The speed of light is an important physical parameter. Currently it is a common belief of the constance of the speed of light regardless of the relative velocity between the source and the observer. Because the speed of light is very fast, if the relative velocity is small compared with the speed of light, it is difficult to detect the effect of the relative velocity on the measurement of the speed of light. In this paper we present a method of comparing the speeds of starlight and the light emitting from a terrestrial source. We use a telescope to collect the light from the star having significant relative velocity with respect to the earth, e.g. Capella. Then we modulate the starlight and the light emitted from the local source into pulses i.e. these pulses leave the modulator simultaneously. After travelling 4.2 km, these pulses are detected by a receiver. If the starlight and the terrestrial light have the same speed, then these pulses must arrive at the receiver at the same time. Our results show that the arrival times of the pulses of starlight are different from that of the local light. For example, the Capella is leaving away from the earth. The Capella pulses arrive later than the local light pulses. It indicates that the speed of Capella starlight is slower than the common believed value, c. The presented method uses one clock and one stick, so the clock synchronization problem and any physical unit transformation can be avoided.
Proc. SPIE. 7981, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2011
KEYWORDS: Signal to noise ratio, Spectrum analysis, Data modeling, Sensors, Interference (communication), Structural health monitoring, Modal analysis, System identification, Stochastic processes, Expectation maximization algorithms
In this study an output-only system identification technique for civil structures under ambient vibrations is carried out,
mainly focused on the Subspace System Identification (SSI) based algorithms. With the aim of finding accurate and true
modal parameters, a stabilization diagram is constructed by plotting the identified poles of the system with increasing the
size of data matrix. Comparative study between different approach, with and without Singular Spectrum Analysis to preprocess
the data, on determining the model order and selecting the true system poles is examined in this study.
Identification task of the real large scale structure: Guangzhou New TV Tower (GNTVT), a benchmark problem for
structural health monitoring of high-rise slender structures is carried out, for which the capacity of SSI-based algorithm
The NB fan is placed in the center of the seismic platform. The commercial DVD pick-up head is used as the sensor to
measure the vibration of the NB fan. We use the automatic positioning program to control the micro stage, and let the
DVD displacement sensor to position the zero-point of S-curve automatically. Experimental results indicate that the
standard deviation is less than 5%, which indicates that the displacement senor has an excellent stabilization.
Furthermore, the commercial DVD pick-up head is used as the sensor, so this system not only reduces the cost but also
obtains good vibration measurement results.
This study aims at inventing a low-price but high-precision 3D touch trigger probe (or a CMM probe). The tip ball of the
stylus, with a diameter smaller than 100 μm, is made by a micro electro discharge machine and wire electro discharge
grinding. The stylus is mounted at the centre of a stiff cross-form frame, which in turn is suspended on four micro beams.
As proven by several experiments, this structure restricts the degrees of freedom on three directions. The displacement
sensor and 2D angle sensor is performed using modified commercial DVD pickup heads to measure the three degrees of
motional freedom on the suspension structure. As for application, since the tip ball is difficult to identify by naked eye,
we use modified commercial webcam and microscope to create a micro imaging system. This imaging system has been
tested to have 2.8mmx2.1mm field of view, and 1.5mm depth of field.
Frequency-domain optical coherence tomography (FD-OCT) has the advantages of an improved sensitivity and a reduced acquisition time since it enables cross-sectional images of the sample of interest to be obtained using a broadband source or a swept source. The phase-shifting method can always be applied to reduce the additional noise within FD-OCT and provide accurate signal processing. We present a phase-shifting method in which a parallel diffraction grating pair is inserted into the reference arm of the OCT system. The gratings separate the spectrum of the illuminating light and stretch the optical pulse in time thereby producing a linear group delay between the adjacent wavelengths in the superluminescent diode light source. The simulation results show that the proposed group-delay-based phase-shifting method improves the precision of the sample parameters extracted using the FD-OCT procedure compared to those obtained using traditional techniques such as the 0/4 phase-shifting method.