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451.
Rohollah Fallah Madvari Mohammad Reza Monazzam Mohsen Niknam Sharak Mohsen Mosa Farkhani 《声与振动》2020,54(2):127-137
Honeycomb structures have recently, replaced with conventional homogeneous materials. Given the fact that sandwich panels containing a honeycomb
core are able to adjust geometric parameters, including internal angles, they are
suitable for acoustic control applications. The main objective of this study was
to obtain a transmission loss curve in a specific honeycomb frequency range along
with same overall dimensions and weight. In this study, a finite element model
(FEM) in ABAQUS software was used to simulate honeycomb panels, evaluate
resonant frequencies, and for acoustic analysis. This model was used to obtain
acoustic pressure and then to calculate the sound transmission loss (STL) in
MATLAB software. Vibration and acoustic analysis of panels were performed
in the frequency range of 1 to 1000 Hz. The models analyzed in this design
includes 14-single row-honeycomb designs with angles of −45°, −30°, −15°,
0°, +15°, +30°, +45°. The results showed that a-single row and −45°cell angle
honeycomb panel in the frequency range of 1 to 1000 Hz had the highest STL
as well as the highest number of frequency modes (90 mods). Furthermore, the
panel had the highest STL regarding the area under the STL curve (dB∙Hz).
The panels containing more frequency mods, have a higher transmission loss.
Moreover, the sound transmission loss is more sensitive to the cell angle variable
(θ). In other studies, the STL was more sensitive to the number of honeycomb
cells in the horizontal and vertical directions, as well as the angle of cells. 相似文献
452.
A simple, rapid and inexpensive method for separation and preconcentration of some traces of hazardous elements is presented prior to their flame atomic absorption spectrometric determinations. At pH 6.5; cadmium(II), cobalt(II) and lead(II) were separated simultaneously with 1,2‐bis((1H‐benzo[d]imidazol2‐yl)methoxy)benzene (BBIMB) as a new complexing agent and floated after adding sodium dodecyl sulfate (SDS) as a foaming reagent. The floated layer was then eluted by concentrated nitric acid in methanol and introduced to the flame atomic absorption spectrometer (FAAS). The effects of pH, concentration of BBIMB, type and amount of surfactant as the floating agent, type and amount of eluting agent and influence of foreign ions on the recoveries of the analyte ions were investigated. Also, by using a non‐linear curve fitting method the formation constants of Cd(II), Co(II) and Pb(II) complexes were obtained 1.02 × 106, 1.17 × 106 and 1.46 × 106, respectively. The detection limits of Cd(II), Co(II) and Pb(II) ions were 1.2, 0.7 and 0.5 μg/L, respectively. The enrichment factors were 45.0, 42.0 and 39.0 for Cd(II), Co(II) and Pb(II) ions, respectively. The proposed procedure was then successfully applied for determination of those heavy metals in colored human hair and dryer agents of paint samples. 相似文献
453.
Non-Newtonian ink transfer in gravure-offset printing 总被引:2,自引:0,他引:2
Fatemeh GhadiriDewan Hasan Ahmed Hyung Jin Sung Ebrahim Shirani 《International Journal of Heat and Fluid Flow》2011,32(1):308-317
The inks used in gravure-offset printing are non-Newtonian fluids with higher viscosities and lower surface tensions than Newtonian fluids. This paper examines the transfer of a non-Newtonian ink between a flat plate and a groove when the plate is moved upward with a constant velocity while the groove is held fixed. Numerical simulations were carried out with the Carreau model to explore the behavior of this non-Newtonian ink in gravure-offset printing. The volume of fluid (VOF) method was implemented to capture the interface during the ink transfer process. The effects of varying the contact angle of the ink on the flat plate and groove walls and geometrical parameters such as the groove angle and the groove depth on the breakup time of the liquid filament that forms between the plate and the groove and the ink transfer ratio were determined. Our results indicate that increasing the groove contact angle and decreasing the flat plate contact angle enhance the ink transfer ratio and the breakup time. However, increasing the groove depth and the groove angle decreases the transfer ratio and the breakup time. By optimizing these parameters, it is possible to achieve an ink transfer from the groove to the flat plate of approximately 92%. Moreover, the initial width and the vertical velocity of the neck of the ink filament have significant influences on the ink transfer ratio and the breakup time. 相似文献
454.
This review highlights the methods used for the synthesis of 3-oxo-N-(pyridin-2-yl)butanamide compounds. The reactivity and synthetic importance are investigated. In this context, recent progress in the synthesis and use of 3-oxo-N-(pyridin-2-yl)butanamide as precursors for heterocyclic compounds is reviewed. The synthetic routes for preparation of 3-oxo-N-(pyridin-2-yl)butanamide are based on the reaction of diketene with aromatic primary amine and reaction of 2-aminopyridine with β-keto-t-butylthioester or ethylacetoacetate. The bibliography includes 73 references. 相似文献
455.
