Fully developed mixed convection in horizontal and inclined tubes with uniform heat flux using nanofluid

Fully developed laminar mixed convection of a nanofluid consists of water and Al₂O₃ in horizontal and inclined tubes has been studied numerically. Three-dimensional elliptic governing equations have been solved to investigate the flow behaviors over a wide range of the Grashof and Reynolds numbers. Comparisons with previously published experimental and numerical works on mixed convection in a horizontal and inclined tube are performed and good agreements between the results are observed. Effects of nanoparticles concentration and tube inclinations on the hydrodynamics and thermal parameters are presented and discussed. It is shown that the nanoparticles concentration does not have significant effects on the hydrodynamics parameters. Heat transfer coefficient increases by 15% at 4 Vol.% Al₂O₃. Skin friction coefficient continually increases with the tube inclination, but the heat transfer coefficient reaches a maximum at the inclination angle of 45°.     

Two building blocks of microwave photonics filters in the presence of group delay ripple: a comparative survey

We have developed an analytic approach to investigate the effect of group delay ripple of the dispersive devices on the performance of two major building blocks of microwave-photonic filters. Firstly, performance of PM-based block in the presence of an arbitrary group delay ripple (GDR) is analyzed and compared with the ripple-free case to reveal the destructive effects of added group delay ripple. In the next step, we repeat the proposed approach for the AM-based one; again, the performance is compared with the ripple-free case. Two distortion metrics are also introduced to quantify this distortion. Comparison of the performance of two building blocks in the presence of group delay ripple unveils some interesting characteristics of microwave-photonic filters which have not been mentioned so far. We also add a general survey of two analyzed building blocks to present their respective most significant advantages and shortcomings. The simulated Optisystem results conform to our proposed analytical approach and verify the theoretical model.     

Highly edge-connected factors using given lists on degrees

Let G be a 2k-edge-connected graph with and let for every . A spanning subgraph F of G is called an L-factor, if for every . In this article, we show that if for every , then G has a k-edge-connected L-factor. We also show that if and for every , then G has a k-edge-connected L-factor.     

1-Methylimidazolium tetrafluoroborate [Hmim][BF4]: an efficient acidic ionic liquid catalyst for insertion of α-diazo compounds into the N–H bonds of amines

The reusable acidic ionic liquid, 1-methylimidazolium tetrafluoroborate [Hmim][BF₄], was found to be an effective catalyst for the insertion of α-diazoacetate into the N–H bonds of amines. The corresponding products were obtained in good yields and short reaction times via a simple procedure. The catalyst could be recycled and reused without any noticeable decrease in its activity.     

Crystal structure and DFT calculations of methanol {E-N′-(2-hydroxybenzlidene)benzohydrazido}dioxidomolybdenum (VI) complex

The crystal and molecular structure of methanol {E-N′-(2-hydroxybenzlidene)benzohydrazido}dioxidomolybdenum (VI) was determined by single crystal X-ray diffraction. B3LYP/DZP basis set theoretical calculations nicely reproduce the X-ray experimental geometry. The obtained results are discussed in connection with the electronic and structural properties of the compound.     

One-Pot Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones and Their Sulfur Derivatives with H2SO4 Supported on Silica Gel or Alumina

The one-pot condensation of aromatic aldehydes, β-dicarbonyl compounds, and urea or thiourea in the presence of H₂SO₄ supported on silica gel or alumina (80% m/m) in refluxing n-hexane produces 3,4-dihydropyrimidin-2(1H)-ones and their sulfur derivatives in high to excellent yields.     

The Efficient Synthesis of 3,4-Dihydropyrimidin-2-(1H)-Ones and Their Sulfur Derivatives with H2SO4 Immobilized on Activated Charcoal

Abstract

Various 3,4-dihydropyrimidin-2-(1H)-ones (DHPMs) and their sulfur derivatives were efficiently synthesized by a one-pot cyclocondensation reaction of aromatic and aliphatic aldehydes, β-dicarbonyl compounds and urea (or thiourea) in the presence of sulfuric acid immobilized on activated charcoal (133% w/w). The reactions were carried out in refluxing n-hexane-acetonitrile (2.5:0.5 mL) within 5–150 min to give 3,4-dihydropyrimidinones (or thiones) in high to excellent yields (81–97%).     

Synthesis of benzaldehyde-functionalized LewisX trisaccharide analogs for glyco-SAM formation

LewisX (Le^x) antigen based carbohydrate–carbohydrate interactions are mediated by complexation of metal ions. Although theoretical studies about the influence of participating hydroxyl groups in the Le^x trisaccharide head group (Galβ(1-4)[Fucα(1-3)]GlcNAc) could gave same rudimental information about the basic mechanism behind this interaction, a little is known about orientation and configuration of the hydroxyl groups required for the specific interaction mediated by Ca²⁺ complexation. Therefore, there is a need of non-natural derivatives to provide detailed information about the requirements for hydroxyl group arrangement in Le^x head group surface plasmon resonance and gold nanoparticle techniques have shown to be powerful tools to investigate carbohydrate–carbohydrate interactions. Benzaldehyde-functionalized glycans can be used for attachment to both gold nanoparticles and surface plasmon resonance sensor surfaces. Therefore, seven benzaldehyde equipped Le^x analogs including the natural trisaccharide were synthesized utilizing convergent approach. The derivatives were applied in ongoing carbohydrate–carbohydrate interaction studies by surface plasmon resonance experiments to prove theoretical postulate about the structural requirements of hydroxyl group arrangements in Le^x trisaccharides.     

Develop dissipative particle dynamics method to study the fluid flow and heat transfer of Ar and O2 flows in the micro- and nanochannels with precise atomic arrangement versus molecular dynamics approach

Fluid atomic behavior is an important factor for industrial applications. Computer simulations based on simple models predict Poiseuille flow for these atomic structures with the presence of external force. In this work, we describe the dynamical properties of Ar and O₂ flows with precise atomic arrangement via dissipative particle dynamics (DPD) and molecular dynamics (MD) simulation approaches. In these methods, each model is represented by using Large-scale Atomic/Molecular Massively Parallel Simulator package. Simulation results show that maximum rate for velocity of Ar flow in platinum and copper microchannels is 0.100 (unit less)/0.091 Å ps^?1 and 0.121 (unit less)/0.105 Å ps^?1 by using DPD/MD approach. This atomic parameter changes to 0.111 (unit less)/0.102 Å ps^?1 and 0.125 (unit less)/0.108 Å ps^?1 for O₂ fluid with mentioned approaches. By decreasing the microchannel size, the maximum rate of velocity reaches to 0.101 (unit less)/0.099 Å ps^?1 and maximum temperature rate decreases to 485 (unit less)/440 K with DPD/MD approaches. These calculated parameters can be used in industrial application designing for some processes such as heat transfer in structures. It was seen that the developed DPD approach was able to simulate the fluid flow and heat transfer of various types of fluids at micro- and nanoscales with suitable accuracy versus MD.