基于信号强度的改进型井下测距算法的研究

针对现有信号强度测距法计算误差较大的问题，研究射频天线性能参数对电磁波传输的影响，提出将天线阻抗特性与能量接收相联系，将水平极化衰减率应用于求解天线回路上任意微分长度元的电磁波功率密度，从而建立了符合井下射频天线特性的信号能量与传输距离的关系式，推导出求解井下基站与目标之间距离的改进型信号强度测距法。选取相同的巷道环境验证了算法改进前后对目标的定位能力，结果表明经过改进后算法得出的目标位置与改进前相比更加准确，定位误差缩小6.9 m2，且改进后算法与改进前相比大幅减少全巷道内基站的布设数量，提高了基站的利用率，充分证明提出的改进型信号强度测距法更加适合井下巷道中的目标测距及定位，计算结果更加准确可靠。     

Absence of a self-induced decay effect in Au

We report the results of an improved experiment aimed at determining whether the half-life (T_1/2) of ¹⁹⁸Au depends on the shape of the source. In this experiment, the half-lives of a gold sphere and a thin gold wire were measured after each had been irradiated in the NIST Center for Neutron Research. In comparison to an earlier version of this experiment, both the specific activities of the samples and their relative surface/volume ratios have been increased, leading to an improved test for the hypothesized self-induced decay (SID) effect. We find T_1/2(sphere)/T_1/2(wire)=(0.9993±0.0002), which is compatible with no SID effect.     

Decay Heat Calculations Based on Theoretical Estimation of Average Beta- and Gamma-Energies Released from Short-Lived Fission Products

Fission product decay heat of ²³⁵U was calculated for short cooling-time on the basis of a preliminary version of a new decay data library recently completed by the Japanese Nuclear Data Committee. It was shown that a full adoption of recent publications of decay schemes to derive average energies of β- and γ-rays, ē_β, and ē_γ, leads to a large underestimation of the γ-ray component of the decay heat and to an overestimation of the β-ray component. In order to remedy this, theoretical values of ē_β and ē_γ were introduced for high Q-value decays, which were obtained with a gross theory of β-decay. It improved remarkably the agreement between calculation and experiment not only for the ²³⁵U decay heat but for ²³⁹Pu and ²⁴¹Pu as well. It was concluded that a large part of decay schemes recently published for high Q-value nuclides are inappropriate to use in calculations of ē_β and ē_γ, because they fail to reproduce the effect of β- strengths at high excitations, which makes ē_β small and ē_γ large. The use of the gross theory introduces this effect correctly into the values of ē_β and ē_γ and, hence, leads to a quite good prediction of both β- and γ-ray components of the decay heat.     

Environmental effects on nuclear decay rates

The possible change of nuclear decay rates in different environments has long been an interesting topic due to its importance not only in nuclear physics but also in astrophysics, geological dating, condensed matter physics, etc. The progress in the inves     

多维非线性sobolev型发展方程(组)的初边值问题

本文主要研究了如下的初边值问题其中Ω∈R~n是一有界开集,其边界Ω充分光滑。进一步证明了这个问题整体解的存在唯一及t→ ∞时解的渐近性质。     

Optical properties of CdSe quantum dots grown on ZnSe and ZnBeSe by molecular beam epitaxy

We report detailed studies of the optical properties of CdSe quantum dots (QDs) grown on ZnSe and ZnBeSe by molecular-beam epitaxy (MBE). We performed steady-state and time-resolved photoluminescence (PL) measurements and observe that nonradiative processes dominate at room temperature (RT) in the CdSe/ZnBeSe QDs structures, though these nonradiative processes do not dominate in the CdSe/ZnSe QDs structures up to RT. We performed secondary ion-mass spectrometry (SIMS) measurement and propose that the oxygen incorporation in the ZnBeSe layers (possibly caused by the reactivity of Be) may contribute to the dominant nonradiative processes at high temperatures in the QDs grown on ZnBeSe.     

羟基磷酸钙ESR信号热衰退中的二级动力学过程

人工合成羟基磷酸钙和牙珐琅化石的等温退火实验表明，它们的ＥＳＲ信号的热衰退系一级和二级动力学过程的混合效应。二级衰退常数强依赖于温度。粗测其值在２８０℃时为１０＾－１９ｇ／ｓ量级。二级过程的存在对ＥＳＲ法测早期古人类遗址动物牙化石年龄的影响需进一步研究。     

Materials decay and environmental attack in the Pio Palace at Carpi: A holistic approach for historical architectural surfaces conservation

Since the XIV century the Pio Palace in Carpi (MO, Italy) has been subjected to many additions and rearrangements and, in the last decades, to wide restoration works. Nevertheless the XVII century main portal has not been restored yet, due to its complex and peculiar surface alteration forms in comparison with the other parts of the building, and still suffers a deep decay and degradation by complex chemical-physical processes.     

Weathering,water absorption,and durability of silicon,acetylated, and heat‐treated wood

In this study, two colloidal dispersions of pure amorphous silicon dioxide particles, acetylated, and heat‐treated samples were tested for a possible application as a wood protection agents. The silicon, acetylated, and heat‐treated samples were exposed to an accelerated weathering experiment, and their dimensional stability was assessed. The weathering experiment comprised cycles of 2 h UV‐light irradiation followed by water spray for 18 min. The surface changes of the weathered samples were characterized by FT‐IR spectroscopy and color measurements. According to results, the silicon treatments showed lower color changes than untreated ones. However, acetylated and heat‐treated samples provided the lowest color changes. The resistance of the silicon, acetylated, and heat‐treated wood to decay was studied by means of brown and white rot fungi in laboratory decay tests. Decay test results revealed that acetylated and heat‐treated wood samples showed better decay resistance against P. placenta and C. versicolor than silicon treatments. Samples modified with silicon were exposed in above ground standard lap‐joint test in Ultuna, Sweden. The dispersions of pure amorphous silicon dioxide impregnated in wood did not significantly influence its hygroscopic and dimensional behavior. However, the silicon treatment reduced the color changes caused by weathering. The silicon impregnated samples showed a weak fungal discoloration similar to that of chromated copper arsenate impregnated controls in above ground standard lap‐joint test. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4506–4513, 2006     

Free Radicals in Wheat Seeds Studied by Electron Spin Resonance

ABSTRACT: We used electron spin resonance (ESR) to investigate free radicals in wheat seeds in air or under vacuum in relation to annealing temperature. Annealing in the 100 to 200 °C range resulted in concentration increases of free radicals in samples. A greater increase was observed for experiments carried out in air than for those under vacuum. Most free radicals occurred in the grain surface layer. The bran contained a concentration of free radicals 100 times greater than that of the white grain portion. The reaction of stable free radicals in bran was also studied during thermal decomposition of dibenzoyl peroxide at high pressure. They reacted with shortlived peroxyl radicals in bran to produce a nonradical product.