Multi-function sensing and imaging devices, GPS, communication and computing devices are being ubiquitously
used in field by engineers in civil engineering and emergence response practice. Field engineers, however, still have
difficulty to balance between ever-increasing data collection demand and capacity of real-time data processing
and knowledge sharing. In addition, field engineers usually work collaboratively in a geospatially large area;
however, the existing sensing and computing modalities used in the field are not designed to accommodate this
condition. In this paper, we present a solution framework of collaborative mobile sensing and computing (CMSC)
for civil infrastructure condition assessment, with the Android-based mobile devices as the basic nodes in the
framework with a potential of adding other auxiliary imaging and sensing devices into the network. Difficulties
in mixed C++ and Java code programming that are critical to realize the framework are discussed. With a
few prototypes illustrated in this paper, we envisage that the proposed CMSC framework will enable seamless
integration of sensing, imaging, real-time processing and knowledge discovery in future engineers-centered field
reconnaissances and civil infrastructure condition assessment.
Nondestructive imaging has been a widely used approach for detection of local structural damage in the engineering
community. By combining image analysis methods, quantities describing the type, severity and extent of damage can
be extracted within the spatial domain of images. However, the current practice of structural health monitoring requires a
temporal characterization of structural damage, or some correlation of structural damage with response data. To accomplish
this, one needs to consider the time scale in using any of the nondestructive imaging techniques, which in turn demands
the use of spatial-temporal image analysis. In this paper, we address the temporal occurrence of cracks on the surface
of concrete structural members, and attempt to monitor cracks, including their inception and propagation, using temporal
image data. We assume under some conditions for objects in a pair of temporal images that only planar rigid-body motion
takes place in the image domain, while cracks are treated as a type of local anomaly. The unknown motion parameters are
estimated by means of a manifold-based optimization procedure, and the obtained manifold distance (MD) measure is used
as a motion-invariant feature to describe the temporal occurrence of concrete cracks. Numerical analyses are conducted
with the use of video clips from two laboratory experiments. It is concluded in this paper that the MD-based spatial-temporal
image analysis can be an effective means for monitoring local damage of structural components that occurs and
is accompanied by structural motion induced by loading.
Tremendous progress has been achieved in image analysis and processing, and in particular, the use of partial differential
equation (PDE) methods in image analysis has proliferated in recent years. However, PDE methods have seen little
application to optical image-based structural damage detection for civil systems. This paper applies the Chan-Vese active
contour model and its level set representation to detect concrete surface damage, in this case concrete cracks, in optical images.
The detected cracks can be further characterized by extracted geometric quantities including their width, length and
area of coverage, and associated with engineering design. With regard to crack width extraction, an approximate method
is proposed, which relies on solving for a signed distance function. We test these methods by using synthetic images as
well as real multi-temporal images from a laboratory experiment. This paper illustrates that using the proposed methods,
cracks with complex topographical patterns can be successfully detected with sufficient accuracy.
Multi-temporal earth-observation imagery is now available at sub-meter accuracy and has been found very useful for
performing quick damage detection for urban areas affected by large-scale disasters. The detection of structural damage
using images taken before and after disaster events is usually modeled as a change detection problem. In this paper,
we propose a new perspective for performing change detection, where dissimilarity measures are used to extract urban
structural damage. First, image gradient magnitudes and spatial variances are used as a means to capture urban structural
features. Subsequently, a family of distribution dissimilarity measures, including: Euclidean distance, Cosine, Jeffery
divergence, and Bhattacharyya distance, are used to extract structural damage. We particularly focus on evaluating the
performance of these dissimilarity-based change detection methods under the framework of pattern classification and crossvalidation,
and with the use of a pair of bi-temporal satellite images captured before and after a major earthquake in Bam,
Iran. The paper concludes that the proposed change detection methods for urban structural damage detection, which
are conceptually simple and computationally efficient, outperform the traditional correlation analysis in terms of both
classification accuracy and tolerance to local alignment errors.
The doughnut beams with charges of 1 to 3 are generated by one and stacking two and three Liquid crystal(LC) spiral
phase plates with cell gaps of 7 μm respectively. Theoretically, any charge number can be obtained by the stacking
method. High efficiency and flexibility are the advantages of generating doughnut beams by stacking liquid crystal spiral
phase plates. The interference of doughnut beam generated by LC spiral phase plate and plane wave has been studied.
The numerical simulation results agree with the experiment.
In this paper, a numerical method is presented to design a biconical waveguide. We use this method to calculate the transmitted and radiated power of the biconical waveguide in an integrated acousto-optic modulator, then we plot the normalized power loss curves versus the taper length and get the optimum design.
An efficient shooting algorithm based on the simple-shooting method and the modified Newton-method for fiber Raman amplifier design is proposed. By introducing the Broyden's rank-one method, the time-consuming calculation of the Jacobian matrix is dramatically relieved. Numerical simulation results show that the simulation efficiency of the proposed method has been improved more than 70 percent compared with the conventional shooting method.
A new numerical optimization method assisted by functional model and improved Newton's iterations is proposed. The method would be applied to the pump power configure optimal design for the gain flatness optimization in the laser-diode discrete Fiber Raman amplifier (FRA). Compared with other optimization algorithms, the proposed improved Newton's iteration has fast convergence speed and good stability. So the method can exploit better solutions and greatly shorten the amount of run time. Two samples show the feasibility of the method with different initial variables. The comparison with Genetic algorithm (GA) is obtained.
In this paper the parameters of a CW double-clad fiber laser are theoretically analyzed, which is of important references to designing the kindred double-clad fiber lasers. This paper also offers a personalizing design scheme of double-clad fiber lasers, with the influence of some important parameters on the output power clarified.
