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991.
Polymethyl methacrylate modified carbon nanotubes were prepared using γ radiation, and the modified carbon nanotubes exhibited
strong luminescence (∼
∼568 nm) at room temperature and an absorption peak at ∼
∼247 nm can be observed in the polymer modified samples. 相似文献
992.
Jean E. Burns 《Foundations of Physics》2007,37(12):1727-1737
Vacuum radiation causes a particle to make a random walk about its dynamical trajectory. In this random walk the root mean
square change in spatial coordinate is proportional to t
1/2, and the fractional changes in momentum and energy are proportional to t
−1/2, where t is time. Thus the exchange of energy and momentum between a particle and the vacuum tends to zero over time. At the end of
a mean free path the fractional change in momentum of a particle in a gas is very small. However, at the end of the mean free
path each particle undergoes an interaction that magnifies the preceding change, and the net result is that the momentum distribution
of the particles in a gas is randomized in a few collision times. In this way the random action of vacuum radiation and its
subsequent magnification by molecular interaction produces entropy increase. This process justifies the assumption of molecular
chaos used in the Boltzmann transport equation. 相似文献
993.
D. V. Barishpol’tsev S. Yu. Gus’kov E. M. Ivanov P. S. Kotegov V. B. Rozanov 《Journal of Russian Laser Research》2007,28(4):357-371
Analytical relationships between the photon-emission probability from a surface and the optical thickness along with analytical
relationships between the spectral brightness of a homogeneous plasma of spherical geometry are derived with taking into account
the radiation absorption. The photon-emission probability and the spectral brightness are also obtained for a plasma of cylindrical
geometry and a plasma consisting of spherical layers. The relationships are given in the integral form, while attempts to
find them analytically, i.e., to calculate the integrals, failed. However, they can be computed numerically. The formula for
spectral brightness is derived for the case of radiation of two flat layers, which differ by the structure, thickness, and
thermodynamic and spectral characteristics. The expressions for the spherical and flat layers are compared. The ratio of the
dimensions permitted to approximate the flat case by the spherical case is found. The criteria of applicability and accuracy
of such approximation have been elaborated. As examples of the application of the expressions derived, the radiation spectra
of the aluminum, carbon, copper, and oxygen plasmas were calculated and plotted.
__________
Translated from Preprint No. 33 of the P. N. Lebedev Physical Institute, Moscow (2006). 相似文献
994.
Hawking radiation can be viewed as a process of quantum tunnelling near black hole horizon. When a particle with angular momentum
tunnels across the event horizon of Schwarzschild black hole, the black hole will change into a Kerr black hole. The emission
rate of the massless particles with angular momentum is calculated, and the result is consistent with an underlying unitary
theory. 相似文献
995.
William H. Massover 《Journal of synchrotron radiation》2007,14(1):116-127
Recent research progress using X‐ray cryo‐crystallography with the photon beams from third‐generation synchrotron sources has resulted in recognition that this intense radiation commonly damages protein samples even when they are held at 100 K. Other structural biologists examining thin protein crystals or single particle specimens encounter similar radiation damage problems during electron diffraction and imaging, but have developed some effective countermeasures. The aim of this concise review is to examine whether analogous approaches can be utilized to alleviate the X‐ray radiation damage problem in synchrotron macromolecular crystallography. The critical discussion of this question is preceded by presentation of background material on modern technical procedures with electron beam instruments using 300–400 kV accelerating voltage, low‐dose exposures for data recording, and protection of protein specimens by cryogenic cooling; these practical approaches to dealing with electron radiation damage currently permit best resolution levels of 6 Å (0.6 nm) for single particle specimens, and of 1.9 Å for two‐dimensional membrane protein crystals. Final determination of the potential effectiveness and practical value of using such new or unconventional ideas will necessitate showing, by experimental testing, that these produce significantly improved protection of three‐dimensional protein crystals during synchrotron X‐ray diffraction. 相似文献
996.
We investigate the TEA CO2 laser ablation of films of poly(methyl methacrylate), PMMA, with average MW 2.5, 120 and 996 kDa doped with photosensitive compounds iodo-naphthalene (NapI) and iodo-phenanthrene (PhenI) by examining the induced morphological and physicochemical modifications. The films casted on CaF2 substrates were irradiated with a pulsed CO2 laser (10P(20) line at 10.59 μm) in resonance with vibrational modes of PMMA and of the dopants at fluences up to 6 J/cm2. Laser induced fluorescence probing of photoproducts in a pump and probe configuration is carried out at 266 nm. Formation of naphthalene (NapH) and phenanthrene (PhenH) is observed in NapI and PhenI doped PMMA, respectively, with relatively higher yields in high MW polymer, in similarity with results obtained previously upon irradiation in the UV at 248 nm. Above threshold, formation of photoproducts is nearly complete after 200 ms. As established via optical microscopy, bubbles are formed in the irradiated areas with sizes that depend on polymer MW and filaments are observed to be ejected out of the irradiated volume in the samples made with high MW polymer. The implications of these results for the mechanisms of polymer IR laser ablation are discussed and compared with UV range studies. 相似文献
997.
Vanadium oxide thin films were prepared by sol-gel method, then subjected to Nd:YAG laser (CW, 1064 nm) radiation. The characteristics of the films were changed by varying the intensity of the laser radiation. The nanocrystalline films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). XRD revealed that above 102 W/cm2 the original xerogel structure disappears and above 129 W/cm2 the films become totally polycrystalline with an orthorhombic structure. From TEM observations, we can see that due to laser radiation, the originally fibrillar-like particles disappear and irregular shaped, layer structured V2O5 particles are created. From XPS spectra we can conclude that due to laser radiation the O/V ratio increased with higher intensities. 相似文献
998.
上海光源X射线成像光束线采用多极扭摆器(wiggler)作为辐射光源, 提出一种劳厄双弯晶单色器的设计方案. 计算结果显示, 可获得固定出口的平行单色光束, 能量调谐范围覆盖19—120keV, 在33keV时, 输出光子通量及通量密度分别为1.9×1013phs/s和3.8×1010phs/s/mm2. 分析了劳厄晶体的聚焦及单色化性能, 计算了输出光子通量及单色器的热负载情况. 与传统的双平晶方案相比, 本设计在获得高通量和解决热负载等方面有明显的优越性, 并能有效控制热形变. 相似文献
999.
1000.
通过对有限紧致空间中辐射场的研究来讨论腔中的原子-辐射场耦合系统. 利用T(1)×SO(4)群的表示, 给出了辐射场的单粒子波函数以及相应的色散关系. 由此详细讨论了紧致空间中辐射场的玻色-爱因斯坦统计. 发现其性质与空间的几何性质(曲率半径)有显著的依赖关系, 并表现与通常黑体辐射系统的显著差异. 相似文献