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1.
In magnetic bubble memory packages having a bias field HB supplied by a Ba-ferrite permanent magnet structure, the magnitude of HB may be appreciably altered after setting by transient exposure to externally applied magnetic fields Hext as much as 10 times smaller than the field used in setting HB . We examine this effect for a particular magnet design having a permalloy yoke, a gap of 0.270 inches, and a saturation fieldH_{sat} simeq 240 Oe. We find that the magnitude of the effect depends upon the ratioH_{B}/H_{sat} and upon the procedure used in setting HB . After setting toH_{B} = 200 Oe from saturation with a demagnetizing fieldH_{ext} = -1400 Oe, a remagnetizing fieldH_{ext} simeq 1800 Oe is required to increase HB by 1%. On the other hand, after setting toH_{B} = 100 Oe withH_{ext} = -2300 Oe, a remagnetizing fieldH_{ext} simeq 400 Oe is sufficient to increase HB by 1%. Setting by demagnetizing from saturation yields superior stability to setting by magnetizing from the demagnetized state, and stability of the set magnet may be further improved by demagnetizing with a ringing (alternating) field. This behavior is explained with a simple model and its importance for magnet design is discussed. 相似文献
2.
Searching for converging research using field to field citations 总被引:1,自引:0,他引:1
We define converging research as the emergence of an interdisciplinary research area from fields that did not show interdisciplinary connections before. This paper presents a process to search for converging research using journal subject categories as a proxy for fields and citations to measure interdisciplinary connections, as well as an application of this search. The search consists of two phases: a quantitative phase in which pairs of citing and cited fields are located that show a significant change in number of citations, followed by a qualitative phase in which thematic focus is sought in publications associated with located pairs. Applying this search on publications from the Web of Science published between 1995 and 2005, 38 candidate converging pairs were located, 27 of which showed thematic focus, and 20 also showed a similar focus in the other, reciprocal pair. 相似文献
3.
碳纳米管冷阴极超高真空鞍场规的电场模拟与实验研究 总被引:1,自引:0,他引:1
在静电鞍场规的基础上研制了一种碳纳米管(CNT)冷阴极鞍场规(SFG).这种冷阴极鞍场规具有电极尺寸小,吸放气率低,热效应低,功耗低的特点.本文首先计算了碳纳米管冷阴极鞍场规的电场分布,计算结果表明,二极型碳纳米管电子枪的引出栅极的正电位在低于100 V的情况下对环形阳极鞍场规的轴向电位分布影响很少;并且在现有条件下对规管参数进行了测试,实验测定的规管对空气的灵敏度是1.05 Pa-1,规管功耗由热阴极规的0.9瓦减小到7毫瓦. 相似文献
4.
针对应力场强法中场径计算方法存在争议且不易求取的问题,基于应力场强法假设,研究了场径参数计算方法的理论依据;在考虑场径求取可行性的基础上,提出一种在任意载荷条件下确定试件场径的方法.给出了场径的求取步骤,选取6块不同应力集中系数的缺口试件在4种应力比下,按照步骤求取场径.对场径计算结果拟合并作图,由图所示分析影响场径大小的因素.得出结论:在相同应力比下,场径与应力集中系数呈很强的线性关系;在相同应力集中系数下,场径与应力比呈很强的二次曲线关系.通过实例对所提出的方法进行了验证,结果表明:由提出方法确定的场径计算得出的疲劳寿命更贴近于试验寿命,在保证安全的基础上提高了疲劳寿命预测的准确性. 相似文献
5.
The damage theory is used to study the crack tip problem and the crack tip damage field is obtained. A near-field damage criterion is proposed based on micro experimental analysis. The relationship between the macro fracture parameter and the microstructure parameter of material has been obtained and proved by experimental results. 相似文献
6.
提出了一种与已知场点相关地震动场模型。将工程频段(0~25 Hz)分成若干个互不重叠的子段,在每个子频段内将地震动看作面波和体波的叠加;其次在每个子频段内确定影响合成地震动幅值谱的关键因素并将其引入模型中,使每个子频段的合成地震动幅值谱、功率谱和已知幅值谱、功率谱一致;再次由相位差谱频数分布与地震动强度包络的相似性,将决定地震动强度非平稳的关键因素即相位差谱引入到模型中,使合成地震动和已知地震动波形相似;最后,由模型中的频散曲线和距离参数描述不同场点之间的相干性,将合成地震动扩展到地震动场模型。El Centro地震波场点地震动场算例表明,模型不仅可以实现合成地震动场功率谱和已知场点完全一致,而且相干性合理,可以用于工程分析。 相似文献
7.
Electric field freezing 总被引:8,自引:0,他引:8
R. W. Smith 《Journal of Materials Science Letters》1987,6(6):643-644
8.
《Cold Regions Science and Technology》1987,14(1):95-103
Analytical aspects of interaction between an unconsolidated or poorly consolidated rubble field and a conical-type, massive, ice-resistant, bottom-founded offshore structure are presented in the paper. This matter is a substantial part of an analysis of global ice loading imposed on an offshore structure in the transition zone of the Arctic Seas. The paper contains analytical formulation of the problem and relevant analytical results which describe the geometrical aspects of the ice-structure interaction along with the global ice load which can be imposed on the structure. The results can be generalized and used for structures with arbitrary cone angles up to 90°. All results are presented in tabulated and graphical forms convenient for practical engineering applications. 相似文献
9.