The overlap integral of guided acousto-optic interaction is investigated theoretically. The overlap integral of YZ-LiNbO3 (Y-cut crystal, Z-propagating surface acoustic wave) is discussed with different penetration depths for TE- and TM-polarized light. Some valuable results are obtained for the design of acousto-optic devices.
A Q-Switched All-Fiber Cladding-Pumped Ytterbium-Doped Fiber Lasers using an acoustic-optic waveguide Q-switched (AOW-Q) with a pigtail fiber are studied. For AOW Q-switched, Ti-diffused YX-lithium niobate substrate was applied as optical waveguide, a SiO2/In2O3 film of thickness ~150nm as acoustic waveguide and an acoustic aperture of width 110 μm, in conjunction with N=9 finger pairs.
Remotely sensed satellite imagery of an earthquake-affected area can significantly assist in estimating the severity of infrastructure damage. Modern high-resolution satellite systems have been launched to provide users optical or Synthetic Aperture radar (SAR) data with sub-meter accuracy, which enable the possibility of sensing damage for individual infrastructure by means of pre- and post-event imagery. Herein, we focus our study on the region of Bam, Iran, which was devastated by a moment magnitude Mw = 6.6 earthquake on December 26, 2003, causing approximately 43,200 lives lost. To recognize houses within the Bam region before the earthquake, the boundary of houses are located using a combination of morphological gray-level open and intensity threshold operators. The unique aspect of this paper, as demonstrated with satellite imagery data from this event, is the use of an probabilistic framework for determining the optimal combination of morphological and intensity threshold parameters, which results in an estimated ground truth (EGT). By overlaying the EGT obtained from images before the earthquake with images of the same region after the earthquake, two statistical damage indices, including a new boundary-compactness based index proposed in this study, are compared. This comparison is presented using easily interpretable damage maps, where individual houses are rendered with colors representing the severity of damage.
A new method of gain adjustment of multipump Raman fiber amplifier is proposed and numerically demonstrated. The method utilizes the areas under the pump power evolution curves along the gain fiber as a criterion and the Newton-Raphson method is used to find the appropriate power combination of the pumps to realize the desired gain profile. The proposed method has two merits: First, it can maintain the gain profile while changing the gain magnitude to the desired value; second, it is independent of the actual scheme of the amplifier, i.e. it can be used in Raman fiber amplifiers with all kinds of pumping schemes including co-, counter-, or bi-directional pumping. Numerical simulation results are also provided to verify the proposed method and demonstrate its effectiveness.
The thermal effect in the laser diode (LD)-side-pumped solid-state laser is studied. The pump power, the temperature distribution figures and the laser beam parameters are obtained. The thermal effects under different cooling conditions are numerically calculated, as well as those in diode-end-pumped solid-state laser. The calculation results are compared with those in diode-side-pumped solid-state laser.
Raman gain in various optical fibers G652, G653, G655 and DCF (dispersion compensating fiber) and the selection of fibers in discrete broadband Raman fiber amplifiers (RFA) are studied. Using the experimental results from references, we have obtained a polynomial formula of the SRS (stimulated Raman scattering) Stokes spectrum and the effective area of the fibers by sampling and digital fitting. The effective Raman gain coefficients are calculated using the formula. Based on the formula, Raman gains of multi-wave pump RFA in different fibers are obtained with the consideration of arbitrary interaction between pump waves and signal waves. Comparing the pump power distributions and the lengths in the four optical fibers, we propose appropriate selections of optical fibers in Raman fiber amplifiers.
The effect of liquid-crystal spiral phase plates on the generation of doughnut laser beams is studied. Several parameters of the liquid-crystal (LC) are analyzed and carefully selected including birefringence of the LC, thickness, cell gap, type, topographic charge number, and applied voltage. The LC spiral phase plates have been fabricated.
We have demonstrated an effective method for suppression of coupling from a guided mode to cladding modes in a fiber grating. The UV light pulse energy, repeated frequency and exposure time are controlled and optimized during writing process of Bragg grating. We can write advanced Bragg grating using optimum UV light parameters.
A dynamic gain control (DGC) technique for the multi-wavelength-pumped fiber Raman amplifier (FRA) is presented. It introduced an all-optical feedback to inject a portion of the signal power into the system by using a variable attenuator. The stable performance of the proposed gain-clamped FRA was simulated and the noise performance was also discussed.
Compact and efficient blue light source are attractive for numerous and technical applications such as laser-based metrology, data storage, medicine, xerography, and biotechnology. Nonlinear frequency conversion remains an attractive route to achieving blue light sources. In this paper we show that 915nm laser diode pumped Yb-doped double clad fiber lasers (YDCFL) can provide efficient 978nm light. Frequency doubling ofthe 978nm line ofYDCFL can else generate blue (489nm) light. We setup theoretical model of Yb-doped double clad blue fiber laser. The threshold and Output powers at 978nm and 489nm versus the fiber length, the core diameter, the size and numerical aperture (NA) of the inner cladding, and pumped power are studied through theoretical simulation. The optimum parameters are obtained. In the design of three-level double-clad fiber lasers, we consider two main considerations: high pump brightness and an optimum balance between spectral filtering and modal gain discrimination. Atype I phase—matched BBO crystal is used to generate second harmonic light(489nm).
A computing model to calculate the small-signal gain and noise figure ofa multi-wavelength-pumped fiber Raman amplifier (FRA) was developed. The properties and several elemental principles for the design of multi-wavelength-pumped FRA were discussed and its noise figure was analyzed at the same time. Finally, a 12-wavelength-pumped FRA using WDM diode pumps with an outstanding performance such as 2.5dB flatness over 9Onm was designed by using the model.