共查询到20条相似文献,搜索用时 15 毫秒
1.
ε-caprolactam (CL) polymerization to polyamide-6 (Nylon 6) was studied at different contents of water in CL (0.01–2 wt%), with or without ε-amino-caproic acid (ACA) as an activator, applying to the mixture an initial treatment of Ultrasound (US) (17.5–20 kHz) at low temperatures (70–110 °C) and for short times (max 10 min). It was verified that polymerization at 260 °C produces a polymer having a much higher molecular weight (MW) when US is applied with respect to silent (SIL) conditions i.e. without the use of ultrasound. This constitutes a “pre-sonication effect”. The ratio (MW)US/(MW)SIL is inversely proportional to the initial content of water in CL. The action of US converts CL at very low temperatures (70–110 °C) and water content, in comparison with silent conditions where CL was unconverted.
Optimized conditions are studied with respect to nature and pressure of gas inside the reactor, temperature, time and frequency of US irradiation, energy consumption and nature of activator. 相似文献
2.
3.
Recently, a spatial compounding ultrasound imaging method was presented that utilizes a conventional 64-element phased array transducer with two unfocused pistons, each placed at one of the sides of the phased array transducer. This method is augmented here by inclusion of nonlinear filtering of the compounded images. The combined effects of the specific spatial compounding and nonlinear filtering on speckle reduction in the generated ultrasound images are studied and evaluated in two stages: First, the image quality is studied when nonlinear filtering is used as part of the spatial compounding. The study is performed by simulations using the Field II program, by processing several B-mode images of a kidney. The second stage compares the results obtained by the simulations to those obtained by in vitro laboratory experiments. Five different compounding strategies and two nonlinear filters, Gaussian and anisotropic diffusion, are investigated and evaluated in terms of image quality parameters-contrast and signal-to-noise ratio. It is shown that the combination of "averaging+nonlinear Gaussian filtering" produces the greatest improvement of image quality. When compared to a conventional phased array imaging system, the spatial compounding method that includes the conventional 64-element phased array transducer with two unfocused pistons, and employs the "averaging+nonlinear Gaussian filtering" strategy, obtains improvement in SNR that has reached 334%. Thus, though this method necessitates a somewhat wider probe, it produces significantly improved images. 相似文献
4.
单片机在"利用霍尔效应测磁场"实验中的应用 总被引:2,自引:1,他引:1
介绍了霍尔元件测磁场实验中的一种软件温度补偿方法,它利用单片机的强大软件功能,原理简单,成本低,精度高,取得了理想的测量和控制效果. 相似文献
5.
In this paper we construct the perturbative expansion for the Feynman propagation kernel of a Yang-Mills theory in the A0 = 0 gauge in any external charge sector, by using the expression of the kernel derived in a previous paper. Unlike the usual one, in this formulation of perturbation theory there are no spurious poles at zero energy transfer in the (effective) gauge field propagator. Examples of calculations of the static potential between external (infinitely heavy) non-abelian charges and of scattering amplitudes are discussed in detail. 相似文献
6.
I. K. Tokhadze T. D. Kolomiĭtsova K. G. Tokhadze D. N. Shchepkin 《Optics and Spectroscopy》2007,102(3):396-407
The IR absorption spectra of (SF6)2 dimers in Ar and N2 matrices are investigated at 11 K. As a result of the resonance dipole-dipole interaction, the band of the triply degenerate vibration v 3 is split into two components v X, Y and v Z. In comparison with the gaseous state, the splitting Δv = v X, Y ? v Z in the argon matrix decreases to 18.45 cm?1, whereas, in the nitrogen matrix, the band v X, Y is split into components v X and v Y, with the splitting being equal to δ ≈ 0.9 cm?1. A model that takes into account the influence of the matrix on the spectra of dimers is developed. The model makes it possible to successively (i) calculate the resonance spectrum of an isolated dimer in terms of the model of local modes taking into account resonance interactions, (ii) determine with the help of the Monte Carlo method the structure of a matrix consisting of 512–1440 Ar (or N2) atoms and a rigid (SF6)2 dimer, and (iii) take into account interactions of local dipole moments of a dimer with particles of the matrix in the approximation of dipole-induced dipole interactions. The model developed satisfactorily describes the experimental results. The calculated frequencies v Z, v X, and v Y of a dimer in the matrix are shifted toward smaller frequencies as compared to the gaseous state, while the resonance splitting decreases virtually by 2 cm?1. It is shown that, in an argon matrix with a symmetric arrangement of argon atoms nearest to a dimer, the splitting of v X, Y proves to be smaller than 0.05 cm?1. In a nitrogen matrix, this splitting increases virtually to 0.4 cm?1. 相似文献
7.