Wind field simulation 总被引:7,自引:0,他引:7
An efficient algorithm to simulate turbulent, atmospheric or wind tunnel generated wind fields is devised. The method is based on a model of the spectral tensor for atmospheric surface-layer turbulence at high wind speeds and can simulate two- or three-dimensional fields of one, two or three components of the wind velocity fluctuations. The spectral tensor is compared with and adjusted to several spectral models commonly used in wind engineering. Compared to the Sandia method (see Veers, P. S., Three-dimensional wind simulation. Technical Report SAND88-0152, Sandia National Laboratories, 1988) the algorithm is more efficient, simpler to implement, and in some respects more physical. The simulation method is currently used for load calculations on wind turbines and bridges. 相似文献
10.
Terahertz pulse propagation in the near field and the far field 总被引:1,自引:0,他引:1
Gürtler A Winnewisser C Helm H Jepsen PU 《Journal of the Optical Society of America. A, Optics, image science, and vision》2000,17(1):74-83
We present a detailed investigation of the propagation properties of beams of ultrashort terahertz (THz) pulses emitted from large-aperture (LA) antennas. The large area of the emitter is demonstrated to have substantial influence on the temporal pulse profile in both the near field and the far field. We perform a numerical analysis based on scalar and vectorial broadband diffraction theory and are able to distinguish between near-field and far-field contributions to the total THz signal. We find that the THz beam from a LA antenna propagates like a Gaussian beam and that the temporal profile of the THz pulse, measured in the near field, contains information about the temporal and spatial field distribution on the emitter surface, which is intrinsically connected to the carrier dynamics of the antenna substrate. As a result of pulse reshaping, focusing of the THz beam leads to a reduced relative pulse momentum, with implications in THz field-ionization experiments. 相似文献
11.
A. R. Sabitov R. F. Sharafutdinov 《Journal of Engineering Physics and Thermophysics》1999,72(2):250-253
We carried out a numerical investigation of the temperature field arising in an oil bed due to the Joule-Thomson effect and
the heat of deaeration of the liquid in the nonstationary pressure field in displacement of oil by water. The formation of
the temperature field depends substantially on the initial flooding of the bed and the approach of the front of the displacement
of oil by water. The value of the water-oil ratio exerts an effect on the sign of the temperature anomaly at the outlet from
the bed. 相似文献
12.
采用电泳法将碳纳米管组装到电化学淀积的银台阵列上作为场发射阴极并研究了它的场发射特性.场发射特性测试结果表明:该阴极具有优异的场发射特性,开启电场为2.8V/μm,在应用电场为5.5V/μm时,发射电流密度达到1.7mA/cm2.具有优异的发射性能的原因可以归结到银台的边缘和银台类山状的表面增强了碳纳米管的场致电子发射.该阴极制备工艺简单、发射特性优异,且容易实现大面积制备,可以应用到大面积场发射显示器件中. 相似文献
13.
《NDT International》1986,19(1):3-14
Non-destructive inspection of defects using the magnetic leakage flux method presents several experimental and theoritical difficulties. It is shown that the leakage field strength around a defect is linked linearly with the field strength inside it. Thus a prerequisite to a better understanding of the phenomenon is the determination of the magnetic field strength inside the defect as a function of defect geometry, magnetic properties of the material and applied field strength. Equations are presented which enable computation of this quantity. Discrepancies between measurement and calculations using the method of finite elements emphasize the need for accurate knowledge of the magnetic field strength inside the defect. 相似文献
14.
V. I. Tokatly 《Measurement Techniques》1992,35(11):1335-1343
Translated from Izmeritel'naya Tekhnika, No. 11, pp. 55–59, November, 1992. 相似文献
15.
The NPL simulated reactor neutron field facility provides neutron spectra similar to those found in the environs of UK gas-cooled reactors. Neutrons are generated by irradiating a thick lithium-alloy target with monoenergetic protons between 2.5 and 3.5 MeV (depending on the desired spectrum), and then moderated by a 40-cm diameter sphere of heavy water. This represents an extremely soft workplace field, with a mean neutron energy of 25 keV and, more significantly, a mean fluence to ambient dose equivalent conversion coefficient of the order of 20 pSv cm(2), approximately 20 times lower than those of the ISO standard calibration sources (252)Cf and (241)Am-Be. Results of field trials are presented, including readings from neutron spectrometers, personal dosimeters (active and passive) and neutron area survey meters, and issues with beam monitoring are discussed. 相似文献
16.
Considering one-axial strain fields in the penetration depth of X-rays, the corresponding measurement distribution of e versus sin2 ψ are calculated for 24 different one-axial strains. The parameter is the measurement direction. The deformations of neighbouring points are calculated with Taylor series and described with linear expressions. There are five different types of curves, which can be combined linearly. The calculations are only applicable for plane surfaces. 相似文献
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19.
O. P. Korovin E. O. Popov V. N. Shrednik S. S. Karatetskii 《Technical Physics Letters》1999,25(4):310-312
A stable field emitter with a large tip density (up to 108 cm−2) has been created using track membrane technology. The emitter has been tested in various current collection regimes from
a constant current to short pulses of nanosecond duration with a repetition frequency of several kilohertz. The high stability
of the emission current at moderate electronic current densities up to 100 mA/cm2 is attributed to the presence of a large number of emitting tips and the dynamic equilibrium between the repulsive forces
of the electric field and the forces due to surface tension.
Pis’ma Zh. Tekh. Fiz. 25, 39–44 (April 26, 1999) 相似文献
20.
Three-dimensional external bit fields emanating from single and multiple magnetic transitions with a finite track width have been calculated. The magnetic field interferences between tracks have been also simulated. The results show that the fields have a large component in the track width direction near the transition edges. This contributes to field extension in the neighboring track direction. The amount of extension decreases with bit density increase. The results of our calculations are backed up by Lorentz microscopy observation of films in which bit fields are transcribed. 相似文献