Optimization of concentric array resonators for wide band noise reduction

In air duct noise control, Helmholtz resonators (HR) are considered as narrow band attenuators. For some applications they can be combined in line to form a wide band silencer. This study investigates the role of distance between HR side branch openings on the whole array attenuation. In the case of two resonators with same performance, the optimal distance can be calculated and corresponds to the quarter wave of HR mean frequency. On three or more HR arrays, relationships between resonators parameters and optimal lengths are much more complex. Tuning of such a device requires taking many geometrically coupled parameters into account; hence, design has to be automated. To operate this process, a 2D FEM COMSOL model has been coupled to a global MATLAB optimization solver. Among different types of constructions, arrays made of concentric resonators with transversal openings offers the most efficient and flexible design to optimize distance between openings. This methodology was applied to an existing turbo compressor silencer. Modifying openings and chambers arrangement, using the proposed approach increased the attenuation band by 10%. Another application concerning an air box for a two stroke engine was also investigated. This resulted in a 16L two chambers concept, being replaced by a more compact and more efficient, 8.3L wide band silencer, made of 8 resonators. With this approach it therefore becomes possible to handle available space and required noise attenuation on a required frequency band, all in one process.     

A Green Route for Synthesis of New 1,2-Naphthoquinomethane Acetonitriles in Water

A series of new 2-(3-hydroxy-4-oxo-4H-naphthalen-1-ylidene) acetonitriles was prepared by the cascade Michael addition-elimination reaction of sodium 1,2-naphthoquinone-4-sulfonate with various substituted acetonitriles compounds in ethanol-water in presence of basic catalyst.     

Exploring electronic versus steric effects in stereoselective ring-opening polymerization of lactide and β-butyrolactone with amino-alkoxy-bis(phenolate)-yttrium complexes

A series of methoxy‐amino‐bis(phenol)s (ONOO)H₂ possessing on the phenol rings R¹ ortho substituents with variable steric and electronic properties (R¹=CMe₂Ph, 1 ; CMe₂tBu, 3 ; CMe₂(4‐CF₃C₆H₄), 5 ; CPh₃, 9 ; Cl, 10 ) has been synthesized and further reacted with [Y{N(SiHMe₂)₂}₃](THF)₂ to give cleanly the corresponding yttrium compounds [Y(ONOO){N(SiHMe₂)₂}(thf)_n] ( Y‐x ); the solid‐state structures of Y‐3 and Y‐10 have been determined. These amido complexes have been used as initiators for the ring‐opening polymerization (ROP) of rac‐lactide (LA) and rac‐β‐butyrolactone (BBL) to provide heterotactically enriched poly(lactic acid)s (PLAs) and syndiotactically enriched poly(3‐hydroxybutyrate)s (PHBs), respectively, by means of a chain‐end control mechanism. Most of these polymerizations proceeded in a controlled fashion, giving polymers with narrow polydispersities and experimental molecular weights in good agreement with calculated values. The nature of the R¹ ortho substituents has a profound impact on the rates and, more spectacularly, on the stereocontrol of the polymerizations. The heterotactic stereocontrol in the ROP of rac‐LA appears to be governed essentially by steric considerations; the larger the substituent, the higher the heterotacticity: R¹=Cl (P_r=0.56)?CMe₃ (P_r=0.80)?CMe₂Ph (P_r=0.90)2(4 CF₃‐Ph) (P_r=0.93–0.94)≤CMe₂tBu (P_r=0.94–0.95)≤CPh₃ (P_r=0.95–0.96). On the other hand, the syndiotactic stereocontrol in the polymerization of rac‐BBL follows a quite different trend: R¹=Cl (P_r=0.42–0.45)?CMe₂tBu (P_r=0.62–0.70)3 (P_r=0.80)≤CMe₂(4 CF₃? Ph) (P_r=0.82–0.84)2Ph (P_r=0.89)3 (P_r=0.94), which suggests the involvement of electronic interactions. DFT computations on model intermediates confirmed a stabilizing C? H ??? π interaction between a methylene C? H of the ring‐opened BBL unit and the π system of one of the ortho‐aryl substituents of the ONOO ligand; by contrast, for model intermediates in the ROP of LA, no such C? H ??? π interaction involving the methyl group of lactate was observed.     

Removal of Reactive Yellow 84 from aqueous solutions by adsorption onto hydroxyapatite

The adsorption of a reactive dye, Reactive Yellow 84, from aqueous solution onto synthesized hydroxyapatite was investigated. The experiments were carried out to investigate the factors that influence the dye uptake by the adsorbent, such as the contact time under agitation, absorbent dosage, initial dye concentration, temperature and pH of dye solution. The experimental results show that the amount of dye adsorbed increases with an increase in the amount of hydroxyapatite. The maximum adsorption occurred at the pH value of 5. The equilibrium uptake was increased with an increase in the initial dye concentration in solution. The experimental isotherm data were analyzed using Langmuir isotherm equation. The maximum monolayer adsorption capacity was 50.25 mg/g. The adsorption has a low temperature dependency and was endothermic in nature with an enthalpy of adsorption of 2.17 kJ mol⁻¹.     