Mandroyan A Doche ML Hihn JY Viennet R Bailly Y Simonin L 《Ultrasonics sonochemistry》2009,16(1):97-104
Sonoelectrochemical experiments differ from sonochemical ones by the introduction of electrodes in the sonicated reaction vessel. The aim of the study is to characterize the changes in the ultrasonic activity induced by the presence of an electrode located in front of the transducer. The scope of our investigations concerns two low frequency vibration modes: 20 and 40 kHz. For this purpose, two laser visualization techniques have been used. The first part of the study, described in a previous paper (Part I), deals with the laser tomography technique which provides an accurate picture of the reactor active zones, related to numerous cavitation events. The second part of the paper (Part II) will describe the particle image velocimetry (PIV) technique used to measure the velocity vector field in the fluid portion between the horn and the electrode. As for the previous study, two parameters were studied: the electrical power supplied to the transducer and the electrode/transducer distance. The velocity vector fields show a main flow in the reactor axis. This flow seems to correspond to the conical cavitation bubbles structure which is observed on the laser tomography pictures. When an electrode is introduced into the reactor, two additional symmetric transversal flows can be quantified on both sides of the electrode. 相似文献
8.
In a previous paper second-order calculations were carried out on the two-level pairing force model using perturbation theory for projected states and the results were compared with those of BCS or ordinary perturbation theory. In the present paper criteria for convergence are applied to two different forms of the perturbation series for both the projected and ordinary perturbation theories. It is found that the superior results obtained for the convergence rates in the projected theory tally neatly with the results of the second-order calculations, and give further support to the use of the projected perturbation theory. 相似文献
9.
《Nuclear Physics A》1986,453(3):365-388
The three-body α + 2N model developed in our earlier works to describe the ground states of the A = 6 nuclei is generalized here to describe the spectrum of the low-lying states of these nuclei. The levels of the nuclei are shown to be differently sensitive to the various Nα interaction components, whence some conclusions concerning the true form of the Nα interaction are drawn. The geometric structure of the 6Li and 6He ground states is studied in detail. A significant contribution of the stretched cigar-shaped three-particle configuration NαN with an α-particle between two nucleons has been found. The wave functions of the ground and excited states of the A = 6 nuclei are tabulated. The wave functions found have been tested carefully using numerous experimental data. 相似文献
10.
J. Kim 《Applied Surface Science》2005,252(5):1305-1312
The methods of X-ray photoelectron spectroscopy (XPS), secondary-ion mass spectrometry (SIMS), and scanning electron microscopy (SEM) have been used to investigate aspects of the bonding of bis-1,2-(triethoxysilyl)ethane (BTSE) onto anodized samples of 7075-T6 aluminum alloy that have been subjected to the various pre-treatments considered in Part I. The oxide layer thins when this sample is subjected to a Forest Products Laboratory (FPL) treatment; topographical changes are detected by SEM after only 5 min, and the “scallop structures” increase in size for longer times of the FPL treatment. These 7075-Al surfaces adsorb more BTSE than the high-purity Al samples considered in Part I, although the interfacial bonding indicated by the [AlOSi]+/[Al2O]+ SIMS ratios measured for the former samples are constant for different times of FPL treatment, unlike the situation for high-purity Al. Heating anodized 7075-Al samples, either before or after FPL treatment, has no significant effect on the subsequent BTSE adsorption, but a H2 plasma treatment can enhance the interfacial Al-O-Si bonding with a decrease in the total BTSE polymerization. 相似文献
11.
用密度泛函理论DFT方法,计算研究不对称簇合物(HFGaN_3)_n(n=1-6)的几何构型、稳定性、IR谱和热力学性质.结果表明,簇合物(HFGaN_3)_n(n=2-6)的优化构型拥有一个Ga和α-N原子交替的2n元环状结构.通过计算研究(HFGaN_3)_n(n=1-6)的平均结合能、二阶能量差分和能隙与团簇尺寸关系,发现后两者表现出明显的"奇—偶"振荡现象.对计算获得的IR谱进行归属,获得四个特征区.讨论了团簇尺寸和温度对(HFGaN_3)_n(n=1-6)热力学函数的影响.由焓变和吉布斯自由能可知,200-800K温度范围内由单体形成稳定的多聚体(HFGaN_3)_n(n=2-6)在热力学上有利. 相似文献
12.
13.
A.S. Akhtar 《Applied Surface Science》2006,253(2):502-509
Coatings formed on 2024-T3 aluminum alloy were studied by scanning electron microscopy (SEM) and scanning Auger microscopy (SAM) after dipping in zinc phosphating (ZPO) baths at different acidities, with or without the Ni2+ additive. The objective was to learn more about the ZPO coating mechanism on the different microstructural regions of 2024-T3. When the initial coating solution pH is 4 (optimal acidity), a slower etching rate at the Al-Cu-Fe-Mn intermetallic particle causes significant precipitation of ZnO, which differs from the coating on other regions of the surface where phosphate predominates. The larger crystals (∼μm dimension) on the matrix and the Al-Cu-Mg particle contain more phosphate compared to other areas on the surface. When Ni2+ is added to the coating solution, the Al-Cu-Mg particle is more thickly coated compared to when the Ni2+ is not present. The slower rate of precipitation when Ni2+ is present in the coating solution increases the exposure of the alloy substrate to the acidic environment, so allowing more dissolution of Mg and Al from the Al-Cu-Mg particle. This results in the particle becoming more cathodic in nature, and therefore more coating deposits at this location. Evidence from SAM supports the presence of NiAl2O4, hypothesized in Part I, forming at coating pores later in the process. 相似文献
14.