N2O4 was easily impregnated on polyethyleneglycol to give a stable reagent. The polyethyleneglycol-N2O4 (PEG-N2O4) system was used as an effective nitrating agent for the nitration of phenols. Mono- and dinitrophenols can be obtained via direct nitration of phenols in the presence of PEG-N2O4 at room temperature in moderate to high yields. 相似文献
456.
An efficient one-pot three-component procedure has been developed for the preparation of tetrahydrobenzo[b]pyrans, dihydropyrano[3,2-c]chromenes, and pyrano[2,3-d]pyrimidines using nano-SiO2 as catalyst in H2O at 70 °C. This methodology has a number of advantages such as: use of reusable catalyst, easy access, short reaction times, high yields, easy work up and use of non-toxic and green solvent. 相似文献
457.
Venkata Ramaiah‐Badarla Adolfo Esteban‐Martin Majid Ebrahim‐Zadeh 《Laser \u0026amp; Photonics Reviews》2013,7(5):L55-L60
A self‐phase‐locked degenerate femtosecond optical parametric oscillator (OPO) based on the birefringent nonlinear material, bismuth triborate, BiB3O6, synchronously‐pumped by a Kerr‐lens‐mode‐locked Ti:sapphire laser at 800 nm is described. By exploiting versatile phase‐matching properties of BiB3O6, including large spectral and angular acceptance for parametric generation and low group velocity dispersion in the optical xz plane, stable self‐phase‐locked degenerate OPO operation centered at 1600 nm is demonstrated using collinear type I (e → oo) interaction in a 1.5‐mm crystal at room temperature. The degenerate OPO output spectrum extends over 46 nm (∼5.4 THz) with 190 fs pulse duration for input pump pulses of 155 fs with a bandwidth of 7 nm. Phase coherence between the pump and degenerate output is verified using f‐2f interferometry, and discrete frequency beats caused by different carrier‐envelope‐offset frequencies are measured using radio frequency measurements. Photo shows a 1.5‐mm BiB3O6 crystal used as a nonlinear gain medium in a degenerate self‐phase‐locked femtosecond OPO operating at room temperature. The green beam is the result of non‐phase‐matched sum‐frequency mixing between the pump light and the sub‐harmonic OPO field at degeneracy. 相似文献
458.
3-Aminoimidazo[1,2-a]pyridines have been synthesized in good to excellent yields in the presence of the ionic liquid 1-butyl-3-methylimidazolium bromide [bmim]Br, the reaction workup is simple and the ionic liquid can be easily separated from the product and reused. 相似文献
459.
Hashem Sharghi Khodabakhsh Niknam Ahmad Reza Massah 《Journal of heterocyclic chemistry》1999,36(3):601-606
A number of macrocyclic diamides have been synthesized from the reaction of a diacid dicarboxylic dichloride with primary diamino compound in the presence of magnesium oxide-silica gel at room temperature in good yields. Using urea and thiourea as well as diamines to produce the corresponding macrocycles in the range of 52–56% yields are also included in this paper. One of the major advantages of this method is simple regeneration of inorganic solid and its reuse through several cycles without a decrease in activity. 相似文献
460.
Let \(X\) and \(Y\) be Banach spaces, \(n\in \mathbb {N}\) , and \(B^n(X,Y)\) the space of bounded \(n\) -linear maps from \(X\times \ldots \times X\) ( \(n\) -times) into \(Y\) . The concept of hyperreflexivity has already been defined for subspaces of \(B(X,Y)\) , where \(X\) and \(Y\) are Banach spaces. We extend this concept to the subspaces of \(B^n(X,Y)\) , taking into account its \(n\) -linear structure. We then investigate when \(\mathcal {Z}^n(A,X)\) , the space of all bounded \(n\) -cocycles from a Banach algebra \(A\) into a Banach \(A\) -bimodule \(X\) , is hyperreflexive. Our approach is based on defining two notions related to a Banach algebra, namely the strong property \((\mathbb {B})\) and bounded local units, and then applying them to find uniform criterions under which \(\mathcal {Z}^n(A,X)\) is hyperreflexive. We also demonstrate that these criterions are satisfied in variety of examples including large classes of C \(^*\) -algebras and group algebras and thereby providing various examples of hyperreflexive \(n\) -cocyle spaces. One advantage of our approach is that not only we obtain the hyperreflexivity for bounded \(n\) -cocycle spaces in different cases but also our results generalize the earlier ones on the hyperreflexivity of bounded derivation spaces, i.e. when \(n=1\) , in the literature. Finally, we investigate the hereditary properties of the strong property \((\mathbb {B})\) and b.l.u. This allows us to come with more examples of bounded \(n\) -cocycle spaces which are hyperreflexive. 相似文献