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Number of results: 7
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Abstract

Superparamagnetic iron oxide nanoparticles (SPION) synthesised chemically usually need the modification of the particle surface. Other natural sources of magnetic particles are various magnetotactic bacteria. Magnetosomes isolated from magnetotactic bacteria are organelles consisting of magnetite (Fe3O4) or greigite (Fe3S4) crystals enclosed by a biological membrane. Magnetotactic bacteria produce their magnetic particles in chains. The process of isolation of magnetosome chains from the body of bacteria consists of a series of cycles of centrifugation and magnetic decantation. Using a high-energy ultrasound it is possible to break the magnetosome chains into individual nanoparticles – magnetosomes. This study presents the effect of sonication of magnetosome suspension on their acoustic properties, that is speed and attenuation of the sound. Acoustic propagation parameters are measured using ultrasonic spectroscopy based on FFT spectral analysis of the received pulses. The speed and attenuation of ultrasonic waves in magnetosome suspensions are analysed as a function of frequency, temperature, magnetic field intensity, and the angle between the direction of the wave and the direction of the field.
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Authors and Affiliations

Arkadiusz Józefczak
Tomasz Hornowski
Anita Król
Matúš Molčan
Błażej Leszczyński
Milan Timko
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Abstract

Main aim of this study is to combine the characteristics of the sonic crystal (SC) with acoustic panels and porous materials to improve the sound transmission loss (STL) through the triple-panel structure. SCs cause a bandgap centered around a certain frequency (Bragg’s frequency) due to generation of destructive interference. Initially, an analytical method is developed that extends the previous theory of double-panel structure to predict STL through a triple-panel structure. Finite element (FE) simulations are performed to obtain the STL through the triple-panel, which are validated with the analytical predictions. Various configurations are analyzed using the FE method based on the method of inserting the porous material and SCs between the panels to address the combined effect. STL through the triple-panel structure is compared with that through the double-panel structure having the same total weight and total thickness. It is found that the combined structure of the triple panel and the SC with glass wool as filler gives the best soundproof performance for the same external dimensions. For narrow air gaps, filing with glass wool is more advantageous than inserting one row of SC. In addition, the triple panel combined with a SC has better soundproofing than the two-panel counterparts.

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Authors and Affiliations

Myong-Jin Kim
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Abstract

Sound insulation of the finite double-panel structure (DPS) inserted with a cylindrical shell array is investigated by varying the sound incidence direction to improve its applicability. The effects of the vibro-acoustic characteristics of its constituents on the sound transmission loss (STL) are estimated in one-third octave bands from 20 Hz to 5 kHz for different incidence conditions. It shows that the first acoustic mode in the direction parallel to two panels (longitudinal modes) produces both the sudden variation of sound insulation with frequency and a large dependency on the incidence angle. Mineral wools are placed on two boundaries perpendicular to the panels, and the sound insulation is explored for different thicknesses of the porous materials. An absorbent layer with a certain thickness (more than 30 mm in our work) sufficiently eliminates the longitudinal mode, resulting in the improvement in the sound insulation by more than 15 dB and the decrease of its large variation with incidence direction. STLs with varying shell thicknesses are also assessed. It shows that the natural vibrations of the thin shells can give an enhancement in sound insulation by more than 10 dB in the frequency range of 1600–3700 Hz, corresponding to constructive interference.
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Authors and Affiliations

Song-Hun Kim
1
Myong-Jin Kim
1

  1. Institute of Acoustics, Department of Physics, Kim Il Sung University, Pyongyang, Democratic People’s Republic of Korea
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Abstract

In this paper, we present one approach to improve the soundproofing performance of the double-panel structure (DPS) in the entire audible frequencies, in which two kinds of local resonances, the breathing-type resonance and the Helmholtz resonance, are combined. The thin ring resonator row and slit-type resonator (Helmholtz resonator) row are inserted between two panels of DPS together. Overlapping of the band gaps due to the individual resonances gives a wide and high band gap of sound transmission in the low frequency range. At the same time, the Bragg-type band gap is created by the structural periodicity of the scatterers in the high audible frequency range. In addition, the number of scatterer rows and the filling factor are investigated with regard to the sound insulation of DPS with sonic crystals (SCs). Consequently, the hybrid SC has the potential of increasing the soundproofing performance of DPS in the audible frequency range above 1 kHz by about 15 dB on average compared to DPS filled only with glass wool between two panels, while decreasing the total thickness and mass compared to the counterparts with the other type of local resonant sonic crystal.
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Authors and Affiliations

Kyong-Su Ri
1
Myong-Jin Kim
1
Se-Hyon Son-U
1

  1. Institute of Acoustics, Department of Physics, Kim Il Sung University, Pyongyang, Democratic People’s Republic of Korea
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Abstract