Effect of secondary polymer on self‐precipitation of pH‐sensitive polymethylmethacrylate derivatives Eudragit E100 and Eudragit L100

Interpolyelectrolyte complexes or polyplexes can be seen as interesting alternatives in the purpose of active ingredients encapsulation. Working on polymethylmethacrylate derivatives with special focus on controlled oral drug delivery, the influence of charged polyelectrolytes (polyacrylic acid, polyethylenimine, and amino‐dextran) and noncharged ones (polyvinyl alcohol, dextran 40, and Pluronic F68) has been investigated on the precipitation of two pH‐sensitive Eudragit polymers, namely, L100 and E100. Moreover, the possibility of preparing polyplexes involving the two polymethylmethacrylate derivatives with different charged and noncharged secondary polyelectrolytes has been studied. The obtained dispersions have been characterized in terms of mean particle size, size distribution, zeta potential, and morphology. Direct precipitation of Eudragit L100 by medium acidification in a batch process and in the presence of polyethylenimine allowed the production of particles with a narrow size distribution. The mean size was around 200 nm. In this case, the zeta potential was found to be +45 mV at pH = 7 in 1mM aqueous NaCl solution, and the produced suspension was stable in time since no aggregation and sedimentation have been observed. A precipitation pH of 8.16 allows us to suggest the preparation of a polyplex based on Eudragit L100 and polyethylenimine. In contrary, polyvinyl alcohol has shown ability to induce an increase in particle mean size whereas other polyelectrolytes showed no significant effect. Moreover, it was observed that polyethylenimine and polyacrylic acid solutions were able to directly induce Eudragit E100 precipitation whereas amino‐dextran and noncharged polyelectrolytes showed no effect on its precipitation and on particle size distribution.     

An Electrogenerated Base-Promoted Synthesis of 2-Aryl-3,3-Bis((Perfluoroalkyl) Thio)Acrylonitriles

Abstract

The preparation of 2-aryl-3,3-bis((perfluoroalkyl)thio)acrylonitriles is described. The electrogenerated cyanomethyl base/anion obtained from electroreduction of acetonitrile promotes reactions between arylacetonitrile, carbon disulfide, and perfluoroalkyl iodides. The new fluorinated acrylonitriles were obtained in good yields under mild reaction conditions.     

Use of a hybrid adaptive finite element/modal approach to assess the sound absorption of porous materials with meso-heterogeneities

The paper discusses the sound absorptive performance of a porous material with meso-perforations inserted in a rectangular waveguide using a numerical hybrid adaptive finite element-modal method. Two specific applications are investigated: (i) the improvement of porous materials noise reduction coefficient using meso-perforations (ii) the effects of lateral air gaps on the normal incidence sound absorption of mono-layer and two-layer porous materials. For the first application, a numerical design of experiments is used to optimize the sound performance of a porous material with meso-perforations with a reduced number of numerical simulation. An example in which the optimization process is carried out on the thickness and size of the perforation is presented to illustrate the relevance of the approach. For the second application, a set of twenty fibrous materials spanning a large flow resistivity range is used. Practical charts are proposed to evaluate the influence of air gaps on the average sound absorption performance of porous materials. This is helpful to both the experimenter regarding characterization of porous material based on Standing Wave Tube measurements and for the engineer to quantifying the impact of air gaps and for designing efficient absorbers.     

Sound transmission through a double panel structure periodically coupled with vibration insulators

In this paper, sound transmission through an aircraft sidewall representative double panel structure is investigated theoretically and parametric and validation studies are conducted. The studied configuration is composed of a trim panel (receiver side panel) attached to a ribbed skin panel (source side panel) with periodically spaced resilient mounts. The structure is considered infinite in order to use space harmonic expansion. The partition is also assumed planar for simplicity. The model allows for a 3D incident field and the panels can be metallic and/or composite. A four-pole formulation is employed for modeling of the mounts and the absorption provided by the fiberglass that fills the cavity between the leaves is addressed with an equivalent fluid model. The investigation of mount stiffness, damping and spacing show that properly designed mounts can increase the TL significantly (up to 20 dB of difference between rigid and resilient mounts). However, they can create undesirable resonances resulting from their interaction with the panels. The influence of cavity absorption is also studied and results illustrate the fact that it is not worth investing in a highly absorbent fiber if the structure-borne transmission path is not adequately insulated, and likewise that it is not worth investing in highly resilient mounts without sufficient cavity absorption. Moreover, the investigation of panel damping confirms that when structure-borne transmission is present, raising skin damping can increase the TL even below coincidence, but that on average, greater improvements are achieved by raising trim damping. Finally, comparison between the periodic model and finite element simulations for structure-borne transmission shows that the average level of transmitted energy is well reproduced with the periodic approach. However, the modes are only captured approximately due to the assumption of an infinite structure.     

Three novel oligosaccharides synthesized using Thermoanaerobacter brockii kojibiose phosphorylase

Background  

Recently synthesized novel oligosaccharides have been produced primarily by hydrolases and glycosyltransferases, while phosphorylases have also been subject of few studies. Indeed, phosphorylases are expected to give good results via their reversible reaction. The purpose of this study was to synthesis other novel oligosaccharides using kojibiose phosphorylase.