scholarly journals Acoustic Attenuation Performance of Two-Pass Perforated Hybrid Mufflers with Mean Flow

2021 ◽  
Vol 26 (4) ◽  
pp. 306-315
Author(s):  
Yiliang Fan ◽  
Zhenlin Ji
Keyword(s):  
Analytical Approach ◽  
Transmission Loss ◽  
Glass Wool ◽  
Frequency Range ◽  
Mean Flow ◽  
Acoustic Attenuation ◽  
Fiber Glass ◽  
One Dimensional ◽  
The One ◽  
The Right

The one-dimensional (1-D) analytical approach is developed to predict and analyze the acoustic attenuation performance of two-pass perforated hybrid mufflers in the presence of mean flow. The expressions of complex acoustic wavenumber and impedance of long fiber glass wool are presented by using the impedance tube measurement and curve fitting. The 1-D approaches as well as the fitting expressions are validated by comparing the predicted and measured transmission loss of two-pass perforated hybrid mufflers with a different Mach number. Results illustrate that the 1-D predictions agree well with measurements below the plane wave cut-off frequency and deviate in higher frequency range. The influences of geometric parameters including the lengths of extended tubes, perforations on the right bulkhead and the outlet tube, and mean flow on the acoustic attenuation behavior of the hybrid mufflers are examined.

ACOUSTIC ATTENUATION CHARACTERISTICS OF STRAIGHT-THROUGH PERFORATED TUBE SILENCERS AND RESONATORS

2008 ◽  
Vol 16 (03) ◽  
pp. 361-379 ◽  
Author(s):  
Z. L. JI
Keyword(s):  
Performance Prediction ◽  
Transmission Loss ◽  
Three Dimensional ◽  
Geometrical Parameters ◽  
Mean Flow ◽  
Acoustic Attenuation ◽  
One Dimensional ◽  
The One ◽  
Attenuation Characteristics ◽  
Perforated Tube

The one-dimensional analytical solutions are derived and three-dimensional substructure boundary element approaches are developed to predict and analyze the acoustic attenuation characteristics of straight-through perforated tube silencers and folded resonators without mean flow, as well as to examine the effect of nonplanar waves in the silencers and resonators on the acoustic attenuation performance. Comparisons of transmission loss predictions with the experimental results for prototype straight-through perforated tube silencers demonstrated that the three-dimensional approach is needed for accurate acoustic attenuation performance prediction at higher frequencies, while the simple one-dimensional theory is sufficient at lower frequencies. The BEM is then used to investigate the effects of geometrical parameters on the acoustic attenuation characteristics of straight-through perforated tube silencers and folded resonators in detail.

Effect of leakage and blockage on the acoustic behavior of particle filters

2019 ◽  
Vol 67 (6) ◽  
pp. 483-492
Author(s):  
Seonghyeon Baek ◽  
Iljae Lee
Keyword(s):  
Transfer Matrix ◽  
Particle Filters ◽  
Acoustic Analysis ◽  
Transmission Loss ◽  
One Dimensional ◽  
Filter System ◽  
The Difference ◽  
The One ◽  
Analytical Approaches ◽  
Good Agreement

The effects of leakage and blockage on the acoustic performance of particle filters have been examined by using one-dimensional acoustic analysis and experimental methods. First, the transfer matrix of a filter system connected to inlet and outlet pipes with conical sections is measured using a two-load method. Then, the transfer matrix of a particle filter only is extracted from the experiments by applying inverse matrices of the conical sections. In the analytical approaches, the one-dimensional acoustic model for the leakage between the filter and the housing is developed. The predicted transmission loss shows a good agreement with the experimental results. Compared to the baseline, the leakage between the filter and housing increases transmission loss at a certain frequency and its harmonics. In addition, the transmission loss for the system with a partially blocked filter is measured. The blockage of the filter also increases the transmission loss at higher frequencies. For the simplicity of experiments to identify the leakage and blockage, the reflection coefficients at the inlet of the filter system have been measured using two different downstream conditions: open pipe and highly absorptive terminations. The experiments show that with highly absorptive terminations, it is easier to see the difference between the baseline and the defects.

Effect of Double Defects on Transmission Spectra of One-Dimensional Photonic Crystals

2010 ◽  
Vol 663-665 ◽  
pp. 725-728 ◽  
Author(s):  
Yuan Ming Huang ◽  
Qing Lan Ma ◽  
Bao Gai Zhai ◽  
Yun Gao Cai
Keyword(s):  
Photonic Crystals ◽  
Band Gap ◽  
Theoretical Calculations ◽  
Stop Band ◽  
Band Gaps ◽  
Characteristic Matrix ◽  
Frequency Range ◽  
Defect Band ◽  
One Dimensional ◽  
The One

Considered the model of the one-dimensional photonic crystals (1-D PCs) with double defects, the refractive indexes (n2’, n3’ and n2’’, n3’’) of the double defects were 2.0, 4.0 and 4.0, 2.0 respectively. With parameter n2=1.5, n3=2.5, by theoretical calculations with characteristic matrix method, the results shown that for a certain number (14 was taken) of layers of the 1-D PCs, when the double defects abutted, there was a defect band gap in the stop band gap, while when the double defects separated, there occurred two defect band gaps in the stop band gap; besides, with the separation of the two defects, the transmittance of the double defect band gaps decreased gradually. In addition, in this progress, the frequency range of the stop band gap has a little increase from 0.092 to 0.095.