Liquid Phase Exfoliation (LPE) is a common route to produce two-dimensional MoS2 nanosheets. In this research, MoS2 powder is exfoliated by an ultrasonic probe (sonicator) in a water-ethanol solution. It is reported that MoS2 as a prototype 2D Transition Metal Dichalcogenide, has a band gap that increases with a decreasing number of layers. There are some factors that affect the average band gap energy value and the thickness of the exfoliated flakes. We varied different parameters of the ultrasonic probe like power, pulse percentage and time duration of sonication to investigate the effects on the number of MoS2 layers. Our findings from the UV-Visible spectra, SEM, FESEM and TEM images indicate that the minimum thickness for these samples was acquired at 50% of the input power of the sonicator we used (65 W) and the optimum pulse percentage is 50%. The current study also found that the average amount of band gap increased with an increase in sonication time, and then remained unchanged after 60 minutes.
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Authors and Affiliations

Najme Sadat Taghavi
1
Reza Afzalzadeh
1

  1. Faculty of Physics K.N. Toosi University of Technology Tehran 15418-49611, Iran
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Abstract

An approach is presented to form and broaden the low-frequency band gap of the double panel structure (DPS) by using a locally resonant sonic crystal (LRSC) in this work. The LRSC is made of cylindrical Helmholtz resonators arranged on square lattice. Their designs are similar to a slot-type resonator, but have different depths of slot. Elongating the slit neck inward and distributing the depths of slots produce a broad local resonant band gap at low frequencies: an average insertion loss (IL) of 10.9 dB covering 520 Hz to 1160 Hz with a LRSC of 12 cm width. Next, the effect of porous material filled into the resonators on the local resonant band gap is evaluated. It is shown that filling of porous material into the resonators decreases the height and width of the local resonant band gap. Finally, the transmission losses (TLs) through the DPS with LRSC are calculated as a function of the incident angle of the sound wave for LRSC embedded in porous material and not. The results show that the porous material can be significantly reduce the incident angle dependency of TL through the DPS with LRSC.
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Authors and Affiliations

Myong-Jin Kim
1
Chun-Gil Rim
1
Kyong-Su Won
1

  1. Institute of Acoustics, Department of Physics, Kim Il Sung University, Pyongyang, Democratic People’s Republic of Korea
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Abstract

Tannic acid or tannin, type of phenolic compound contains in kenaf bast fibre. Conventional extraction has certain limitations in terms of time, energy, and solvent consumption. Ultrasound assisted extraction (UAE) can extract bioactive components in shorter time, low temperature, with lesser energy and solvent requirement. UAE as alternative extraction technique is better equipped to retain the functionality of the bioactive compounds. In this study, the conditions for ultrasound assisted extraction (UAE) of tannic acid from kenaf bast fibre by assessing the effect of sonication time and different duty cycles were optimized. The use of ultrasound to extract tannic acid from kenaf bast fiber was evaluated. Ultrasound-assisted extraction (UAE) was carried out using ethanol as solvent to intensify the extraction efficacy. Phytochemical screening was conducted to identify the presence of tannic acid in extracts. The extracts then were analyzed using High-Performance Liquid Chromatography (HPLC) and Scanning Electron Microscopy (SEM). It was found that 0.2429 mg/mL of tannic acid was obtained under the extraction conditions of extraction temperature of 40℃, sonication time of 20 minutes and duty cycle of 50%. From SEM analysis, it was found that the raw sample demonstrated rough surface and no porous but kenaf bast fibre display smoother surface with less impurities and few pores appeared after the extraction process using UAE. These results indicate that ultrasound-assisted extraction is an efficient method for extracting tannic acid from kenaf bast fibre with the advantages of lower extraction time and higher extraction yield.
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Authors and Affiliations

M. Mohamad
1
ORCID: ORCID
H.A. Ibrahim
1
M.F.M. Nasir
2
N.A. Mohidem
3
ORCID: ORCID
N.F. Shoparwe
1
P.T. Teo
1
ORCID: ORCID
M.N. Masri
1
ORCID: ORCID
A.R. Irfan
4 5
ORCID: ORCID

  1. Universiti Malaysia Kelantan, Faculty of Bioengineering and Technology, Jeli Campus, Kelantan, Malaysia
  2. National Kenaf and Tobacco Board, Kubang Kerian, Kelantan, Malaysia
  3. Universiti Putra Malaysia, Faculty of Engineering Selangor, Department of Biological and Agricultural Engineering, Malaysia
  4. Universiti Malaysia Perlis, Faculty of Mechanical Engineering Technology, Perlis, Malaysia
  5. Universiti Malaysia Perlis, Center of Excellence Geopolymer and Green Technology (CEGeoGTech), Perlis, Malaysia

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