An Experimental Study of a Cooperative Positioning System

Several position identification methods are being used for mobile robots. Dead reckoning is a popular method but due to the error accumulation from wheel slippage, its reliability is low for measurement of long distances especially on uneven surfaces. Another popular method is the landmark method, which estimates current position relative to known landmarks, but the landmark method's limitation is that it cannot be used in an uncharted environment. Thus, this paper proposes a new method called Cooperative Positioning System (CPS) that is able to overcome these shortcomings. The main concept of CPS is to divide the robots into two groups, A and B where group A remains stationary and acts as a landmark while group B moves and then group B stops and acts as a landmark for group A. This process is repeated until the target position is reached. Compared with dead reckoning, CPS has a far lower accumulation of positioning errors, and can also work in three dimensions. Furthermore, CPS employs inherent landmarks and therefore can be used in uncharted environments unlike the landmark method. In this paper, we introduce the basic concept of CPS and its positioning principle. Next, we outline a second prototype CPS machine model (CPS-II) and discuss the method of position estimation using the variance of positioning error and weighted least squares method. Position identification experiments using the CPS-II model give a positioning accuracy of 0.12% for position and 0.32 degree for attitude after the robots traveled a distance of 21.5 m.     

All-optical switching in a distributed-feedback GaInAsP waveguide

The characteristics of all-optical switching in a waveguide device with a distributed-feedback structure were experimentally investigated. The device was composed of a strip-loaded GaInAsP/InP waveguide and a distributed-feedback structure, which was fabricated by a combination of reactive-ion etching and electron-beam exposure. In the experiments, several optical switching operations were demonstrated. In particular, the all-optical set-reset operation and threshold operation were obtained.     

Motional coherency in chain dynamics of polybutadiene studied by molecular dynamics simulations

Molecular dynamics simulations of 1,4-polybutadiene in bulk amorphous state were performed. Results were compared with the recent neutron spin-echo measurements. To investigate motional coherency the relaxation rates for the collective and self-motions, the collective and self-relaxation rates, were evaluated for the short and long time regimes of the normalized intermediate scattering functions. The scattering vector dependence of the collective relaxation rates estimated for both fast and slow processes indicated a minimum at scattering vector q = 1.5 Å⁻¹, corresponding to the position of a peak in the static structure factor. The self-relaxation rates increased monotonously with q. A phenomenon known as de Gennes narrowing was reproduced well in the simulation and found to be originated from the inter-molecular correlation. The collective relaxation rate evaluated for fast process appeared to modulate around a peak of q = 2.9 Å⁻¹, corresponding to the intra-molecular correlation.     

Study on anisotropy of growth rate of ice crystal in supercooled water

The purpose of this research was to investigate the ice growth of a single crystal in three dimensions. Three-dimensional pattern of ice crystal growth in supercooled water was observed using Mach–Zehnder spectro-interferometer. Temperature was varied from −0.3 to −1.6 °C. It was found that the ice crystal began to grow as a single crystal at the tip of the capillary tube and propagated freely in supercooled water. Time variation of the shape of dendrite on a–c plane was obtained. It was found that half parabola fits the shape very closely, and the coefficient of squared term, a, of a quadratic function was calculated. The coefficient, a varied in time but at quasi steady state it was found to be depending mostly upon the degree of supercooling. Furthermore, the growth velocity in c-axis at the flat surface was calculated from the thickness measured. It was found that the velocity in c-axis is independent of the degree of supercooling but depends upon time, in other words, the thickness in c-axis.     

Type-Based Useless-Variable Elimination

Useless-variable elimination is a transformation that eliminates variables whose values does not affect the result of a computation. We present a type-based method for useless-variable elimination and prove its correctness. The algorithm is a surprisingly simple extension of the usual type-reconstruction algorithm. Our method has several attractive features. First, it is simple, so that the proof of the correctness is clear and the method can be easily extended to deal with a polymorphic language. Second, it is efficient: for a simply-typed -calculus, it runs in time almost linear in the size of an input expression. Moreover, our transformation is optimal in a certain sense among those that preserve well-typedness, both for the simply-typed language and for an ML-style polymorphically-typed language.     

Subspace information criterion for model selection

The problem of model selection is considerably important for acquiring higher levels of generalization capability in supervised learning. In this article, we propose a new criterion for model selection, the subspace information criterion (SIC), which is a generalization of Mallows's C(L). It is assumed that the learning target function belongs to a specified functional Hilbert space and the generalization error is defined as the Hilbert space squared norm of the difference between the learning result function and target function. SIC gives an unbiased estimate of the generalization error so defined. SIC assumes the availability of an unbiased estimate of the target function and the noise covariance matrix, which are generally unknown. A practical calculation method of SIC for least-mean-squares learning is provided under the assumption that the dimension of the Hilbert space is less than the number of training examples. Finally, computer simulations in two examples show that SIC works well even when the number of training examples is small.     

Temperature Dependence of the Velocity of Sound in Liquid Metals of Group XIV

The temperature dependences of the velocity of sound in liquid Pb, Sn, Ge, and Si have been measured by means of the pulse transmission technique over temperature ranges of 610–1078 K, 608–1463 K, 1215–1443 K, and 1723–1888 K, respectively. In both liquid Pb and Sn, the velocities of sound decrease linearly with increasing temperature, which is the same temperature dependence as shown in many other liquid metals. On the other hand, the velocities of sound in liquid Ge and Si exhibit anomalous temperature dependences. In Ge, the velocity of sound has a distinct maximum around 1280 K and decreases linearly at higher temperatures. In Si, the velocity of sound increases monotonically with increasing temperature in the temperature range investigated. It is considered that these results predict that the coordination numbers of liquid Ge and Si increase with increasing temperature.     

Sliding window protocol with selective-repeat ARQ: performance modeling and analysis

A sliding window mechanism is well known to be a convenient way to integrate cumulative acknowledgement and flow control functions in a simple manner. Hence, widely used reliable data-transfer protocols such as TCP-SACK and RLC utilize this sliding window mechanism in conjunction with a selective-repeat ARQ (automatic repeat request) function, namely, the selective-repeat sliding window protocol (SR-SWP). We demonstrate that SR-SWP yields a throughput restraint effect (TORE) in particular situations when packet losses occur. We propose an analytical performance model to represent the TORE in the case of heavy traffic. Using this model, we derive explicit forms of goodput and mean resequencing delay, which are fundamental qualities of service parameters. From numerical results, we demonstrate that the impact of TORE on the performance is not negligible for high packet-loss probabilities. Furthermore, we show that the SR-SWP model exhibits the lower goodput and the smaller mean resequencing delay than those obtained from the traditional SR-ARQ protocol model.     

Transverse surface waves on a piezoelectric material carrying a functionally graded layer of finite thickness

The propagation behavior of transverse surface waves (Love waves) in a piezoelectric half space of polarized ceramics carrying a functionally graded material layer is studied from the three-dimensional equations of linear piezoelectricity. The Wentzel–Kramers–Brillouin (WKB) asymptotic technique is adopted for the theoretical derivations of analytical solutions in the functionally graded layer. The dispersion relations of Love wave in the structure are obtained for both electrically open and shorted cases. Firstly, these solutions are used to study effect of the gradient coefficients on the dispersive relations and phase velocities of Love wave propagation. Then influence of the gradient coefficients on the electromechanical coupling factor is discussed in detail. The results reported are meaningful for the design of surface acoustic wave (SAW) devices with high performance.