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1.
The anatomy and functions of the blood and lymph vessels of human skin are described. Variation in these due to site, ageing and events during life consequent to exposure to a threatening environment are emphasised. Gradual atrophy and greater heterogeneity are features of ageing. Responses to injury and repair are complex and the interaction of mechanical signals distorting skin cells with numerous chemical signals are referred to. The lymphatics are part of an immunosurveillance system to monitor skin barrier penetration. The review attempts to draw attention to key recent advances in our understanding of the cytokine and growth factor production of the skin in the context of previous mainly physiological reviews especially influenced by 50 years of clinical practice as a dermatologist with an eye on both the skin and the fields of microcirculation and lymphology.  相似文献   

2.
分析了分光计中望远镜调节原理,归纳与总结了望远镜光轴、载物台都垂直于分光计中心轴的多种调节方法,有利于实验教学。  相似文献   

3.
4.
光子晶体理论应用于光纤布拉格光栅的研究   总被引:6,自引:0,他引:6  
王智  任国斌  裴丽  娄淑琴  简水生 《光学学报》2003,23(11):291-1295
将光纤布拉格光栅近似为一维光子晶体,研究光栅的能带结构和光学传输特性。利用平面波展开法对光子晶体进行理论研究,将研究方法移植到光纤布拉格光栅上,并对其进行数值分析,得到光栅的传输特性。研究表明,光栅反射谱有多个反射峰,峰值中心频率是基频的整数倍,而且峰值处存在光子带隙,反射峰带宽对应光子带隙宽度,中心频率和带宽随光栅长度、高介电常量材料占空比、调制深度而变化。结果与传统的耦合模理论一致。  相似文献   

5.
Aspects of particle physics are reviewed from an experimental viewpoint. The elementary constituents of the Universe are described, as are the fundamental forces through which they interact. Recent results are emphasized and there is some speculation about the future. No attempt has been made to give a complete bibliography, but a few references to recent reviews and original articles are given. A glossary of acronyms is included.  相似文献   

6.
The detailed group structure of the independent-particle hamiltonian is derived in terms of interior and exterior products of groups describing various types of symmetry operations which commute with the hamiltonian. Modifications of this group due to external fields are examined, as are the concepts of the equivalence of particles. Simplifications due to isomorphisms and homomorphisms are outlined. Applications involving representations within this construction are examined.  相似文献   

7.
In this work we study in detail the connection between the solutions to the Dirac and Weyl equations and the associated electromagnetic four-potentials.First,it is proven that all solutions to the Weyl equation are degenerate,in the sense that they correspond to an infinite number of electromagnetic four-potentials.As far as the solutions to the Dirac equation are concerned,it is shown that they can be classified into two classes.The elements of the first class correspond to one and only one four-potential,and are called non-degenerate Dirac solutions.On the other hand,the elements of the second class correspond to an infinite number of four-potentials,and are called degenerate Dirac solutions.Further,it is proven that at least two of these fourpotentials are gauge-inequivalent,corresponding to different electromagnetic fields.In order to illustrate this particularly important result we have studied the degenerate solutions to the forcefree Dirac equation and shown that they correspond to massless particles.We have also provided explicit examples regarding solutions to the force-free Weyl equation and the Weyl equation for a constant magnetic field.In all cases we have calculated the infinite number of different electromagnetic fields corresponding to these solutions.Finally,we have discussed potential applications of our results in cosmology,materials science and nanoelectronics.  相似文献   

8.
肖伯钧 《大学物理》2003,22(5):22-24
讨论了银道面内的引力场强分布和太阳在银河系中所受引力与到银心距离r的关系,指出引力场强g并不是与r的平方成反比,这是由于银河系的大小和形状不能忽略造成的.强调了万有引力定律的适用条件.  相似文献   

9.
Two most important characteristics of a light scattering instrument for the measurement of the microparticle parameters in emulsions and gases are discussed. These characteristics are the resolution and the accuracy of particle size measurement. In order to obtain the most reliable data, likely interpretation methods of the measurement results are compared.  相似文献   

10.
The coefficients of the Finslerian parallel displacement along the paths of the Randers space are calculated. These are then used to define and to investigate the proper rest frame of the charged particle.  相似文献   

11.
瞬态电磁场对多孔洞目标耦合规律的数值研究   总被引:3,自引:2,他引:1       下载免费PDF全文
 运用时域有限差分(FDTD)方法,用数值方法研究了瞬态电磁场对开有多个孔洞的长方体的耦合规律。分别分析了不同极化方向、不同入射方向及不同带宽的瞬态电磁场的耦合效应。入射波极化方向与孔洞的短边平行时耦合入腔体的能量最多;相同振幅、不同上升前沿和带宽的入射波以窄带、快前沿耦合入的能量为多;多孔洞腔体内场衰减很快。  相似文献   

12.
Quantum transitions in the localized multiparticle system are considered. Constraints on the system and on the external perturbation are presented for the case, where the transitions are identical to those in the one-particle system.  相似文献   

