Molecular dynamics simulations of acoustic absorption by a carbon nanotube

Acoustic absorption by a carbon nanotube (CNT) was studied using molecular dynamics (MD) simulations in a molecular domain containing a monatomic gas driven by a time-varying periodic force to simulate acoustic wave propagation. Attenuation of the sound wave and the characteristics of the sound field due to interactions with the CNT were studied by evaluating the behavior of various acoustic parameters and comparing the behavior with that of the domain without the CNT present. A standing-wave model was developed for the CNT-containing system to predict sound attenuation by the CNT and the results were verifi ed against estimates of attenuation using the thermodynamic concept of exergy. This study demonstrates acoustic absorption effects of a CNT in a thermostatted MD simulation, quanti es the acoustic losses induced by the CNT and illustrates their effects on the CNT. Overall, a platform was developed for MD simulations that can model acoustic damping induced by nanostructured materials such as CNTs, which can be used to further understanding of nanoscale acoustic loss mechanisms associated with molecular interactions between acoustic waves and nanomaterials.M. Ayub, A. C. Zander, D. M. Huang, C. Q. Howard and B. S. Cazzolat

Molecular dynamics simulation of classical sound absorption in a monatomic gas

Sound wave propagation in argon gas is simulated usingmolecular dynamics (MD) in order to determine the attenuation of acoustic energy due to classical (viscous and thermal) losses at high frequencies. In addition, amethod is described to estimate attenuation of acoustic energy using the thermodynamic concept of exergy. The results are compared against standing wave theory and the predictions of the theory of continuum mechanics. Acoustic energy losses are studied by evaluating various attenuation parameters and by comparing the changes in behavior at three different frequencies. This study demonstrates acoustic absorption effects in a gas simulated in a thermostatted molecular simulation and quantifies the classical losses in terms of the sound attenuation constant. The approach can be extended to further understanding of acoustic loss mechanisms in the presence of nanoscale porous materials in the simulation domain.M. Ayub, A.C. Zander, D.M. Huang, B.S. Cazzolato, C.Q. Howar

Graphene oxide-based lamella network for enhanced sound absorption

Published online October 23, 2017Noise is an environmental pollutant with recognized impacts on the psychological and physiological health of humans. Many porous materials are often limited by low sound absorption over a broad frequency range, delicacy, excessive weight and thickness, poor moisture insulation, high temperature instability, and lack of readiness for high volume commercialization. Herein, an efficient and robust lamella-structure is reported as an acoustic absorber based on self-assembled interconnected graphene oxide (GO) sheets supported by a grill-shaped melamine skeleton. The fabricated lamella structure exhibits ≈60.3% enhancement over a broad absorption band between 128 and 4000 Hz (≈100% at lower frequencies) compared to the melamine foam. The enhanced acoustic absorption is identified to be structure dependent regardless of the density. The sound dissipation in the open-celled structure is due to the viscous and thermal losses, whereas it is predominantly tortuosity in wave propagation and enhanced surface area for the GO-based lamella. In addition to the enhanced acoustic absorption and mechanical robustness, the lamella provides superior structural functionality over many conventional sound absorbers including, moisture/mist insulation and fire retardancy. The fabrication of this new sound absorber is inexpensive, scalable and can be adapted for extensive applications in commercial, residential, and industrial building structures.Md Julker Nine, Md Ayub, Anthony C. Zander, Diana N. H. Tran, Benjamin S. Cazzolato and Dusan Losi

Fluorometric quantification of protoporphyrin IX in biological skin samples from in vitro penetration/permeation studies

A fluorometric analytical method was developed for quantification of protoporphyrin IX (PpIX) in skin samples and receptor phase solution after in vitro cutaneous penetration/permeation studies. Analytical conditions used were: excitation and emission wavelengths: 400 nm and 632 nm; bandwidth: 0.5 nm; excitation and emission slits: 10/10. PpIX was recovered from two different layers of skin, the stratum corneum (SC) and the epidermis plus dermis ([E+D]), by vortex homogenization, probe and bath sonication, using DMSO as an extraction solvent. The detection and quantification limits were 0.002 and 0.005 &#956;g/mL, respectively. The assay was linear from 0.005 - 0.5 &#956;g/mL. The within-day and between-day assay precision and accuracy in DMSO and receptor phase solution were each studied at the two concentration levels 0.04 and 0.2 &#956;g/mL, and 0.01 and 0.08 &#956;g/mL, respectively. The coefficients of variation and deviation from the theoretical values were lower than 5%. The skin recovery of PpIX from SC and [E+D] layers using two different concentrations (0.5 and 1.0 &#956;g/mL) were all above 90.0%. The method described has potential application to in vitro penetration/permeation studies of PpIX using porcine skin as a biological membrane model.<br>Um método analítico por espectrofluorimetria foi desenvolvido para quantificar a protoporfirina IX (Pp IX) em amostras de pele e fase receptora após a realização de testes in vitro de penetração/permeação cutâneas. As condições analíticas utilizadas foram: comprimentos de onda de excitação e emissão: 400 nm e 632 nm; largura de banda: 0,5 nm; fendas de excitação e emissão: 10/10. A PpIX foi extraída de amostras de estrato córneo (EC) e da epiderme sem estrato córneo + derme ([E+D]) através da agitação em vórtex e sonicação por haste e banho, utilizando-se o DMSO como solvente extrator. O limite de detecção e quantificação foram, respectivamente, de 0,002 e 0,005 &#956;g/mL. O método mostrou-se linear da faixa de 0,005 - 0,5 &#956;g/mL. A precisão e exatidão intra e inter-ensaio em DMSO e na fase receptora foram validadas utilizando-se duas concentrações distintas, respectivamente, de 0,004 e 0,2 &#956;g/mL, e 0,01 e 0,08 &#956;g/mL. Os valores de coeficiente de variação e o desvio do valor teórico foram inferiores a 5%. A recuperação da PpIX das camadas da pele (EC e [E+D]) utilizando-se duas concentrações distintas (0,5 e 1,0 &#956;g/mL) foram todas acima de 90,0%. O método descrito pode ser utilizado para determinação da PpIX após estudos de penetração/permeação cutânea in vitro utilizando pele de porco como modelo de membrana

Biochemical characterisation of a glucoamylase from Aspergillus niger produced by solid-state fermentation

In this work, glucoamylase was produced by Aspergillus niger in solid-state fermentation. The enzyme was partially purified by ammonium sulphate precipitation and ion exchange and gel filtration chromatographies. Its molecular mass was estimated as 118.17 kDa by electrophoresis. The partially purified enzyme had an optimum pH range of 4.5-5.0 and an optimum temperature of 60 °C, with average activity 152.85 U mL-1. Thermal and pH stability assays with the crude extract showed that more than 60 % of the activity remained at pH 4.6 and 60 °C, even after an exposition to these conditions longer than 24 h. Yet, after purification, the enzyme was stable at these for at least 4 h, which indicated that its purification for use in starch saccharification was inadvisable. K M and Vmax were 0.34 mg mL-1 and 160.22 U mL-1, respectively