521 research outputs found
Sampling expansions associated with quaternion difference equations
Starting with a quaternion difference equation with boundary conditions, a
parameterized sequence which is complete in finite dimensional quaternion
Hilbert space is derived. By employing the parameterized sequence as the kernel
of discrete transform, we form a quaternion function space whose elements have
sampling expansions. Moreover, through formulating boundary-value problems, we
make a connection between a class of tridiagonal quaternion matrices and
polynomials with quaternion coefficients. We show that for a tridiagonal
symmetric quaternion matrix, one can always associate a quaternion
characteristic polynomial whose roots are eigenvalues of the matrix. Several
examples are given to illustrate the results
Floquet multipliers and the stability of periodic linear differential equations: a unified algorithm and its computer realization
Floquet multipliers (characteristic multipliers) play significant role in the
stability of the periodic equations. Based on the iterative method, we provide
a unified algorithm to compute the Floquet multipliers (characteristic
multipliers) and determine the stability of the periodic linear differential
equations on time scales unifying discrete, continuous, and hybrid dynamics.
Our approach is based on calculating the value of A and B (see Theorem 3.1),
which are the sum and product of all Floquet multipliers (characteristic
multipliers) of the system, respectively. We obtain an explicit expression of A
(see Theorem 4.1) by the method of variation and approximation theory and an
explicit expression of B by Liouville's formula. Furthermore, a computer
program is designed to realize our algorithm. Specifically, you can determine
the stability of a second order periodic linear system, whether they are
discrete, continuous or hybrid, as long as you enter the program codes
associated with the parameters of the equation. In fact, few literatures have
dealt with the algorithm to compute the Floquet multipliers, not mention to
design the program for its computer realization. Our algorithm gives the
explicit expressions of all Floquet multipliers and our computer program is
based on the approximations of these explicit expressions. In particular, on an
arbitrary discrete periodic time scale, we can do a finite number of
calculations to get the explicit value of Floquet multipliers (see Theorem
4.2). Therefore, for any discrete periodic system, we can accurately determine
the stability of the system even without computer! Finally, in Section 6,
several examples are presented to illustrate the effectiveness of our
algorithm
Flame Boundary Measurement Using an Electrostatic Sensor Array
Flame boundary is an important geometrical characteristic for the evaluation of flame properties such as heat release rate and radiation. Reliable and accurate measurement of flame boundary is desirable for the prediction of flame structure and the optimization of combustion systems. Such measurement will inform the designers and operators of the combustion systems. This paper presents for the first time a study of using an electrostatic sensor array for flame boundary measurement. The electrostatic sensor is placed in the vicinity of the flame to sense its movement through charge transfer. The principle, design, implementation and assessment of a measurement system based on this methodology are introduced. Comparative experimental investigations with a digital camera conducted on a laboratory-scale combustion test rig show that the electrostatic sensor can respond to the variation of the distance between the electrode and the flame boundary. Reconstruction of the flame boundary is achieved using a set of distance measurements obtained from a sensor array. For diffusion flames over the range of fuel flow rate 0.60-0.80 L/min and premixed flames over the range of equivalence ratio 1.27-3.81, experimental results show that the measurement system is capable of providing reliable measurement of the flame boundary. The correlation coefficients under all test conditions are mostly larger than 0.96, the mean relative errors within 7.4% and the relative root mean square errors within 0.09. More accurate flame boundary measurements are achieved for diffusion flames. In addition, the overall polarity of charges in a flame can be determined from the polarity of the sensor signal
Training Deeper Neural Machine Translation Models with Transparent Attention
While current state-of-the-art NMT models, such as RNN seq2seq and
Transformers, possess a large number of parameters, they are still shallow in
comparison to convolutional models used for both text and vision applications.
In this work we attempt to train significantly (2-3x) deeper Transformer and
Bi-RNN encoders for machine translation. We propose a simple modification to
the attention mechanism that eases the optimization of deeper models, and
results in consistent gains of 0.7-1.1 BLEU on the benchmark WMT'14
English-German and WMT'15 Czech-English tasks for both architectures.Comment: To appear in EMNLP 201
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