Atom probe tomography (APT) of carbonate minerals

Atom probe tomography (APT) combines the highest spatial resolution with chemical data at atomic scale for the analysis of materials. For geological specimens, the process of field evaporation and molecular ion formation and interpretation is not yet entirely understood. The objective of this study is to determine the best conditions for the preparation and analysis by APT of carbonate minerals, of great importance in the interpretation of geological processes, focusing on the bulk chemical composition. Results show that the complexity of the mass spectrum is different for calcite and dolomite and relates to dissimilarities in crystalochemical parameters. In addition, APT bulk chemistry of calcite closely matches the expected stoichiometry but fails to provide accurate atomic percentages for elements in dolomite under the experimental conditions evaluated in this work. For both calcite and dolomite, APT underestimates the amount of oxygen based on their chemical formula, whereas it is able to detect small percentages of elemental substitutions in crystal lattices. Overall, our results demonstrate that APT of carbonate minerals is possible, but further optimization of the experimental parameters are required to improve the use of atom probe tomography for the correct interpretation of mineral geochemistry.     

自由空间光通信APT系统仿真

高精度、宽带宽的激光捕获、对准和跟踪(APT)技术是自由空间激光通信的关键技术。简要的分析了APT系统的工作原理,建立了仿真的数学模型,利用Simulink语言,实现了卫星激光通信中APT过程的动态仿真,在此基础上设计了星际激光通信复合轴APT综合模拟实验系统。由该系统得出的有效抑制带宽为200～300Hz,经过粗、精两环抑制后的振动残差为1.2μrad,通过实验获得的数据与理论分析一致。仿真结果为系统的设计以及系统的可靠性提供了保证,为进一步发展空间激光通信技术提供了理论依据。     

机载光通信复合轴光路优化设计和跟瞄技术研究

根据机载激光通信的环境和链路距离,采用光电粗精复合轴结构,提出一种双探测器、双光轴机载激光通信复合轴捕获跟踪瞄准系统方案.对整个系统的光路结构进行了分析和优化设计,使粗跟踪精度达120μrad,精跟踪系统带宽大于300Hz,执行动态范围达5mrad,跟踪精度达3μrad,并成功实现通信距离17.5km、通信速率1.5Gbps,误码率达1E-7的飞机对地面激光通信实验.     

多晶硅片反应离子刻蚀制绒后扩散工艺的匹配性

根据机载激光通信的环境和链路距离,采用光电粗精复合轴结构,提出一种双探测器、双光轴机载激光通信复合轴捕获跟踪瞄准系统方案.对整个系统的光路结构进行了分析和优化设计,使粗跟踪精度达120 μrad,精跟踪系统带宽大于300 Hz,执行动态范围达5 mrad,跟踪精度达3 μrad,并成功实现通信距离17.5 km、通信速率1.5 Gbps,误码率达1E-7的飞机对地面激光通信实验.     

空间光通信APT技术中CCD多次采样的分析与研究

利用CCD器件进行光学检测，普遍采用二值化的脉冲计数法，即每个脉冲都代表了一个像元间距，所以CCD的检测分辨率只能达到像元间距的大小。虽然在光学系统中可以采用增加系统放大倍数的方法来提高CCD的检测分辨率，但是由于成像系统的像差、球差以及衍射效应的存在，光学系统最多只能放大几十倍，因此CCD的检测分辨率只能达到微米量级。为进一步提高CCD的检测分辨率，本文提出了一种全新的方法，即多次采样处理，以此将CCD的分辨率提高到亚像元的精度。经过分析论证以及软件的仿真模拟，证实了该方法的可行性。     

Electrical and structural modifications of TZP

The stability range of the metastable tetragonal phase in the ZrO₂-Y₂O₃-TiO₂ and ZrO₂-Y₂O₃-Fe₂O₃ systems was investigated by XRD at room temperature. The solid solubility limit of TiO₂ was found to be as high as 20 mol%, while that of Fe₂O₃ does not exceed 0.8 mol%. Impedance measurements show a decrease of the total conductivity, bulk conductivity and grain boundary conductivity as a result of the TiO₂ and Fe₂O₃ addition. Dc-polarization measurements using the Hebb-Wagner technique were applied to determine the partial hole and electron conductivities of TiO₂ and Fe₂O₃ co-doped samples. These show a slightly higher hole conductivity as compared to pure TZP and a remarkably higher electron conductivity as compared to TiO₂ or Fe₂O₃ doped samples. The Hebb-Wagner curves are interpreted according to a model which considers the addition of mixed valence ions. The influence of the minority charge carriers on the charge-transfer resistance is investigated. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 23–19, 1997.     

