褶合光谱法考察羟自由基清除剂对紫外照射致DNA变异的作用

采用褶合光谱法考察了紫外线UV A ,UV B ,UV C导致的DNA变异 ,并以褶合光谱差谱值的形式量化表达DNA细微突变的程度。DNA受UV A ,UV B ,UV C作用后 ,差谱值依次增大 ,表明变异程度增大 ;添加二甲亚砜、甘露醇等羟自由基清除剂以后 ,在UV A ,UV B ,UV C作用下 ,差谱值有不同程度的降低 ,呈现一定的抑制变异作用。尽管DNA的变异程度有所区别 ,但它们的差谱点分布区域相似 ,提示UV A ,UV B ,UV C导致的DNA变异类型可能相似 ,两种羟自由基清除剂抑制DNA变异的作用机制也可能相似     

Experimental study of the relationships between the spectral emissivity of brass and the temperature in the oxidizing environment

Effect of surface oxidization on the spectral emissivity of brass is studied over the temperature range from 800 to 1070 K at the wavelength of 1.5 μm. The temperature of brass surface is measured by averaging the two R-type platinum–rhodium thermocouples. The radiant energy emitted by the brass surface is received by an InGaAs photodiode detector. Two kinds of relationships between the spectral emissivity and the temperature are investigated in the oxidizing environment at the elevated temperature. One is the variation of spectral emissivity with the heating-duration time at the given temperature. The other is the variation of spectral emissivity with the temperature at the given heating-duration time. The interference effect of radiation coming from the brass surface and coming from the oxidization film is discussed when the oxidation film on the surface is grown. The resonant structures of spectral emissivity are observed during the whole heating period, in particular at the early stage of heating duration. The analytic formula of spectral emissivity versus the temperature is derived at the heating-duration time of 30, 60, 90, 120, 150, 180, 210, 240, 270 and 300 min, respectively. The conclusion is obtained that coefficients of analytic expressions between the spectral emissivity and the temperature are different from each other for the experimental results obtained at the different heating-duration time, though the polynomial functional form is suitable to fit all the measurements obtained in the present work.     

Classical fluids of negative heat capacity

It is shown that new parametersX can be defined such that the heat capacity C_xT(S/T)_x is negative, even when the canonical ensemble [i.e., at fixed T=(U/S)_Y and YX] is stable. This implies an extension of the classical theory of polytropes from ideal gases to general fluids. As examples of negative heat capacity systems we treat blackbody radiation and general gas systems with nonsingular _T. For the case of a simple ideal gas we even exhibit an apparatus which enforces a constraint X(p, V)=const that makes C_x<0. We then show that it is possible to infer the statistical mechanics of canonicallyunstable systems-for which even the traditional heat capacities are negative-by imposing constraints that stabilize the associated noncanonical ensembles. Two explicit models are discussed.     

A broad-band constant beam-width array with four elements

This paper describes in detail an acoustical array structure with fourelements that have cosine directivity function over a certain frequency range.The acoustical axis directions of these elements are orthogonal to each other,sotheir beams cover all bearing angles within 360°.By use of the amplitude bear-ing method,it is easy to detect the bearing of incident acoustic signal.A specialsound reflection foam rubber is designed as a back baffle of the array.It hasbeen shown,in practice,that the constant beam-width has been obtained for amultiple frequency band of the ratio of 8:1.The paper also gives a mathematicalmodel for the array structure.The theoretical values are consistent with themeasured results.     

Radiological safety assessment inside ancient Egyptian tombs in Saqqara

Many archaeological sites in Egypt are unique worldwide, such as ancient tombs and pyramids, because they document fundamental developments in human civilization that took place several thousands of years ago. For this reason, these sites are visited by numerous visitors every year. The present work is devoted to provide a pre-operational radiological baseline needed to quantify occupational radiation exposure at the famous Saqqara region in Cairo, Egypt. A hyperpure Ge detector has been used in the γ-ray spectrometric analysis while the ²²²Rn concentration was measured using a portable radon monitor RTM 1688-2, SARAD. The mean specific activities of ²²⁶Ra, ²³²Th and ⁴⁰K in the samples collected from the interior walls of the Saqqara tombs were determined and found to show average values of 16, 8.5 and 45 Bq kg^?1, respectively. The concentration of radon was measured inside the tombs Serapeum, South tomb and the Zoser Pyramid (fifth level) and an associated average working level of 0.83 WL was obtained. In order to avoid the health hazards associated with the exposure to radon during the long period of work inside these tombs, proposed solutions are introduced.     

X-ray fluorescence intensity distribution in circular specimens

Summary The relative X-ray fluorescence (XRF) intensities for annular source and various annular specimen are measured with a Ge-Li detection system and calculated by the Monte Carlo numerical techniques (MCNT).Kα X-ray intensities of annular specimens with different radii prepared from a pure-molybdenum foil are measured and it is seen that the measured values are in good agreement with the values calculated by MCNT. The variation of the fluorescence intensity due to the collimator radius is also studied. The differences between the MCNT and experimental results are discussed in terms of the possible sources of errors.     

钾原子中由四波,六波混频过程产生的相干辐射

当双光子共振激发钾原子于６Ｓ能级时，由光泵受激辐射，串级受激辐射参与的四波、六波混频以及电离复合的布居过程，产生了位于可见区的诸多相干辐射，文中对混频机制进行了分析和讨论，并对所测得的相干辐射进行了标识。     

Chemisorption of 1,1-dichloroethene on the Si(1 1 1)-7 × 7 surface

Chemisorption of 1,1-dichloroethene (Cl₂CCH₂) to a Si(1 1 1)-7 × 7 surface was studied by means of X-ray photoelectron spectroscopy using synchrotron radiation, recording chlorine 2p and carbon 1s spectra. For carbon 1s, spectral assignment of the chemisorbed species is based on quantum chemical calculations of chemical shifts in model compounds.The results confirm the identity of covalently bonded 1-chlorovinyl (-CClCH₂) and vinylidene (CCH₂) adspecies. Upon chemisorption at room temperature it was found that about one-third of the molecules break one C-Cl bond while about two-thirds of the adsorbates break two C-Cl bonds. We do not, however, find evidence for isomerization of CCH₂ to di-bonded vinylene (-CHCH-).     

Nd:YAG laser synthesis of nanostructural V2O5 from vanadium oxide sols: Morphological and structural characterizations

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.     

用于同步辐射光源的成像板粉末衍射系统

报道了我们研制的一套成像板粉末衍射装置,对其误差来源进行了详细的分析讨论,并与衍射仪进行了比较.该装置的半径为143.3mm,最大测量角度范围不160°，最大角度(2q )偏差小于0.03°,这些性能指标已被实验所证实,完全可应用于粉末衍射全谱的测量.