共查询到20条相似文献,搜索用时 147 毫秒
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中国科技大学超声检测实验室研制的精密声速和超声衰减自动跟踪测试仪已于去年通过省级鉴定。并投入小批量生产.该仪器在声速和超声衰减的测量原理方面进行了创新,在精密声速的测量中实现了脉冲回波重合法(PEO)和回鸣法(SA)两者优点的兼容,从而实现了精密声速的目动高精度测量癌超声衰减的测量中采取了一系列措施,提高了测量精度.仪器的另一特色是实现了精密声速和超声衰减的同时自动测量,整个测量过程用微机控制,工作软件提供了较强功能,测试结果可以显示、存储、打印,也可以根据测量要求方便地编制特定的测量软件进行定时… 相似文献
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本文利用超声脉冲反射法,对人体血管壁声衰减特性进行了离体测量,给出了人体血管壁声能量衰减参数的测量值。这对超声在医学领域的应用以及超声连体非介入血栓消溶有着十分重要的意义。 相似文献
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本文详细探讨了超声波在液体中传播速度的测量方法;利用CCD测量技术实现了超声波速度的自动化测量;设计了响应的接口电路和信号处理系统,从而大大地提高了实验测量的精度和准确度. 相似文献
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本文从换能器的互易原理出发,利用平面波自易校准法获得换能器的自由场发送电流响应.根据平面活塞型换能器的衍射规律,推导出发射声功率的表达式.由此计算互易换能器在给定驱动电流(或电压)作用下的辐射超声功率.基于上述原理,使用自易校准装置测量了互易换能器的声功率一频率曲线.估计的测量不确定优于±20%. 相似文献
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Results of radionuclide activity concentration measurements in deposition and ground-level air conducted at the station of
the Institute of Physics situated 3.5 km from the Ignalina Nuclear Power Plant (Ignalina NPP) in 2005 are analyzed. Atmospheric
depositional fluxes of 7Be, 60Co and 137Cs are estimated. Radionuclide particle deposition rates are calculated. The Hybrid Single-Particle Lagrangian Integrated
Trajectory (HYSPLIT) model of the global dispersion and deposition is used to explain variations in the 137Cs activity concentration in the ground-level air in the Ignalina NPP region in 2005. An increase in the 137Cs activity concentration of up to 17.4 μBq m−3 on 30 October-5 November is studied. Modelling results show that the Chernobyl NPP Unit 4 Sarcophagus and the radiocaesium
resuspension from the Chernobyl NPP accident polluted regions are sources of 137Cs to the environment of the Ignalina NPP. Results on solubility in water of aerosols — carriers of 137Cs — are discussed. 相似文献
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An electron gas in crossed electric and magnetic fields of arbitrary strength is considered in the framework of nonequilibrium
statistical mechanics. It is known that more than one independent frequency existing in a system, which are of comparable
magnitude, can generate coherent synergic radiation. In the present system three independent frequencies exist: viz the synchrotron
frequency due to the magnetic field, the hopping frequency due to the electric field, and the plasma frequency. It is shown
that all these can combine to generate a new synergic coherent radiation. The results also show the possibility of interpreting
the quantum nature of Hall conductance as due to density function alone. Besides these, the solution admits the Schubnikov-de
Haas oscillation of the electrical conductivity due to change in the fields. 相似文献
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Z. H. Mkhitaryan A. A. Shatveryan V. M. Aroutiounian F. V. Gasparyan 《Journal of Contemporary Physics (Armenian Academy of Sciences)》2008,43(3):131-135
Low-frequency noise, in the range 1–500 Hz, is measured at room temperature in samples of Au/PS/SCS/Al structure with a layer of porous silicon. Numerical values of the Hooge parameter αH are estimated and the dependence of αH on the composition of the gaseous environment, where the sample is placed, is determined. Possible reasons of observed high values of αH for the samples in air and of the increase in αH in conditions of gas adsorption are discussed. Introducing of carbon oxide in air changes the shape of spectrum. 相似文献
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In this paper, we investigate the data of industries in China and find that the frequency distributions of fixed assets and fixed-assets’ investment of industries obey power laws. We show that these power-law modes can be explained by the rules of the Simon Model, rather than the existing investment theories such as the classical investment theory or acceleration principle. Moreover, the mechanism of the investment distribution may be similar to the forest-fire model of self-organizing criticality. By introducing the complex system methods, this research changes the traditional opinion of the investment and gains some meaningful understanding in the dynamics of industries and the economic cycle. 相似文献
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E Kh Akhmedov 《Pramana》2000,54(1):47-63
Neutrino oscillations in matter can exhibit a specific resonance enhancement — parametric resonance, which is different from
the MSW resonance. Oscillations of atmospheric and solar neutrinos inside the earth can undergo parametric enhancement when
neutrino trajectories cross the core of the earth. In this paper we review the parametric resonance of neutrino oscillations
in matter. In particular, physical interpretation of the effect and the prospects of its experimental observation in oscillations
of solar and atmospheric neutrinos in the earth are discussed.
On leave from National Research Centre, Kurchatov Institute, Moscow 123182, Russia 相似文献
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On phase-coherence in rescattering in multiphoton ionization and in higher-order harmonic generation
Summary The recently discovered plateau and rings in high-order multiphoton ionization apparently have their origin in rescattering.
Similarly, rescattering is involved in higher-order harmonic generation. Using a simple one-dimensional model, it is shown
that the phase-coherence in this rescattering process is of considerable importance.
The authors of this paper have agreed to not receive the proofs for correction.
This work has been supported by the East-West Program of the Austrian Academy of Sciences and by the Austrian Ministry of
Science and Transportation under project no. 45.372/2-IV/6/97. One of us (JZK) acknowledges the support of the Polish Committee
of Scientific Research (grant KBN 2 P03B 007 13). 相似文献
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V. I. Nazaruk 《The European Physical Journal A - Hadrons and Nuclei》2007,31(2):177-183
The role of strong absorption of particles in intermediate and final states has been considered. The range of applicability
of phenomenological models of absorption has been studied. This model is nonuniversal. Its applicability depends on the type
of interaction Hamiltonian and matrix element used. We also demonstrate that the violation of the unitarity condition can
produce a qualitative error in the results. The absorption (decay) in the final state does not tend to suppress the total
process probability as well as the probability of the channel corresponding to absorption. This is true for the reactions,
decays and nˉ conversion in the medium. 相似文献