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81.
Fethi Jarray 《4OR: A Quarterly Journal of Operations Research》2005,3(4):337-340
This is a summary of the most important results presented in the author's PhD thesis. This thesis, written in French, was
defended on 24 November 2004 and supervised by Marie-Christine Costa and Christophe Picouleau. This thesis consists in developing
the study of discrete tomography problems. It aims at reconstructing discrete objects (matrices, images, discrete sets, etc)
that are accessible only through few projections. A copy of the thesis is available on "http: //cedric.cnam.fr/AfficheArticle.php?id
= 698".
Received: April 2005
AMS classification:
90B70, 68Q17, 52C15, 05B50 相似文献
82.
83.
In this note, we consider a finite set X and maps
W from the set $ \mathcal{S}_{2|2} (X) $ of all 2, 2-
splits of X into $ \mathbb{R}_{\geq 0} $. We show that such a map
W is induced, in a canonical way, by a binary
X-tree for which a positive length $ \mathcal{l} (e) $ is
associated to every inner edge e if and only if (i) exactly
two of the three numbers W(ab|cd),W(ac|bd), and
W(ad|cb) vanish, for any four distinct elements
a, b, c, d in X,
(ii) $ a \neq d \quad\mathrm{and}\quad W (ab|xc) + W(ax|cd) = W(ab|cd) $ holds for all
a, b, c, d, x
in X with
#{a, b, c, x} = #{b, c, d, x} = 4
and $ W(ab|cx),W(ax|cd) $ > 0, and (iii) $ W (ab|uv) \geq \quad \mathrm{min} (W(ab|uw), W(ab|vw)) $
holds for any five distinct elements a, b, u, v, w in
X. Possible generalizations
regarding arbitrary $ \mathbb{R} $-trees and applications regarding tree-reconstruction algorithms
are indicated.AMS Subject Classification: 05C05, 92D15, 92B05. 相似文献
84.
光声成像结合了光学成像和声学成像的优点,是一种高分辨率,高对比度的无损伤医学成像技术.一种改进的同步迭代算法应用于光声图像重建.仿真和模拟结果表明,与传统的代数迭代算法相比,在90°,135°,180°的有限场光声成像中,此算法对测量误差的校正和迭代次数的收敛上具有较大的优势,图像重建的速度和成像质量都有了明显的提高.实验中,一种圆形扫描结构的光声成像装置,用于180°的有限场扫描,利用改进的同步迭代算法,重建出了高对比度和高分辨率(60μm)的鸡胚胎光声血管图像.实验证明,这种算法的应用,大幅度减少了数据采集时间,为光声成像技术运用于实时监测血流灌注和肿瘤光动力治疗的血管损伤效应提供了潜在的应用价值.
关键词:
光声成像
有限角度
代数迭代算法
光声血管成像 相似文献
85.
基于Hilbert变换的相空间重建方法在HLS逐束团测量系统中的应用 总被引:1,自引:0,他引:1
引入基于Hilbert变换的相空间重建手段, 对合肥光源(HLS)逐束团测量系统采集的数据进行了全面的分析, 其中包括单个束流位置监测器(BPM)数据的相空间重建, 逐圈逐束团振荡相位信息、束团振荡模式信息、逐束团横向工作点(tune值)变换. 提出了新的分析束团tune值的手段, 提供传统方法无可比拟的更高的时间和频率分辨率. 还对不同模式的阻尼率进行了计算, 这为衡量逐束团反馈系统的效果提供了确实可靠的方法. 相似文献
86.
S.M. Driver 《Surface science》2007,601(2):510-517
We have used a novel fibre-optic low-energy electron diffraction (FO-LEED) instrument, capable of low flux measurements that minimise electron beam damage to surface overlayers, to study methanethiolate (CH3-S-) structural phases formed on Cu{1 1 1} at temperatures between 110 and 300 K. Three structural phases were seen: a (√3 × √3)R30° phase that forms at 110-140 K; a (4 × 4) phase which was observed transiently at 110 K; and a pseudo-{1 0 0} reconstructed phase which forms at room temperature. We discuss these in the context of previous studies of this system, and demonstrate the ability of the FO-LEED instrument to record high-quality LEED patterns and intensity data from a strongly beam-sensitive surface. 相似文献
87.