Measurement of APT using a combined CERT-AREX approach with varying duty cycles

The goal is to develop an imaging method where contrast reflects amide-water magnetization exchange, with minimal signal contributions from other sources. Conventional chemical exchange saturation transfer (CEST) imaging of amides (often called amide proton transfer, or APT, and quantified by the metric MTR_asym) is confounded by several factors unrelated to amides, such as aliphatic protons, water relaxation, and macromolecular magnetization transfer. In this work, we examined the effects of combining our previous chemical exchange rotation (CERT) approach with the non-linear AREX method while using different duty cycles (DC) for the label and reference scans. The dependencies of this approach, named AREX_double,vdc, on tissue parameters, including T₁, T₂, semi-solid component concentration (f_m), relayed nuclear Overhauser enhancement (rNOE), and nearby amines, were studied through numerical simulations and control sample experiments at 9.4 T and 1 μT irradiation. Simulations and experiments show that AREX_double,vdc is sensitive to amide-water exchange effects, but is relatively insensitive to T₁, T₂, f_m, nearby amine, and distant aliphatic protons, while the conventional metric MTR_asym, as well as several other APT imaging methods, are significantly affected by at least some of these confounding factors.     

Nearest neighbour diagnostic statistics on the accuracy of APT solute cluster characterisation

Diagnostic statistics and information theory techniques have been developed to investigate the accuracy to which solute clusters characterised in atom probe tomography (APT) data can reflect the true nature of the physical clusters in the original specimen. Simulated atom-probe datasets representing a range of atomic solute clustering within a pseudo-binary alloy upon an fcc aluminium lattice were generated for the study. The effectiveness of partitioning the APT-like simulated data based upon a binary classification defined by a distance threshold d _max upon the kth nearest neighbour distance distribution was investigated. Information theory was also used to optimise the selection of the threshold d _max. Analysis of variation was performed upon a factorial design of data simulations with low and high levels of: solute concentration; short-range order; and background to the mass-to-charge-state-ratio spectrum. This meta-analysis showed that the background levels have a significant compromising effect upon the binary classification in low solute systems with relatively low or random levels of clustering. Although the random clustering of higher solute concentrations is better analysed, significantly non-random clustering in both low and high solute concentrations is analysed well despite the presence of high levels of background. A meta-analysis of the binary classification upon a simulated dispersion of coherent precipitates within a similar matrix was also undertaken. Optimal k and d _max parameters are likely a dependent upon the physical dimensions of precipitate size as well as the precipitate/matrix solute concentrations.     

空间光通信APT探测技术中位置敏感器件（PSD）的研究

鉴于空间光通信系统中分辨率在很大程度上影响着整个通信系统的性能，而PSD(position sensitive detector)作为APT(acquisition, pointing and tracking)子系统常用的探测器件，具有分辨率高，无盲区，响应速度较快的优点，分析了PSD的基本结构和定位原理，研究了使用PSD作为空间光通信APT子系统粗跟踪技术的位置分辨率，并指出了提高PSD分辨率的着手点。用实验方案对PSD的分辨率进行了具体的实验分析。通过对实验数据分析可知，PSD的平均位置分辨率达到12.6μm，该值与理论分辨率吻合得较好。这说明PSD作为APT子系统精跟踪探测器的可行性。     

利用“APT”技术鉴别各种31C-H基

本文介绍了用于FT-80A NMR谱仪的EDIT技术的原理、使用方法和主要参数的设置。从实际中总结出APT参数组中的关键参数LT值的设置是:当LT=6,7或8ms时,得到正常APT¹³C谱;当LT=4ms时,CH₃碳信号消失;当LT=2.9或3ms,季碳信号的强度大大增强。这一规律普遍适用(炔类衍生物未做测试)。     

In-medium modifications of hadron properties

The in-medium modifications of hadron properties are briefly discussed. We restrict the discussion to the lattice QCD calculations for the hadron masses, screening masses, decay constants and wave functions. We review the progress made so far and describe how to broaden its horizon.     

Gamma-induced modifications of polycarbonate polymer

Gamma-induced modifications in polycarbonate polymer have been studied in the dose range of 10¹–10⁶ Gy. Thin films of polycarbonate have been irradiated with different gamma doses from a Co⁶⁰ source. To monitor the modifications caused by gamma radiation, FT-IR, differential scanning calorimetry and X-ray diffraction studies have been performed. The studies have indicated that at the dose of 10⁶ Gy, phenolic group forms through scissioning of ester linkage. Though the effect of radiation is most significant at the highest dose, the process of modifications starts at 10³ Gy. Scissioning of the polymeric chain initiates a different morphological zone within the polymer matrix, and the polymer becomes more crystalline with increasing dose. Owing to chain scissioning, the mobility of the polymer increases, which in turn reduces the glass transition temperature of the polymer.     

