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1.
Theeraphong Chanpheng Hitoshi Yamada Toshio Miyata Hiroshi Katsuchi 《Applied Acoustics》2004,65(2):109-123
Low-frequency noise radiated from highway bridges is a serious environmental problem in Japan. Although the suppression of bridge vibration as usually done in practice can alleviate the radiation, it may not be optimal because the behavior of radiation is not taken into consideration. Concept of radiation modes, which can represent both vibration and radiation behavior, is adapted to a highway bridge. The objectives of this paper are to study the benefits of using radiation modes in (1) identification of low-frequency noise characteristics and (2) active control of low-frequency noise radiation. Numerical study shows that the radiation modes enable radiation characteristics of low-frequency noise to be physically understood and the active controller designed by radiation modes is superior to the controller designed without considering radiation behavior. Because the concept of radiation modes can reveal the mechanics of radiation/vibration, it is appropriate to the problem of low-frequency noise radiated from highway bridges. 相似文献
2.
Timothy H. Boyer 《Foundations of Physics》2012,42(5):595-614
The analysis of this article is entirely within classical physics. Any attempt to describe nature within classical physics
requires the presence of Lorentz-invariant classical electromagnetic zero-point radiation so as to account for the Casimir
forces between parallel conducting plates at low temperatures. Furthermore, conformal symmetry carries solutions of Maxwell’s
equations into solutions. In an inertial frame, conformal symmetry leaves zero-point radiation invariant and does not connect
it to non-zero-temperature; time-dilating conformal transformations carry the Lorentz-invariant zero-point radiation spectrum
into zero-point radiation and carry the thermal radiation spectrum at non-zero temperature into thermal radiation at a different
non-zero temperature. However, in a non-inertial frame, a time-dilating conformal transformation carries classical zero-point
radiation into thermal radiation at a finite non-zero-temperature. By taking the no-acceleration limit, one can obtain the
Planck radiation spectrum for blackbody radiation in an inertial frame from the thermal radiation spectrum in an accelerating
frame. Here this connection between zero-point radiation and thermal radiation is illustrated for a scalar radiation field
in a Rindler frame undergoing relativistic uniform proper acceleration through flat spacetime in two spacetime dimensions.
The analysis indicates that the Planck radiation spectrum for thermal radiation follows from zero-point radiation and the
structure of relativistic spacetime in classical physics. 相似文献
3.
Renal Clearable Luminescent WSe2 for Radioprotection of Nontargeted Tissues during Radiotherapy
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Haixia Liu Junying Wang Yaqi Jing Jiang Yang Xueting Bai Xiaoyu Mu Fujuan Xu Xuhui Xue Lingfang Liu Yuan‐Ming Sun Qiang Liu Haitao Dai Changlong Liu Xiao‐Dong Zhang 《Particle & Particle Systems Characterization》2017,34(6)
High‐energy ionizing radiation is widely used in medical diagnosis and cancer radiation therapy. However, high‐energy radiation can also impose significant damages in healthy tissues during medical treatments via direct DNA damages and indirect damages from production of reactive oxygen species (ROS). Therefore, it is urgent to develop highly effective radioprotectants with low toxicities that can meet the increasing needs for alleviating the adverse effects from cancer radiation therapy and nuclear emergency. In this work, strongly catalytic ultrasmall (sub‐5 nm) cysteine‐protected WSe2 dots are employed to protect healthy tissues against radiation via diminishing radiation‐induced free radicals. The WSe2 dots with high surface activities can recover radiation‐induced DNA damages and eliminate the excessive ROS generated from radiation. In vivo experiments confirm that the survival rate of mice treated with WSe2 dots is significantly elevated with radiation damages postponed under exposure to high‐dose ionizing radiation. Furthermore, the free radicals in major organs and hematological system can be appreciably omitted, suggesting their unique role as free radical scavengers. These WSe2 dots in ultrasmall size show rapid renal clearance of ≈74% injection dose via urine excretion in 24 h and do not cause any apparent toxicity in vivo for up to 30 d. 相似文献
4.
