revealed that the mathematician strived to build a concept image, that, while perhaps mirroring his own, did not resonate with the students.     

Sodium Butylated Hydroxytoluene (NaBHT) as a New and Efficient Hydride Source for Pd-Catalysed Reduction Reactions

NaBHT (sodium butylated hydroxytoluene), a hindered and soluble base for the efficient arylation of various base-sensitive amines and (hetero)aryl halides has been found to have an unanticipated role as a hydride donor to reduce (hetero)aryl halides and allylic acetates. Mechanistic studies have uncovered that NaBHT, but not BHT, can deliver multiple hydrides through oxidation of the benzylic methyl group in NaBHT to the aldehyde. Further, performing the reduction with NaBHT-d₂₀ has revealed that the redox-active benzylic position is not the only hydride donor site from NaBHT with one hydride in three coming, presumably, from the tert-butyl groups. The reduction works well under mild conditions and, incredibly, only consumes 20 percent of the NaBHT in the process; the remaining 80 percent can be readily recovered in pure form and reused. This, combined with the low cost of the material in ton-scale quantity, makes it practical and attractive for wider use in industry at scale.     

Evaluation of the reaction mechanism for photocatalytic degradation of organic pollutants with MIL-88A/BiOI structure under visible light irradiation

Research on Chemical Intermediates - In this study, we synthesized novel visible light photocatalyst MIL-88A/BiOI using depositing BiOI particles on the surface of a metal–organic framework...