Holographic control of surface modifications

The application of holographic interferometry to the control of surfaces, such as in processes of electro-deposition, vacuum deposition, and crystal etching is described. As examples, measurements concerning electro-deposition and crystal etching are reported. A double-exposure technique is used and both the thickness of deposited or etched material and the concentration gradient in the electrolyte give rise to interference fringes. From the reconstructed image it is then easy to evaluate the thickness and uniformity of deposition or etching. In the latter case, as is well known, etching figures give useful information about crystal structure and defects.     

Self-oscillations and bunching of striations in ionospheric modifications

Based on the theory of stationary striations created in ionospheric modifications by powerful radio waves, as developed by Gurevich et al. [Phys. Lett. A 206 (1995) 247], the existence of self-oscillations of striations and of a large scale nonlinear structuring in a modified region is predicted. The theory is shown to be in agreement with existing observational data. Direct in situ rocket measurements of the electron temperature inside the striations, analogous to the recent plasma density measurements [M.C. Kelley et al., J. Geophys. Res. 100 (1995) 17 367], are desirable.     

Applicability of the T-matrix method and its modifications

The range of applicability of the T-matrix method and its modifications for solving the problem if the scattering of electromagnetic radiation by nonspherical, axially symmetric particles is investigated analytically and numerically. The use of this method for calculating the characteristics of scattered radiation in the farfield region (the extinction and scattering cross sections, the scattering indicatrix, etc.) is shown to be appropriate for “weak-Rayleigh-type” particles. This condition is met when the intersection of the analytic continuations of the scattered and internal fields contains a ring with the center at the origin of coordinates. For a reliable calculation of the scattered field in the near-field region, it is necessary that a particle be a “Rayleigh-type” one (i.e., the Rayleigh hypothesis be valid for it). In this case, the singularities of the scattered field must occur inside a sphere lying inside a scatterer. Spheroidal particles are weak-Rayleigh-type ones if their semiaxes ratio is $a/b < (\sqrt {2 + 1} )The range of applicability of the T-matrix method and its modifications for solving the problem if the scattering of electromagnetic radiation by nonspherical, axially symmetric particles is investigated analytically and numerically. The use of this method for calculating the characteristics of scattered radiation in the farfield region (the extinction and scattering cross sections, the scattering indicatrix, etc.) is shown to be appropriate for “weak-Rayleigh-type” particles. This condition is met when the intersection of the analytic continuations of the scattered and internal fields contains a ring with the center at the origin of coordinates. For a reliable calculation of the scattered field in the near-field region, it is necessary that a particle be a “Rayleigh-type” one (i.e., the Rayleigh hypothesis be valid for it). In this case, the singularities of the scattered field must occur inside a sphere lying inside a scatterer. Spheroidal particles are weak-Rayleigh-type ones if their semiaxes ratio is , and they are Rayleigh-type ones if . Numerical calculations for spheroids and Chebyshev particles corroborate these conclusions. However, the indicated boundaries are “ spread” (toward the expansion), because the expansion coefficients for the fields are determined with the use of the reduced (i.e., finite) systems. The limiting sizes of the particles for which the T-matrix method gives plausible results are primarily determined by their geometry (shape). __________ Translated from Optika i Spektroskopiya, Vol. 92, No. 5, 2002, pp. 813–825. Original Russian Text Copyright ? 2002 by Farafonov.     

Cold nuclear modifications at RHIC and LHC

We use recent nuclear parton distributions, among them the Hirai — Kumano — Nagai (HKN) and Eskola — Paukkunen — Salgado (EPS08) parameterizations, in our pQCD-improved parton model to calculate the nuclear modification factor, R _AA′ (p _T ), at RHIC and at the LHC. At RHIC, the deuteron-gold nuclear modification factor for pions, measured at p _T ≥ 10 GeV/c in central collisions, appears to deviate more from unity than the model results. The slopes of the calculated R _dAu (p _T ) are similar to the slopes of the PHENIX pion and photon data. At LHC, without final-state effects we see a small enhancement of R _dPb (p _T ) in the transverse momentum range 10 GeV/c ≥ p _T ≥ 100 GeV/c for most parameterizations. The inclusion of final-state energy loss will reduce the R _dPb (p _T ) values.     

Classification of structural modifications of carbon

New schemes have been proposed for the structural classification of carbon phases and nanostructures. These schemes are based on the types of chemical bonds formed in materials and on the number of nearest neighbors with which each atom forms covalent bonds. The classification schemes allow one to describe the already known phases and form the methodological basis for the prediction of new phases and nanostructures.     

Octupole modifications of the Clausius-Mossotti relation

Numerical results are presented for the octupole polarizxability of closed p- and d-shell ions. The polarizabilities are used to determine the alterations form the dipole-octupole coupling to the Clausius-Mossotti relation for the dielectric function of ionic solids. Significant changes in the local field at the alkali atom site are found in the alkali-halides.