D. V. Karlovets 《Journal of Experimental and Theoretical Physics》2011,113(1):27-45
Polarization radiation generated when a point charge moves uniformly along a straight line in vacuum in the vicinity of media
with a finite permittivity ɛ(ω) = ɛ′ + iɛ″ and sharp boundaries is considered. A method is developed in which polarization radiation is represented as the field of
the current induced in the substance by the field of the moving charge. The solution to the problem of radiation induced when
a charge moves along the axis of a cylindrical vacuum channel in a thin screen with a finite radius and a finite permittivity
is obtained. Depending on the parameters of the problem, this solution describes various types of radiation (Cherenkov, transition,
and diffraction radiation). In particular, when the channel radius tends to zero and the outer radius of the screen tends
to infinity, the expression derived for the emitted energy coincides with the known solution for transition radiation in a
plate. In another particular case of ideal conductivity (ɛ″ → ∞), the relevant formula coincides with the known results for
diffraction radiation from a circular aperture in an infinitely thin screen. The solution is obtained to the problem of radiation
generated when the charge flies near a thin rectangular screen with a finite permittivity. This solution describes the diffraction
and Cherenkov mechanisms of radiation and takes into account possible multiple re-reflections of radiation in the screen.
The solution to the problem of radiation generated when a particles flies near a thin grating consisting of a finite number
of strips having a rectangular cross section and a finite permittivity and separated by vacuum gaps (Smith-Purcell radiation)
is also obtained. In the special case of ideal conductivity, the expression derived for the emitted energy coincides with
the known result in the model of surface currents. 相似文献
5.
O. N. Tchaikovskaya E. A. Karetnikova I. V. Sokolova T. V. Sokolova E. S. Fedorova N. S. Kudryasheva 《Russian Physics Journal》2008,51(12):1344-1355
Fluorescent characteristics of the photo- and biotransformations of 2-methylphenol, 4-methylphenol and their mixtures in water
exposed to uv radiation of various sources and to Penicillium tardum H-2 culture have been studied. The toxicity of these
solutions has also been investigated by means of bioluminescent testing. Preliminary exposure of a 4-methylphenol solution
(10−3 M) to uv radiation with λ ∼ 308 nm or to the radiation of a mercury lamp inhibited the subsequent microbiological degradation.
Efficient decomposition of methylphenol molecules in the mixture was detected when it was exposed to the radiation of a mercury
lamp or to 222-nm radiation and then subject to biodecomposition. The irradiation of solutions of 2-methylphenol and 4-methylphenol
and their low-concentration mixtures with 308-nm uv radiation or with the radiation of a mercury lamp resulted in detoxication
of the solutions. Extreme toxicity was shown by 4-methylphenol solutions on exposure to uv radiation with λ ∼ 222 nm.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 88–98, December, 2008. 相似文献
6.
Cosmic radiation is one of the most important sources of human exposure to natural radiation. Data regarding the level of cosmic radiation in different areas of Pakistan are lacking. The aim of the present study was therefore to estimate the annual outdoor effective doses from cosmic radiation in the Punjab province of Pakistan. The Punjab province is located between geodetic latitudes 28° and 34° N, and longitudes 69° and 75° E. The mean value of the outdoor annual effective dose was found to be 333 μ Sv, which generates a radiation dose of 0.33 mSv y?1 per caput. This is 87% of radiation dose received by the population in the region from terrestrial sources reported elsewhere. The results of this study will contribute to regional as well as world data regarding the exposure of the population to cosmic radiation. 相似文献
7.
本文推导了四边简支矩形板的辐射阻抗表达式, 利用高斯数值积分方法, 计算了其相对辐射阻抗的数值解. 由不同模态下相对辐射阻抗与频率以及不同长宽比对应的相对辐射阻抗与频率的关系可知, 在中低频段, 模态越低, 辐射阻抗越大, 也就意味着辐射声功率和同振质量越大; 对于一定面积和模态的矩形板, r (r=a/b, 长与宽之比)值越接近1, 即越接近正方形, 辐射阻和辐射抗越大. 本文的方法能对其他复杂边界条件下的、无振动解析解的矩形板的辐射阻抗数值量级大小提供一个参考, 也可由计算弯曲振动的阻抗自然地过渡到活塞振动阻抗的计算. 相似文献
8.
