共查询到20条相似文献,搜索用时 15 毫秒
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对块状TiO2气凝胶的溶胶-凝胶过程及结构进行了实验研究,结果发现:增加催化剂的量,凝胶化时间缩短,湿凝胶的透明度降低,强度提高;增加前驱体的量,凝胶化时间缩短,湿凝胶的透明度变化不大,强度提高;增加水量,凝胶化时间先缩短后增加,湿凝胶透明度先减小后增加,强度先增加后减小。利用扫描电镜对超临界干燥法制备的不同催化剂量和密度的块状TiO2气凝胶的结构进行了表征,并对结构与溶胶-凝胶过程之间的联系进行了分析。结果表明:增加催化剂量,由于缩聚反应进行的程度提高,气凝胶粒子粒径较小且总的孔径较大。减小前驱体量,气凝胶粒子粒径增大且结构逐渐疏松。 相似文献
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A. I. Parkhomenko 《JETP Letters》2001,74(3):154-158
It is shown that the velocity component transverse to the radiation propagation direction can arise in the light-induced ion drift (LIID) after applying an external magnetic field to a weakly ionized gas. It is predicted that the projection of the ion drift velocity onto the radiation direction changes its sign with an increase in the magnetic field, resulting in the anomalous LIID. 相似文献
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A technique for improving the transmission of intense electron beams through cusp magnetic field in vacuum using dielectric
drift tubes has been demonstrated. The plasma produced by the material of the dielectric tube increases the transmission efficiency
by a factor of four over vacuum values. 相似文献
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Zavattini E Zavattini G Ruoso G Polacco E Milotti E Karuza M Gastaldi U Di Domenico G Della Valle F Cimino R Carusotto S Cantatore G Bregant M;PVLAS Collaboration 《Physical review letters》2006,96(11):110406
We report the experimental observation of a light polarization rotation in vacuum in the presence of a transverse magnetic field. Assuming that data distribution is Gaussian, the average measured rotation is (3.9 +/- 0.5) x 10(-12) rad/pass, at 5 T with 44 000 passes through a 1 m long magnet, with lambda = 1064 nm. The relevance of this result in terms of the existence of a light, neutral, spin-zero particle is discussed. 相似文献
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Qin Hu 《Applied Surface Science》2010,256(20):5952-5956
To explore the machining characteristics of glassy carbon by focused ion beam (FIB), particles induced by FIB milling on glassy carbon have been studied in the current work. Nano-sized particles in the range of tens of nanometers up to 400 nm can often be found around the area subject to FIB milling. Two ion beam scanning modes - slow single scan and fast repetitive scan - have been tested. Fewer particles are found in single patterns milled in fast repetitive scan mode. For a group of test patterns milled in a sequence, it was found that a greater number of particles were deposited around sites machined early in the sequence. In situ EDX analysis of the particles showed that they were composed of C and Ga. The formation of particles is related to the debris generated at the surrounding areas, the low melting point of gallium used as FIB ion source and the high contact angle of gallium on glassy carbon induces de-wetting of Ga and the subsequent formation of Ga particles. Ultrasonic cleaning can remove over 98% of visible particles. The surface roughness (Ra) of FIB milled areas after cleaning is less than 2 nm. 相似文献
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A theoretical model has been developed which describes the critical electron emission from a dielectric that is induced by
an injected nanosecond-duration electron beam of moderate or high density. A numerical realization of the model has been constructed
which describes the principal properties of the emission: the onset of the phenomenon as the density of the charge injected
in the specimen reaches a certain value; the delay of the emission pulse relative to the exposure pulse, which may be as long
as several tens of nanoseconds; the emission coefficient reaching unity, and the spatial nonuniformity of the emission.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 61–66, August, 2008. 相似文献
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利用闭合轨道理论, 研究了变化的磁场和不同电介质表面对氢负离子光剥离截面的影响, 并推导出了该体系下的光剥离截面公式. 结果发现, 氢负离子的光剥离截面不仅与磁场的强度有关, 而且还与电介质常数有关. 当氢负离子到电介质表面的距离和电介质常数一定时, 体系的光剥离截面中的振荡随磁场的变化而明显变化. 随着磁场强度的 增大, 体系的闭合轨道数目增多, 光剥离截面的振荡越来越复杂. 当氢负离子到电介质表面的距离和磁场强度一定时, 电介质常数的变化对光剥离截面的影响也很重要, 随着电介质常数的增大, 体系的闭合轨道数目增多, 光剥离截面的振荡也变得越来越复杂. 因此, 可以通过改变磁场强度和电解质常数来调整负离子的光剥离截面. 此结果 对于研究负离子体系在表面附近和外场中的光剥离问题具有一定的参考价值. 相似文献
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A review of analytical solutions of the Vlasov equation for a beam of charged particles is given. These results are analyzed on the basis of a unified approach developed by the authors. In the context of this method, a space of integrals of motion is introduced in which the integrals of motion of particles are considered as coordinates. In this case, specifying a self-consistent distribution is reduced to defining a distribution density in this space. This approach allows us to simplify the construction and analysis of different self-consistent distributions. In particular, it is possible, in some cases, to derive new solutions by considering linear combinations of well-known solutions. This approach also makes it possible in many cases to give a visual geometric representation of self-consistent distributions in the space of integrals of motion. 相似文献
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V. S. Kovivchak T. V. Panova R. B. Burlakov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2008,2(2):286-289
The formation of metal nanoparticles in a system containing a thin metal film on a dielectric substrate and irradiated with a high-power ion beam of nanosecond duration is studied. The nanoparticle formation mechanism is discussed. 相似文献
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N. Voropajeva 《Physics letters. A》2008,372(13):2167-2171
We study the motion of charged Brownian particles in an external magnetic field. It is found that a correlation appears between the components of particle velocity in the case of anisotropic friction, approaching asymptotically zero in the stationary limit. If magnetic field is smaller compared to the critical value, determined by frictional anisotropy, the relaxation of the correlation is non-oscillating in time. However, in a larger magnetic field this relaxation becomes oscillating. The phenomenon is related to the statistical dependence of the components of transformed random force caused by the simultaneous influence of magnetic field and anisotropic dissipation. 相似文献
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N. K. Vdovicheva A. G. Sazontov V. A. Sazontov 《Radiophysics and Quantum Electronics》2007,50(2):108-122
In this paper, we propose a theoretical model of the initial stage of development of a one-sided secondary-emission (multipactor)
discharge on a dielectric surface. Consideration is based on a statistical method supported by an exact analytical solution
for the transit-time distribution function of secondary electrons. The general integral equation allowing us to determine
the stationary emission-phase distribution functions and the threshold of multiplicator onset in the presence of an external
magnetic field is formulated. It is shown that the presence of an external magnetic field can significantly change the conditions
of multipactor onset. It is found that the discharge-zone boundaries calculated within the framework of a statistical model
are in qualitative agreement with the results obtained by the Monte-Carlo method.
