Effect of contraction on turbulent channel flow

Summary Measurements in an effectively two-dimensional channel indicate that flow acceleration at constant Reynolds Number can have appreciable effects on the turbulence structure. As in wakes, the structure approaches equilibrium exponentially after the acceleration. The effect of acceleration appears to be (at least qualitatively) of the same kind as is observed when turbulence is subjected to rapid distortion.

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Zusammenfassung Messungen in einem effektiv zwei-dimensionalen Kanal zeigen, daß eine Strömungsbeschleunigung bei konstanter Reynolds-Zahl einen wesentlichen Einfluß auf die Turbulenz-Struktur haben kann. Nach der Beschleunigung findet man eine exponentielle Annäherung an das Gleichgewicht, wie bei Dellen. Der Beschleunigungs-Effekt auf die Turbulenz erscheint, wenigstens qualitativ, von der gleichen Art zu sein wie der Einfluß von raschen Verformungen.

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Symbols c _f skin-friction coefficient = - D half-width of the channel - L length of contraction=12 inches - dp/dx pressure gradient - V mean velocity in thex-direction,U=U ₀ aty=D - U mean velocity - average of the mean velocity - U ^* friction velocity = (₀/)^± - root mean square value of the turbulent velocity fluctuations inx, y andz directions - X coordinate in the direction of the flow;X=0 at the end of contraction - Y coordinate perpendicular to the surface of the wall on which measurements are madey=0 at the wall andy=D at the centre of the channel - ₀ Wall shear stress - density of the fluid - viscosity of the fluid - kinematic viscosity of the fluid=/     

Some studies on transition from laminar to turbulent flow in a two-dimensional channel

Zusammenfassung In einem Wasserkanal wurden Versuche über den laminar-turbulenten Umschlag einer zweidimensionalen Strömung durchgeführt. Geschwindigkeitsmessungen der vorderen und hinteren Randzonen von künstlich erzeugten Turbulenz-Kernen ergaben eine (auf die mittlere Strömungsgeschwindigkeit und die Kanaltiefe bezogene) kritische Reynolds-Zahl von 1025±25. Messungen der Intermittenz längs des Kanals bei den Reynolds-Zahlen 3460, 3570 und 3850 zeigten, dass die Umschlagstheorie nach Emmons auch für Kanalströmung sinnvoll ist.     

Silica Sulfuric Acid as an Inexpensive and Recyclable Solid Acid Catalyzed Efficient Synthesis of Quinolines

Summary. Silica sulfuric acid as an inexpensive and recyclable solid acid efficiently catalyzes the Fridedl?nder synthesis of quinolines through a condensation reaction of a 2-aminoaryl ketone with an activated α-CH acid compound under solvent-free conditions in high yields at 100°C.     

One-Pot Green Synthesis of Hematite (α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>) Nanoparticles by Ultrasonic Irradiation and Their In Vitro Cytotoxicity on Human Keratinocytes CRL-2310

Greener and ecofriendly approaches to the synthesis of hematite (α-Fe₂O₃) nanoparticles are important for various biomedical applications. The authors describe on a facile, one-pot method for synthesizing hematite nanoparticles (HNPs) using ultrasonic irradiation of iron(III) oxide solution containing the aqueous root extract of Arisaema amurense, which was used as both reducing and stabilizing agents. The synthesized HNPs were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). FT-IR analysis indicated the presence of stabilizing groups such as hydroxyl (–OH), C–O, and amide (–NH–) on the surfaces of HNPs. TEM analysis revealed the formation of near spherical HNPs of average size 24.55 ± 6.9 nm. VSM confirmed the ferromagnetic nature of the HNPs with a saturation magnetization (Ms) at 1.25 emu/g and remanent magnetization (Mr) at 0.50 emu/g at 301 K. The electrochemical behavior of glassy carbon (GC)/HNPs electrode was studied using cyclic voltammetry (CV). MTT assays of the HNPs exhibited in vitro concentration-dependent cytotoxicity to human keratinocytes CRL-2310, which indicated the synthesized HNPs are compatible with requirements for in vivo biomedical applications at lower concentrations.     

The effect of silica nanoparticles on the stability of aqueous foams

An experimental study was performed on aqueous foams stabilized by a mixture of hexadecyltrimethylammonium bromide (HTAB) and negatively-charged silica nanoparticles. The effects of the nanoparticles on the stability of foams at different HTAB concentrations were investigated. The foams were characterized by measuring their foamability and stability. Rheological behavior of the foams was also studied. Furthermore, rheology of the air–water interfaces was studied in the linear and nonlinear deformation ranges. The thickness of the monolayer at the interface was measured. The actual size of the silica nanoparticles at the air–water interface was measured by transmission electron microscopy. Based on these measurements, the interaction between the monolayers across the foam film containing HTAB and nanoparticles was investigated. Smaller silica nanoparticles (i.e. diameter less than 10?nm) adsorbed at the air–water interface whereas the larger particles remained in the sub-phase or in the bulk liquid phase. It was found that these nanoparticles strongly influenced the foaming behavior at the low HTAB concentrations (i.e. below the CMC). A Langmuir-type monolayer was formed. The presence of the nanoparticles at the air–water interface provided mechanical strength to the foam films and prevented their rupture. This hindered coalescence of the bubbles, which resulted in a stable foam.     

Friedel-Crafts Acylation of Aryl-Substituted Carboxylic Acids Catalyzed by Zeolite

A convenient heterogeneous catalytic intramolecular Friedel-Craftsacylation of some aryl-substituted carboxylic acids overY-faujasite-type zeolite is described. It is an effective method forthe synthesis of 4,9-diketo-1,2,3,4-tetrahydroacenaphthenes.     

Topology-Matching Design of an Influenza-Neutralizing Spiky Nanoparticle-Based Inhibitor with a Dual Mode of Action

In this study, we demonstrate the concept of “topology-matching design” for virus inhibitors. With the current knowledge of influenza A virus (IAV), we designed a nanoparticle-based inhibitor (nano-inhibitor) that has a matched nanotopology to IAV virions and shows heteromultivalent inhibitory effects on hemagglutinin and neuraminidase. The synthesized nano-inhibitor can neutralize the viral particle extracellularly and block its attachment and entry to the host cells. The virus replication was significantly reduced by 6 orders of magnitude in the presence of the reverse designed nano-inhibitors. Even when used 24 hours after the infection, more than 99.999 % inhibition is still achieved, which indicates such a nano-inhibitor might be a potent antiviral for the treatment of influenza infection.     

Topology‐Matching Design of an Influenza‐Neutralizing Spiky Nanoparticle‐Based Inhibitor with a Dual Mode of Action

In this study, we demonstrate the concept of “topology‐matching design” for virus inhibitors. With the current knowledge of influenza A virus (IAV), we designed a nanoparticle‐based inhibitor (nano‐inhibitor) that has a matched nanotopology to IAV virions and shows heteromultivalent inhibitory effects on hemagglutinin and neuraminidase. The synthesized nano‐inhibitor can neutralize the viral particle extracellularly and block its attachment and entry to the host cells. The virus replication was significantly reduced by 6 orders of magnitude in the presence of the reverse designed nano‐inhibitors. Even when used 24 hours after the infection, more than 99.999 % inhibition is still achieved, which indicates such a nano‐inhibitor might be a potent antiviral for the treatment of influenza infection.