The dynamics of the reflectivity at ?? = 0.53 ??m and the IR radiation of silicon in the wavelength range 0.9?C1.2 ??m is studied under the action of nanosecond ruby laser radiation pulses. When radiation energy density W is lower than the threshold of laser-induced melting of the surface of a semiconductor crystal, the major contribution to the IR radiation emitted by this crystal is made by edge photoluminescence. As the melting threshold is exceeded, the nanosecond dynamics of the detected IR radiation changes from photoluminescence to the thermal radiation of the forming Si phase melt with a high reflectivity. The results of pyrometric measurements of the peak melt surface temperature as a function of W obtained at an effective wavelength ?? e = 1.04 ??m of the detected IR radiation agree with the data of analogous measurements performed at ?? e = 0.53 and 0.86 ??m. 相似文献
9.
《Physics letters. A》2020,384(15):126304
A generalized treatment of skew-cosh-Gaussian lasers with skewness parameters n and s is provided for obtaining bifocal terahertz radiation in a realistic plasma having electron-neutral collisions. In order to find and control the focusing of the radiation, a relation is established between the position of the peak of the radiation field and the parameters n and s. The significant role of these parameters in getting bifocal radiation or its conversion to unifocal radiation (or vice-versa) with a proposal for enhanced efficiency of the scheme is discussed in detail for its medical applications. 相似文献
10.
太空辐射尤其是重离子辐射可造成DNA的破坏、细胞死亡、以及一些癌症的发生,是人类深空探索进程中急需克服的难题. 本文通过重离子加速器产生12C6+重离子束对大鼠头部进行一定剂量的辐射,模拟空间重离子辐射对中枢神经系统(CNS)的生物学效应. 采用基于1H NMR的代谢组学方法对辐射大鼠大脑额叶皮质区进行了测定分析,结合数据的统计分析和检验,发现了包括一些重要CNS神经递质在内的代谢物含量发生明显变化. 这些代谢物主要为:牛磺酸、乳酸、谷氨酸、4-氨基丁酸、以及磷酸胆碱等. 结合差异蛋白质组结果分析,包括4-氨基丁酸、谷氨酸、乳酸、牛磺酸等在内的代谢物参与的主要生物途径,如神经递质的合成途径,以及神经递质受体介导的信号途径可能受重离子辐射的负面影响. 这些发现将为进一步阐明重离子辐射效应的分子机制提供有利信息,从而为从生物学途径探寻有效重离子辐射防护措施提供依据. 相似文献
11.
Computed tomography (CT) uses a high dose of radiation to create images of the body. As patients are exposed to radiation during a CT scan, the use of shielding materials becomes essential in CT scanning. This study was focused on the radiation shielding materials used for patients during a CT scan. In this study, sheets were manufactured to shield the eyes and the thyroid, the most sensitive parts of the body, against radiation exposure during a CT scan. These sheets are manufactured using silicone polymers, barium sulfate (BaSO4) and tungsten, with the aim of making these sheets equally or more effective in radiation shielding and more cost-effective than lead sheets. The use of barium sulfate drew more attention than tungsten due to its higher cost-effectiveness. The barium sulfate sheets were coated to form a multigate structure by applying the maximum charge rate during the agitator and subsequent mixing processes and creating multilayered structures on the surface. To measure radiation shielding effectiveness, the radiation dose was measured around both eyes and the thyroid gland using sheets in three different thicknesses (1, 2 and 3 mm). Among the 1 and 2 mm sheets, the Pb sheets exhibited greater effectiveness in radiation shielding around both eyes, but the W sheets were more effective in radiation shielding around the thyroid gland. In the 3 mm sheets, the Pb sheet also attenuated a higher amount of radiation around both eyes while the W sheet was more effective around the thyroid gland. In conclusion, the sheets made from barium sulfate and tungsten proved highly effective in shielding against low-dose radiation in CT scans without causing ill-health effects, unlike lead. 相似文献
12.