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Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 2, pp. 118–133, February 2007. 相似文献
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Influence of a strong magnetic field on the hydrogen molecular ion using B-spline-type basis-sets 下载免费PDF全文
《中国物理 B》2015,(12)
As an improvement on our previous work [J. Phys. B: At. Mol. Opt. Phys. 45 085101(2012)], an accurate method combining the spheroidal coordinates and B-spline basis is applied to study the ground state 1σg and low excited states1σu, 1πg,u, 1δg,u, 2σg of the H+2in magnetic fields ranging from 109Gs(1 Gs = 10-4T) to 4.414 × 1013 Gs. Comparing the one-center method used in our previous work, the present method has a higher precision with a shorter computing time.Equilibrium distances of the states of the H+2in strong magnetic fields were found to be accurate to 3~5 significant digits(s.d.) and the total energies 6~11 s.d., even for some antibonding state, such as 1πg, which is difficult for the one-center method to give reliable results while the field strength is B ≥ 1013 Gs. For the large disagreement in previous works, such as the equilibrium distances of the 1πg state at B = 109 Gs, the present data may be used as a reference. Further, the potential energy curves(PECs) and the electronic probability density distributions(EPDDs) of the bound states 1σg, 1πu, 1δg and antibonding states 1σu, 1πg, 1δu for B = 1, 10, 100, 1000 a.u.(atomic unit) are compared, so that the different influences of the magnetic fields on the chemical bonds of the bound states and antibonding states are discussed in detail. 相似文献
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根据离子与径向磁场的约束关系,用面向对象的单元粒子法模拟了极向偏转器中等离子体束流在均匀和非均匀径向磁场中的运动情况,得到了在磁边界效应下极向偏转器内部畸变电场的分布,分析了对质量分离的影响。模拟成果对质量分离器、质谱分析仪及材料提纯等装置的研制、特殊位形电磁场控制多质量束流等相关领域的研究有参考价值。 相似文献
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Influence of bias magnetic field on the vacuum arc in double‐break vacuum circuit breakers 下载免费PDF全文
When double‐break vacuum circuit breakers (VCBs) interrupt the fault current, the series arc will generate their individual magnetic fields in different breaks. The magnetic field in one break will influence the arc in another break if the magnetic field is strong enough or the two breaks are very close. In this case, an interactive magnetic field effect happens. This field is also called the bias magnetic field (BMF). BMF can cause anode erosion and affect the performance at current zero. The distribution of BMF and the optimal configuration of the double‐break VCBs were obtained by the electromagnetic field simulation using the Ansoft Maxwell software. Based on the simulated magnetic field data, in the experiments, the interaction between the series vacuum arcs in double‐break VCBs was equivalent to the interaction between a single vacuum arc and the magnetic field generated by a Helmholtz coil. A high‐speed CMOS camera was used to record the trajectory of the vacuum arc plasma under different BMFs with different types of contacts. The results show the BMF can increase the arc voltage, and the arc becomes unstable. When the BMF becomes stronger, the arc voltage increases, and the arc becomes more unstable. In addition, for different types of contacts, the development process of the arc and the influence level are different under the same BMF. For a Wan‐type transverse magnetic field (TMF) contact or strong BMF, metal sputtering is evident and anode erosion becomes serious. For a cup‐type axial magnetic field (AMF) contact, the influence of BMF on the series arc plasma in double‐break VCBs is less than that of the Wan‐type TMF contact. The results of this work may be helpful for the design of compact double‐break VCBs. 相似文献
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N. I. Shtepa 《Technical Physics》2000,45(3):349-350
A way of simultaneously focusing a circular uniform beam of fine uncharged diamagnetic particles in the longitudinal and transverse directions is explored. Focusing is performed by a short magnetic lens and a diaphragm providing a time-dependent electric field. The size of the particles is within the range of 10−4–10−1 cm. 相似文献