Hanna Yablonka, Yeladim beseder gamur: biyografiyah dorit shel yelidei haaretz 1948–1955 (Children by the Book, Biography of a Generation: The First Native Israelis Born 1948–1955). Rishon Letziyon: Miskal, 2018. 430 pp.

2021 ◽  
pp. 310-312
Keyword(s):  
Educational System ◽  
Historical Consciousness ◽  
The State ◽  
Historical Experience ◽  
One Dimensional ◽  
The People ◽  
Native Identity ◽  
The One ◽  
State Educational ◽  
The Right

This chapter examines Hanna Yablonka's Children by the Book, Biography of a Generation: The First Native Israelis Born 1948–1955 (2018). This book is unique in that it is neither politically committed to nationalist political slogans that are thrown daily into the arena of Israeli politics in the days of Netanyahu nor connected to the one-dimensional, sweeping condemnation of critics of the Israeli enterprise on the Right and Left. Instead, it suggests to set aside, even if only for a moment, what Yablonka calls “the current Israeli discourse, which furiously shatters everything that has happened in the state since it was established, brutally erasing all the achievements of Little Israel.” Yabonka is guided by Karl Mannheim's concept of a “historical generation”: a group in which there is a shared historical consciousness derived from historical experience. She shows how the state educational system fashioned the image of the new Israeli, endowing children with a local, native identity and imbuing them with the consciousness of belonging both to the people and to the land.

scholarly journals Lipoarabinomannans: characterization of the multiacylated forms of the phosphatidyl-myo-inositol anchor by NMR spectroscopy

1999 ◽  
Vol 337 (3) ◽  
pp. 453-460 ◽  
Author(s):  
Jérôme NIGOU ◽  
Martine GILLERON ◽  
Germain PUZO
Keyword(s):  
Molecular Basis ◽  
Quantum Correlation ◽  
Analytical Approach ◽  
31P Nmr ◽  
Multiple Quantum ◽  
Double Negative ◽  
Bacillus Calmette Guerin ◽  
One Dimensional ◽  
The One

Lipoarabinomannans, which exhibit a large spectrum of immunological activities, emerge as the major antigens of mycobacterial envelopes. The lipoarabinomannan structure is based on a phosphatidyl-myo-inositol anchor whose integrity has been shown to be crucial for lipoarabinomannan biological activity and particularly for presentation to CD4/CD8 double-negative αβT cells by CD1 molecules. In this report, an analytical approach was developed for high-resolution 31P-NMR analysis of native, i.e. multiacylated, lipoarabinomannans. The one-dimensional 31P spectrum of cellular lipoarabinomannans, from Mycobacterium bovis Bacillus Calmette–Guérin, exhibited four 31P resonances typifying four types of lipoarabinomannans. Two-dimensional 1H-31P heteronuclear multiple-quantum-correlation/homonuclear Hartmann–Hahn analysis of the native molecules showed that these four types of lipoarabinomannan differed in the number and localization of fatty acids (from 1 to 4) esterifying the anchor. Besides the three acylation sites previously described, i.e. positions 1 and 2 of glycerol and 6 of the mannosyl unit linked to the C-2 of myo-inositol, we demonstrate the existence of a fourth acylation position at the C-3 of myo-inositol. We report here the first structural study of native multiacylated lipoarabinomannans, establishing the structure of the intact phosphatidyl-myo-inositol anchor. Our findings would help gain more understanding of the molecular basis of lipoarabinomannan discrimination in the binding process to CD1 molecules.

On the critical infection rate of the one-dimensional basic contact process: numerical results

1988 ◽  
Vol 25 (1) ◽  
pp. 1-8 ◽  
Author(s):  
Herbert Ziezold ◽  
Christian Grillenberger
Keyword(s):  
Markov Process ◽  
Infected Cell ◽  
Infection Rate ◽  
Lower Bounds ◽  
Contact Process ◽  
Critical Value ◽  
Critical Values ◽  
One Dimensional ◽  
The One ◽  
The Right

Instead of the basic contact process on with infection rate λ we consider for m ≧ 0 the Markov process starting with ξ0(k) = 1 for k ≧ 0 and ξ0(k)= 0 for k < 0 and with changing only those k which are at most m places to the right of the left-most infected cell. For m = 0, 1,· ··, 14 direct computations give critical values which are lower bounds for the critical value of the original basic contact process.

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