15.
The dispersion polymerization of styrene has been carried out using polystyrene-block-poly(4-vinylpyridine) copolymer [P(S-b-4VP)], prepared by a reversible addition-fragmentation chain transfer (RAFT) method, as a steric stabilizer in alcohol media. These block copolymer contains a long poly(4-vinylpyridine) block and a short polystyrene block. The stable spherical particles were obtained when the block copolymer concentrations increased from 2 to 20 wt.% relative to the monomer and the average particle sizes decreased from 340 to 200 nm with increasing concentration of the block copolymer. Alcoholic solvents, from methanol to n-hexanol, are responsible for the particle size. These results indicate that the poly(S-b-4VP) block copolymer is effective for providing polystyrene nano-sized particles with a low content of it working as a good stabilizer in any kind of alcoholic medium. 相似文献
16.
《Comptes Rendus Physique》2014,15(10):859-865
The investigation of non-reciprocal behavior of optical beams in a rotating reference frame was the main motivation of the historic tabletop experiment of George Sagnac. His ground-breaking experiment was extended to a very large installation more than a decade later, which was sensitive enough to allow Michelson, Pearson and Gale to resolve the rotation rate of the Earth by an optical interferometer. With the advent of lasers in the early sixties of the last century, rotating laser cavities with a ring structure demonstrated superior performance and very soon matured to a point where mechanical gyroscopes were quickly superseded by laser gyroscopes in aircraft navigation. When vastly upscaled ring lasers were taken back to the laboratory at the end of the 20th century, the goal of applying the Sagnac effect to geodesy for the monitoring of tiny variations of Earth's rotation was the main motivation. The large-ring laser G, which is the most stable instrument out of a series of instruments built by the New Zealand–German collaboration, routinely resolves the rotation rate of the Earth to better than eight orders of magnitude. Since G is directly referenced to the Earth rotation axis, the effect of diurnal polar motion, the Chandler and the Annual wobbles as well as tilts from the solid Earth tides can be found in the interferogram obtained from the ring laser. G has also demonstrated high sensitivity to rotations associated with seismic events. The toroidal eigenmodes of the Earth when they are excited by large earthquakes have been resolved. A surprisingly large amplitude has been measured for Love wave signals contained in the microseismic background signal. This paper summarizes the recent development of highly sensitive large Sagnac gyroscopes, and presents unique results from the measurements of rotations of the earth. 相似文献
17.
Here is the review of experimental and theoretical results on the mechanism of heat transfer in nanofluids. A wide scope of
problems related to the technology of nanofluid production, experimental equipment, and features of measurement methods is
considered. Experimental data on heat conductivity of nanofluids with different concentrations, sizes, and material of nanoparticles
are presented. Results on forced and free convection in laminar, and turbulent flows are analyzed. The available models of
physical mechanisms of heat transfer intensification and suppression in nanofluids are presented. There are significant divergences
in data of different researchers; possible reasons for this divergence are analyzed. 相似文献
18.
19.
M. Micklinghoff 《Nuclear Physics A》1978,295(2):237-255
Starting from the conventional shell model, different methods for the treatment of the continuum are given. Using the modified continuum states of part I together with the reaction operator formalism, the present approach unifies the numerical features of the R-matrix theory and the physical picture of the shell model. As it treats the bound states and the scattering states in the same basis we calculated both for the 12C + n system as a test case. It is found that the results resemble the experimental data quite well, including for the first time the negative-parity resonances. 相似文献
20.
M. S. Kalenkov 《Journal of Experimental and Theoretical Physics》2002,95(2):348-353
A nonlinear correction to the magnetic penetration depth into a \(d_{x^2 - y^2 } \)-wave superconductor is found that takes into account nonlocal effects. The calculation is carried out for the self-consistent distribution of the screening supercurrent. An analytical expression for the nonlinear correction is obtained in the limit of the pure superconductor for orientations that do not admit the formation of surface states. It is shown that the presence of unitary impurities makes the nonlinear Meissner effect unobservable in the nonlocal regime for almost all orientations of the crystal either due to the suppression of the nonlocal response of quasi-particles by impurities or due to a considerable contribution of Andreev low-energy surface states to the penetration depth. In the Born scattering limit, there exists a broad interval of orientations and mean free paths in which the non-locality of the response must be taken into account in the calculation of the nonlinear correction to the penetration depth at rather low temperatures. 相似文献