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101.
102.
医用硬性内窥镜畸变的评定基础和方法 总被引:2,自引:1,他引:2
建立医用硬性内窥镜畸变的评定基础和方法,用视轴对称的球面Z视场为模型来模拟体腔凹面特征,以建立内窥镜物像共轭的分析基础;运用光学原理并结合ISO9039:1994“光学和光学仪器光学系统质量评价———畸变的测定”的定义原则,并根据理论畸变的临床要求确定畸变定义;采用主光线追迹原理推导不同球面Z形状的畸变换算通式。创立了医用硬性内窥镜以单位相对畸变表述的定义和表达式,并导出变换视场面的畸变换算通用公式和测试方法。本文建立的畸变评定基础和方法适用于医用硬性内窥镜的标准应用。 相似文献
103.
半导体桥生成的等离子体由于温度高、尺度小、持续时间短等特点,对其温度的瞬态测量是个难题.本文采用高速数字存贮示波器应用原子发射光谱双谱线法对半导体桥等离子体温度进行了实时瞬态测量,并对在22μF电容下不同充电电压对半导体桥等离子体温度的影响进行了系统的研究,得到了22μF电容下等离子体最高温度与充电电压的关系式Tmax=700.6 115.2U. 相似文献
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A novel local principal component analysis (LPCA) technique is presented for activation signal detection in functional magnetic resonance imaging (fMRI) without explicit knowledge about the shape of the model activation signal. Unlike the traditional PCA methods, our LPCA algorithm is based on a measure of separation between two clusters formed by the signal segments in active periods and inactive periods, which is computed in an eigen-subspace. In addition, we only applied PCA to the temporal sequence of each individual voxel instead of applying PCA to the fMRI data set. In our algorithm, we first applied a linear regression procedure to alleviate the baseline drift artifact. Then, the baseline-corrected temporal signals were partitioned into active and inactive segments according to the paradigm used for the fMRI data acquisition. Principal components were computed from all these segments for each voxel by PCA. By projecting the segments of each voxel onto a linear subspace formed by the corresponding most dominant principal components, two separate clusters were formed from active and inactive segments. An activation measure was defined based on the degree of separation between these two clusters in the projection space. We show experimental results on the activation signal detection from various sets of fMRI data with different types of stimulation by using the proposed LPCA algorithm and the standard t-test method for comparison. Our experiments indicate that the LPCA algorithm in general provides substantial signal-to-noise ratio improvement over the t-test method. 相似文献
106.
Correlations of conserved charges,i.e.,the baryon number,electric charge,and strangeness,are calculated at finite temperature and chemical potentials up to the fourth order.The calculations are done ina 2+1 flavor low energy effective theory,in which the quantum and thermal fluctuations are encoded through the evolution of flow equations within the functional renormalization group approach.Strangeness neutrality and a fixed ratio of the electric charge to the baryon number density are implemented throughout the computation.We find that higher-order correlations incorporate more sensitive critical dynamics than the quadratic ones.In addition,a non-monotonic dependence of the fourth-order correlations between the baryon number and strangeness,i.e.,-χ31BS/χ2Sand χ22BS/χ2S,on the collision energy is also observed. 相似文献
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The synthesis of novel symmetrical liquid crystalline compounds based on 5-methyl-5-[2-(4-alkyloxyphenyl)-2-hydroxyethyl]-2,2-bipyridines is reported, together with some physical properties. Although the chelating head-groups are connected via a chiral sp3 carbon atom, all the materials are mesomorphic. Intermolecular hydrogen bonding between pyridino and hydroxy fragments in the mesophases is made apparent by FTIR spectroscopy. 相似文献
110.
One series of two-ring and two series of three-ring mesogens with 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10-heptadecafluorodecaoxy terminal chains containing tolane or biphenyl units have been synthesized. Their mesomorphic properties were observed and measured by optical polarizing microscopy and differential scanning calorimetry. The three-ring mesogens only exhibit a wide smectic C phase when the length of their hydrocarbon chains is intermediate. 相似文献