Functional MRI using intravascular contrast agents: detrending of the relative cerebrovascular (rCBV) time course

In pharmacological fMRI experiments in animal models, blood pool contrast agents may be used to map cerebral blood volume change as a surrogate for neural activation. When the background signal drift due to contrast agent washout is non-negligible over the duration of the signal changes of interest, time-course detrending is essential for accurate interpretation of the experiment. Detrending approaches based on estimation of the background signal from a baseline period of the time course prior to pharmacological (or functional) challenge were evaluated with the aim of identifying a robust method of estimating the contrast agent washout contribution to the background signal drift. For fMRI studies in the rat, it was found that a constrained fit of a mono-exponential washout model was more accurate than a constant background approximation and unconstrained fits for experiments investigating the functional response to rapid pharmacological challenges such as cocaine and amphetamine. Moreover, the constrained fitting approach allows shorter baseline periods than unconstrained extrapolation, reducing the required duration of the experiment.     

激光大气等离子体时间演化特性的光谱研究

采用延时光谱法和谱线演化法 ,对YAG脉冲激光器 1 0 6 μm光束击穿一个大气压的空气所产生的等离子体进行了时间分辨光谱研究。对激光大气等离子体连续光谱的短波带与长波带分别进行了时间分辨测量 ,结果表明两者的衰变速率均在等离子体激发约 0 5微秒以后明显变慢。分析认为这种衰变速率的变慢可能与空气中氧对自由电子的吸附与去吸附有关。对激光大气等离子体线状光谱所作的时间分辨测量则表明 ,大部分线状光谱的演化寿命大于其标称寿命 ,部分线状光谱还呈现“衰变—增涨—衰变”的复杂形式。分析认为线状光谱的这些演化特征可能与等离子体在衰变期间的各种复合过程和能量转移过程有关。     

合肥光源逐圈束流位置监测系统中的定时系统

 定时系统是合肥光源逐圈束流位置监测和相空间测量系统中的重要组成部分,其主要目的是为数据采集卡提供与环内电子束团同步的时钟信号。该系统包含高速ECL时钟成形、分频电路、程控延时电路、控制模块等部分。可实现延时范围0～220ns,最小延时步距0.5ns,调整精度0.1ns,时钟抖动小于200ps。系统控制软件基于客户/服务器结构,操作灵活、方便。     

Exact multiplicity and ordering properties of positive solutions of a p-Laplacian Dirichlet problem and their applications

We study the exact multiplicity and ordering properties of positive solutions of the p-Laplacian Dirichlet problem

     

ZnSe/SiO2半导体量子点玻璃的光谱特性

对采用溶胶凝胶法制备的ZnSe/SiO2半导体量子点玻璃的光谱性质进行了测试分析.UV-Vis透射光谱中观察到光吸收边相对于体相半导体有明显蓝移.稳态发射光谱(PL)中观察到ZnSe纳米晶体的位于蓝区的基本呈高斯分布的弱的最低激子发射峰、强而宽的表面态发光带以及对应杂质能级的三个锐峰发光.时间分辨荧光光谱(TRPL)中观察到发光效率高的最低激子发射峰,并测量其荧光衰减寿命,经尾部拟合为28.5 ps.同时,结合有效质量近似(EMA)模型,估计ZnSe纳米晶体的平均粒径介于2.45~3.60 nm之间,尺寸分布基本呈高斯型.     

A data-analysis method for identifying differential effects of time-delayed feedback forces and periodic driving forces in stochastic systems

In this work a method is developed for analyzing time series of periodically driven stochastic systems involving time-delayed feedback. The proposed data-analysis method yields dynamical models in terms of stochastic delay differential equations. On the basis of these dynamical models differential effects of driving forces and time-delayed feedback forces can be identified.     

An RF quadrupole–time-of-flight system for isobar-separation and multiplexed low-energy Rare-Isotope Beam experiments

A novel system consisting of RF quadrupole and time-of-flight sections is proposed, in which ions can be cooled, bunched, mass separated with a resolution sufficient to differentiate between isobars, and guided to different experimental setups, e.g. for precision mass measurements or mass-resolved decay spectroscopy. It enables multiplexed operation of several connected experiments and interleaved measurements using different nuclides in one connected experiment. Such a system could be employed advantageously at in-flight facilities, at which experiments with stopped exotic nuclei are made possible using gas-filled stopping cells, such as SHIPTRAP at GSI, or potentially at ISOL facilities. First results for individual stages of the system are presented.     

Power-law autocorrelated stochastic processes with long-range cross-correlations

We develop a stochastic process with two coupled variables where the absolute values of each variable exhibit long-range power-law autocorrelations and are also long-range cross-correlated. We investigate how the scaling exponents characterizing power-law autocorrelation and long-range cross-correlation behavior in the absolute values of the generated variables depend on the two parameters in our model. In particular, if the autocorrelation is stronger, the cross-correlation is also stronger. We test the utility of our approach by comparing the autocorrelation and cross-correlation properties of the time series generated by our model with data on daily returns over ten years for two major financial indices, the Dow Jones and the S&P500, and on daily returns of two well-known company stocks, IBM and Microsoft, over five years.     

Generating synthetic time series from Bak-Sneppen co-evolution model mixtures

The Bak-Sneppen model of co-evolution is used to derive synthetic time series with a priori specified fractal dimension (or Hurst exponent) through a mixing of processes in various lattice dimensions. Both theoretical and numerical analyses concern the avalanches at the critical threshold and provide a model for time series reconstruction that can be tested as an alternative to the classical fractional Brownian motion (fBm) because of differences in properties. New results on critical threshold and avalanche structure are obtained up to Euclidean dimension d=6. The method involves a lattice-based structure and therefore is suitable for the application of parallel computing.