Fengshan Liu Gregory J. Smallwood 《Journal of Quantitative Spectroscopy & Radiative Transfer》2011,112(7):1241-1249
The importance of radiation heat loss in laminar and turbulent diffusion flames at normal gravity has been relatively well recognized in recent years. There is currently lack of quantitative understanding on the importance of radiation heat loss in relatively small scale laminar diffusion flames at microgravity. The effects of radiation heat transfer and radiation absorption on the structure and soot formation characteristics of a coflow laminar ethylene/air diffusion flame at normal- and microgravity were numerically investigated. Numerical calculations were conducted using GRI-Mech 3.0 combustion chemistry without the NOx mechanism and complex thermal and transport properties, an acetylene based soot formation model, and a statistical narrow-band correlated-k non-grey gas radiation model. Radiation heat transfer and radiation absorption in the microgravity flame were found to be much more important than their counterparts at normal gravity. It is important to calculate thermal radiation transfer accurately in diffusion flame modelling under microgravity conditions. 相似文献
13.
The spectral characteristics of radiation from atmospheric-pressure gas-discharge plasma in mixtures of cadmium dibromide vapor with gases (Ne, Ar, Kr, Xe, and N2), as well as the temporal characteristics of the voltage and current, have been investigated. A barrier discharge at the repetition frequency of sine voltage pulses up to 140 kHz has been used to create the gas-discharge plasma and excite the components of the working mixture. The discharge radiation has been analyzed in the spectral range 200–900 nm with a high resolution (0.05 nm). In the spectra, we have revealed radiation from exciplex molecules CdBr(B → X) and CdBr(C → X), atomic lines of cadmium and inert gases, and, in mixtures with xenon, radiation of exciplex molecules XeBr(B → X, B → A). The XeBr(B → X) radiation prevailed in the spectra at mixture temperatures up to 200°C. The further increase of the temperature resulted in the prevalence of the CdBr(B → X) radiation. The most intense CdBr(B → X) radiation was observed in mixtures of CdBr2/Xe. When the temperature of the mixture was higher than 250°C, the discharge radiation had a silvery-white color. Regularities in the spectral characteristics of the radiation from the gas-discharge plasma are discussed. The high-frequency atmospheric-pressure barrier discharge in mixtures of cadmium dibromide with gases, excited by sine voltage pulses, can be used in multiwave and broadband excilamps, operating in the UV and visible regions. 相似文献
14.
Ryan G. McClarren R. Paul Drake 《Journal of Quantitative Spectroscopy & Radiative Transfer》2010,111(14):2095-2105
This paper shows that for systems with optically thin, hot layers, such as those that occur in radiating shocks, radiation will flow uphill: radiation will flow from low to high radiation energy density. These are systems in which the angular distribution of the radiation intensity changes rapidly in space, and in which the radiation in some region has a pancaked structure, whose effect on the mean intensity will be much larger than the effect on the scalar radiation pressure. The salient feature of the solution to the radiative transfer equation in these circumstances is that the gradient of the radiation energy density is in the same direction as the radiation flux, i.e. radiation energy is flowing uphill. Such an anti-diffusive flow of energy cannot be captured by a model where the spatial variation of the Eddington factor is not accounted for, as in flux-limited diffusion models or the P1 equations. The qualitative difference between the two models leads to a monotonic mean intensity for the diffusion model whereas the transport mean intensity has a global maximum in the hot layer. Mathematical analysis shows that the discrepancy between the diffusion model and the transport solution is due to an approximation of exponential integrals using a simple exponential. 相似文献
15.
Reduction of sound radiation by using force radiation modes 总被引:1,自引:0,他引:1
The location of a vibration source within a machine is sometimes found to have a significant effect upon its radiated acoustic power. It is known that a simple reduction of vibration cannot always reduce the radiated acoustic power, so that treatments based on analysis of a structure’s vibration modes are not always effective. At the same time, radiation mode analysis is known to be a powerful tool for interpreting sound radiation since those modes are independent of a structure’s surface vibration. However, knowledge of the radiation modes alone cannot be used directly to understand the relationship between vibration source location and acoustic power radiation. In this paper, it is shown that the radiation mode concept can be extended to understand the relationship between acoustic power and driving force distribution by considering the product of the structure’s mobility matrix and the radiation modes: the resulting functions are here defined to be force radiation modes (frad-modes). An example is presented in which the acoustic power radiated by a simply-supported, baffled beam is reduced by using guidance provided by the structure’s force radiation modes. The results demonstrate that the force radiation modes can be used to guide the reduction of radiated acoustic power by changing the driving force location without the need to perform additional calculations or experiments. 相似文献
16.