13.
非简谐振动对石墨烯杨氏模量与声子频率的影响   总被引:1,自引:0,他引:1       下载免费PDF全文
程正富  郑瑞伦 《物理学报》2016,65(10):104701-104701
在哈里森键联轨道法框架下, 考虑到原子的短程相互作用和原子的非简谐振动, 应用固体物理理论和方法, 得到了石墨烯的力常数、杨氏模量、扭曲模量、泊松系数以及声子频率随温度的变化关系, 探讨了非简谐振动对它们的影响. 结果表明: 1)杨氏模量与声子频率等随温度变化并遵从一定的规律, 其中力常数、杨氏模量、扭曲模量随温度升高而增大, 但变化较小; 声子频率随温度升高而增大但变化较快; 泊松系数随温度升高而较快地减小; 2)石墨烯原子具有沿键长方向的纵振动和垂直键长方向的横振动, 但以纵振动为主, 纵振动的非简谐效应远大于横振动, 横振动的简谐系数ε0' 和第二非谐系数ε2' 均小于纵振动的相应值ε02; 比值为ε00' ≈ 8.477,ε22' ≈ 156; 3)若不考虑非简谐振动项, 则石墨烯的力常数、杨氏模量和扭曲模量、泊松系数、声子频率均为常量, 与实验不符合; 同时考虑到原子的第一、二非简谐振动项后, 它们均随温度升高而变化, 而且温度愈高, 原子振动的非简谐效应愈显著. 本文的结果与文献的实验结果符合较好.  相似文献   

14.
In this paper we describe experiments conducted with high-power lasers that are attempting to replicate, for a very short time and in miniature, conditions found in the Sun. Experiments to date have reached conditions in the outer part of the Sun. To reach the Sun's centre requires compression of material to very much greater than solid density and heating to over ten million degrees. To achieve this, a new class of experiments and a new generation of high-power lasers are required.  相似文献   

15.
Algebraic functions are used to provide an example of multiple-valued functions which coincide with a model (single-valued) free energy on one sheet of the Riemann surface in the neighborhood of a critical point. For the case of homogeneous free energies andα=α′=0, there are enough conditions to determine the behavior of the nearest singularities (branch points) to the critical point of the algebraic function. If no other singularities are present these branch points would represent the spinodal line. The particular exponents of the two-dimensional Ising model are used to provide a specific example.  相似文献   

16.
Theoretical calculations of equilibrium deformations and multipole moments of rare earth nuclei are presented. Good agreement with experiment for the centre of the rare earth region is found, but there are large discrepancies for the heavy Hf, W and Os isotopes and some light Sm and Gd nuclei. These discrepancies are related to hexadecapole moments and deformations. The assumption of a “partial bubble” like density distribution, as suggested by electron scattering measurements, is found to be insufficient to explain this hexadecapole anomaly. The inclusion of non-axial and hexadecapole degrees of freedom in processing the experimental data, as well as in performing theoretical calculations, is found to be the most promising approach to explaining the hexadecapole anomaly.  相似文献   

17.
《Physics letters. A》1986,117(9):433-435
A recent claim by De Muynck that the Bell inequalities are completely irrelevant to the locality problem is opposed. The various ways in which the inequalities are relevant and not relevant are briefly discussed.  相似文献   

18.
In the coherent potential approximation, the densities of electron states of binary alloys of transition elements with short-range order are obtained. These calculations are used to determine the contribution of the band-structure energy to the configuration part of the total energy, and the equilibrium values of the order parameter are calculated on the first coordination sphere. In the majority of the considered systems, the signs found for the order parameters agree with the experimental data.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 16–21, November, 1980.  相似文献   

19.
Criteria are given for the applicability of the asymptotic freedom of QCD. Perturbative QCD has a much broader range of utility than lightcone dominated phenomena. The most striking predictions pertain to transverse momenta that scale, i.e. grow proportionately to the large invariants. While hints of these unlimited transverse momenta are already visible in existing data, the predictions are unmistakable for μ-p, e+-e, and hadron-hadron experiments now planned.  相似文献   

20.
This study investigates whether the market share leader in the notebook industry in Taiwan is likely to maintain its dominant position. Market share data are used to investigate the intensity of competitiveness in the industry, and data on the gap in market shares are employed to elucidate the dominance of the leading firm in Taiwan's notebook industry during the 1998-2004 period. The newly developed Panel SURADF tests advanced by Breuer et al. [Misleading inferences from panel unit root tests with an illustration from purchasing power parity, Rev. Int. Econ. 9 (3) (2001) 482-493] are employed to determine whether the market share gap is stationary or not. Unlike other panel-based unit root tests which are joint tests of a unit root for all members of a panel and are incapable of determining the mix of I(0) and I(1) series in a panel setting, the Panel SURADF tests have the advantage of being able to investigate a separate unit root null hypothesis for each individual panel member and are, therefore, able to identify how many and which series in a panel are stationary processes. The empirical results from several panel-based unit root tests substantiate that the market shares of the firms studied here are non-stationary, indicating that Taiwan's notebook industry is highly competitive; however, Breuer et al.'s [12] Panel SURADF tests unequivocally show that only Compal is stationary with respect to market share gap. In terms of sales volume, Compal is the second largest firm in the notebook industry in Taiwan, and the results indicate that it alone has the opportunity to become the market share leader in the notebook industry.  相似文献   

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