Several surface analysis techniques were combined to study the initial stages of oxidation of Cu(1 1 1) surfaces exposed to O2 at low pressure (<5 × 10−6 mbar) and room temperature. Scanning tunneling microscopy (STM) results show that the reactivity is governed by the restructuring of the Cu(1 1 1) surface. On the terraces, oxygen dissociative adsorption leads to the formation of isolated O adatoms and clusters weakly bound to the surface. The O adatoms are located in the fcc threefold hollow sites of the unrestructured terraces. Friedel oscillations with an amplitude lower than 5 pm have been measured around the adatoms. At step edges, surface restructuring is initiated and leads to the nucleation and growth of a two-dimensional disordered layer of oxide precursor. The electronic structure of this oxide layer is characterised by a band gap measured by scanning tunneling spectroscopy to be ∼1.5 eV wide. The growth of the oxide islands progresses by consumption of the upper metal terraces to form triangular indents. The extraction of the Cu atoms at this interface generates a preferential orientation of the interface along the close-packed directions of the metal. A second growth front corresponds to the step edges of the oxide islands and progresses above the lower metal terraces. This is where the excess Cu atoms extracted at the first growth front are incorporated. STM shows that the growing disordered oxide layer consists of units of hexagonal structure with a first nearest neighbour distance characteristic of a relaxed Cu-Cu distance (∼0.3 nm), consistent with local Cu2O(1 1 1)-like elements. Exposure at 300 °C is necessary to form an ordered two-dimensional layer of oxide precursor. It forms the so-called “29” superstructure assigned to a periodic distorted Cu2O(1 1 1)-like structure. 相似文献
88.
A simple, rigid pair-potential model is applied to investigate the dynamics of the (0 0 0 1) α-Al2O3 and α-Cr2O3 surfaces using the molecular dynamics technique. The simulations employ a two-stage equilibration process: in the first stage the simulation-cell size is determined via the constant-stress ensemble, and in the second stage the equilibration of the size-corrected simulation cell is continued in the canonical ensemble. The thermal expansion coefficients of bulk alumina and chromia are evaluated as a function of temperature. Furthermore, the surface relaxation and mean-square displacement of the atoms versus depth into the slab are calculated, and their behaviour in the surface region analysed in detail. The calculations show that even moderate temperatures (∼400 °C) give rise to displacements of the atoms at the surface which are similar to the lattice mismatch between α-alumina and chromia. This will help in the initial nucleation stage during thin film growth, and thus facilitate the deposition of α-Al2O3 on (0 0 0 1) α-Cr2O3 templates. 相似文献
89.
The morphology and structure of Pt deposited on a WSe2(0 0 0 1) van der Waals surface have been investigated by reflection high energy electron diffraction and scanning tunneling microscopy. At room temperature, the initial growth is characterized by the formation of three-dimensional fcc Pt islands with (1 1 1) orientation. In contrast, at higher temperatures of about 450 °C the formation of a novel chemically ordered Pt-Se alloy is observed. Based on the diffraction patterns, a tetragonal DO22-type structure of a Pt3Se compound is suggested. With increasing Pt thickness, this chemically ordered alloy disappears and an additional superstructure occurs, which is accompanied by the coalescence of the islands. The observed superstructure is attributed to a strong Se diffusion towards the growth surface, forming most likely a PtSe2 alloy with the CdI2-type layered structure on the top surface. Due to the lateral lattice mismatch between the Pt(1 1 1) layers and the PtSe2(1 1 1) top layer, a Moiré pattern with a period of 1.1 nm is created, which might be used as a long-range atomic pattern for further nanostructure growth. 相似文献
90.
Density functional calculations have been used to investigate the (0 0 1) surface of cubic SrZrO3 with both SrO and ZrO2 termination. Surface structure and electronic structure have been obtained. The SrO surface is found to be similar to its counterpart in SrTiO3, while there are marked differences between the ZrO2 and TiO2 terminations in SrZrO3 and SrTiO3, respectively, concerning surface relaxation and rumpling. For the ZrO2-terminated surface of SrZrO3, the covalency of the interaction between the outmost Zr and the O beneath is enhanced as a result of their bond contraction. The band gap reduction and the presence of the surface states are also discussed in relation with the behavior of the electrostatic potential. 相似文献