Stimulated infrared (IR) emission from a condensed dielectric medium under exposure to a giant pulse of a ruby laser is reported.
This effect was predicted in the theoretical paper [1]. Experimental studies were carried out for a number of molecular liquids
in two experimental geometries. In the first case (“in transmission” geometry) the propagation direction of the detected IR
radiation coincided with that of the exciting radiation. In the second case IR radiation generated was detected in the opposite
direction. The angle of divergence of IR radiation was found to be of 10−2 rad, while the conversion efficiency with respect to the pumping intensity depended on the type of molecular liquid and varied
in the range of 0.05–0.6%. Possible microscopic mechanisms of generation of IR radiation under pumping of the dielectric medium
with visible or ultraviolet (UV) radiation are analyzed. 相似文献
17.
M. M. Mogilevsky T. V. Romantsova J. Hanasz T. M. Burinskaya R. Schreiber 《JETP Letters》2008,86(11):709-711
The radiation pattern has been determined on the basis of the comparative analysis of auroral kilometric radiation (AKR) received in the space-diversity mode by two satellites, Interball-2 and Polar. The radiation propagates in a cone with an opening angle ~±25° and the axis aligned with the local magnetic field. The results con-firm the theoretical estimates that the source boundaries play a significant role in the generation of the auroral kilometric radiation and in the formation of the radiation pattern. 相似文献
18.
N. S. Leshenyuk M. V. Prigun G. S. Kruglik N. S. Petrov 《Journal of Applied Spectroscopy》2006,73(2):251-258
Based on analysis of the properties of macromolecules in a coherent optical radiation field and taking into account experimentally
established data on the specificity of the interaction between laser radiation and biomolecules (the dependence of the efficacy
of the interaction on the coherence length, the presence of an effect in a region of the spectrum far away from the absorption
band), we propose a mechanism for wave interaction of coherent optical radiation with macromolecules, and we construct a very
simple mathematical model for such interaction. Using the mathematical model, we calculate the dependence of the vibrational
energy of the macromolecule in a coherent radiation field on the coherence time and the intramolecular relaxation rate. We
show that the increase in the vibrational energy of the macromolecules strongly depends on the radiation coherence length.
When exposed to incoherent radiation, the vibrational energy of the biomolecules remains practically constant, while when
exposed to laser radiation (coherence length ≈3 cm), the vibrational energy of the atoms increases by 2–4 orders of magnitude,
leading to a change in the conformation of the biomolecules and the activity of enzymes.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 225–231, March–April, 2006. 相似文献
19.
基于电荷控制原理建立了辐射感生AlmGa1-mN势垒层应力弛豫对AlmGa1-mN/GaN HEMTs器件电学特性影响的解析模型,并进行了仿真分析.结果表明,对于高Al组分HEMTs器件,AlmGa1-mN势垒层中辐射感生的应力弛豫影响更为显著.辐射感生应力弛豫不但导致2DEG下降和阈值电压正向漂移,而且能够引起漏极输出电流的明显下降.辐射感生应力弛豫是赝配AlmGa1-mN/GaN HEMTs辐射损伤的重要机理之一.
关键词:
mGa1-mN/GaN')" href="#">AlmGa1-mN/GaN
HEMT
辐射损伤
应力弛豫 相似文献
20.
在100TW掺钛蓝宝石飞秒激光器上利用光学CCD相机和光学多道分析仪,分别在靶背法线方向测量了超热电子光辐射的空间分布和光谱.测量结果显示:光辐射空间分布图案呈圆环状,而辐射区域有发散角和光强分布,且包含多种辐射成分.光辐射光谱在800nm附近出现尖峰,是激光的基频(ω0)波,这一现象归因于超热电子束在输运的过程中产生的微束团而引起的相干渡越辐射(CTR).随着激光能量的增加,CTR光谱峰向红光方向移动,基频波红移的主要原因是由于等离子体临界面的迅速膨胀.如果考虑超热电
关键词:
超热电子
光辐射
共振吸收
红移 相似文献