基于光纤光栅传感阵列及双目视觉的内窥镜三维显形系统的研究

内窥镜柔性杆在体内的形状显示是一种新型的技术,在这种技术的帮助下,当病人的结肠处于一种不正确的位置上或者说在进境的过程中内窥镜柔性杆的形状形成了扭曲,而形状扭曲会导致内窥镜检查的不安全性,如果预先知道这种状况的发生,就能给诊断带来安全性。本文主要研究了一种基于光纤光栅传感阵列的内窥镜柔性杆的形状及双目视觉的内窥镜镜手柄部分的姿态检测方法,这两种方法的集成构成了整个内窥镜的显形系统。详细的分析包括基于光纤光栅传感器信息的检测原理以及空间曲线重建算法,内窥镜手柄部分相对于世界坐标系的位姿估计。实验结果证明了提出方法的有效性。比较以前的研究,形状重建的精度已经提高到了4.5mm。通过加入内窥镜手柄的位姿检测,整个三维形状显示子系统变得更加有效和更实用化。     

Rate of strong uniform convergence of k-NN density estimates

Let f_n(x) be the univariate k-nearest neighbor (k-NN) density estimate proposed by Loftsgaarden and Quesenberry (1965). By using similar techniques as in Bahadur's representation of sample quantiles (1966), and by the recent results on the oscillation of empirical processes by Stute (1982), we derive the rate of strong uniform convergence of f_n(x) on some suitably chosen interval J_δ. Some comparison with the kernel estimates is given, as well as the choice of the bandwidth sequence relative to the sample size.     

Non-parametric recursive estimates of a probability density function and its derivatives

Recursive estimates of a probability density function (pdf) are known. This paper presents recursive estimates of a derivative of any desired order of a pdf. Let f be a pdf on the real line and p?0 be any desired integer. Based on a random sample of size n from f, estimators f^(p)_n of f^(p), the pth order derivatives of f, are exhibited. These estimators are of the form $\text{n}{}^{\mathrm{?1}}\text{∑n}\text{j=1}\text{δ}{}_{\mathrm{jp}}$, where δ_jp depends only on p and the jth observation in the sample, and hence can be computed recursively as the sample size increases. These estimators are shown to be asymptotically unbiased, mean square consistent and strongly consistent, both at a point and uniformly on the real line. For pointwise properties, the conditions on f^(p) have been weakened with a little stronger assumption on the kernel function.     

On arcs with weighted points

In the present paper we start the study of arcs with weighted points in a finite projective plane, and we get some particular results about the existence or non-existence of these arcs.     

Characterizations of geometric distribution and discrete IFR (DFR) distributions using order statistics

Let X be a discrete random variable the set of possible values (finite or infinite) of which can be arranged as an increasing sequence of real numbers a₁<a₂<a₃<…. In particular, a_i could be equal to i for all i. Let X_1n≦X_2n≦?≦X_nn denote the order statistics in a random sample of size n drawn from the distribution of X, where n is a fixed integer ≧2. Then, we show that for some arbitrary fixed k(2≦k≦n), independence of the event {X_kn=X_1n} and X_1n is equivalent to X being either degenerate or geometric. We also show that the montonicity in i of P{X_kn = X_1n | X_1n = a_i} is equivalent to X having the IFR (DFR) property. Let a_i = i and $\text{G(i) = P(X≧i), i = 1, 2, …}$. We prove that the independence of {X_2n ? X_1n ∈B} and X_1n for all i is equivalent to X being geometric, where B = {m} (B = {m,m+1,…}), provided G(i) = q^i?1, 1≦i≦m+2 (1≦i≦m+1), where 0<q<1.     

Construction of Youden hyperrectangles

Youden hyperrectangles are higher-dimensional generalizations of balanced block designs and generalized Youden designs. This kind of design has been shown to be optimal for the elimination of multi-way heterogeneity. In this paper, patchwork and geometric methods are combined to construct Youden hyperrectangles for many parameter values.     

Three models of OPEC leadership and policy in the aftermath of Iran

Collapse of the Shah's regime has transformed Iran's attitude regarding oil production policy. The nature of OPEC leadership is changing as well. Three models examine the nature of this leadership inside OPEC: (1) the conventional price leadership model, (2) a model emphasizing a concept of egalitarian leadership, and (3) a team model composed of coalitions. The three models establish the limits within which OPEC leadership is exercised. A composite model drawing upon all three sets of results suggests that Saudi Arabia shapes cartel policy not by itself, but through a dominant coalition of states. For most of the period 1969–1978 this coalition has been stable. Following the unsettling changes of 1973, cooptation of Iran into the dominant coalition in 1974 was an important step in achieving a new level of stability. But during the turbulence of regime transformation in Iran, the nature of the governing coalition appears to have changed. One consequence may be that in the future Saudi Arabia will yield more willingly to arguments heard within OPEC on behalf of upwards price pressure, especially in an atmosphere of growing political isolation and overall tight supply.     

Debt management in a small open economy: A theoretical and an empirical study for Belgium

This article analyzes the effects of debt management and its consequence for the control of base money in a small open economy (Belgium). The study compares the effects obtained from a small theoretical model with the results of a larger empirical model.The theoretical model focuses on the financing of government by money operation, on the bond rate, and on the international reserve of the Central Bank.The empirical model is a medium-term one, including the demand and the supply sectors of the economy and permitting simultaneous analysis of real and financial variables.The effects of an endogeneous or exogenous debt management have been studied by numerical simulation of modification in the public expenditure, the world trade, and the discount rate.     

On UMVU estimators and Bhattacharya bounds in exponential distributions

A subfamily of exponential distributions is considered and it is shown that the variance of the UMVU estimator of an estimable function g(θ) having power series expansion is the limit of Bhattacharya bounds.     

On the optimality of a class of minimal covering designs

It is shown that the minimal covering designs for v=6t+5 treatments in blocks of size 3 are optimal w.r.t. a large class of optimality criteria. This class of optimality criteria includes the well-known criteria of A-, D- and E-optimality. It is conjectured that these designs are also optimal w.r.t. other criteria suggested by Takeuchi (1961).