44 research outputs found
Adaptive phase-shifting algorithm for temporal phase evaluation
Most standard temporal phase-shifting algorithms evaluate the phase by computing a
windowed Fourier transform (WFT) of the intensity signal at the carrier frequency of
the system. However, displacement of the specimen during image acquisition may
cause the peak of the transform to shift away from the carrier frequency, leading to
phase errors and even unwrapping failure. We present a novel TPS method that
searches for the peak of the WFT and evaluates the phase at that frequency instead of
at the carrier frequency. The performance of this method is compared with that of
standard algorithms by using numerical simulations. Experimental results from highspeed
speckle interferometry studies of carbon fiber panels are also presented
Measurement of sub-surface delaminations in carbon fibre composites using high-speed phase-shifted speckle interferometry and temporal phase unwrapping
A high-speed phase-shifted speckle interferometer has been developed recently for studying
dynamic events. Speckle interferograms are continuously recorded by a CCD camera
operating at 1 kHz with temporal phase shifting carried out by a Pockels cell running at the
same frequency. Temporalphase unwrapping through sequences of more than 1000 frames
allows the determination of time-varying absolute displacement maps. This paper presents the
application of this speckle interferometry system to the detection and measurement of subsurface
delamination defects in carbon fibre specimens. The influence of re-referencing the
temporal phase unwrapping algorithm after different time intervals is analysed to reduce the
random phase errors produced by speckle decorrelation and vibration. The performance of
severalphase-shifting algorithms to minimize the influence of the vibration noise caused by the
vacuum pump used to load the specimen is also investigated
Speckle activity images based on the spatial variance of the phase
We propose the display of the local spatial variance of the temporal variations of the phase as an activity descriptor in dynamic speckle images. The spatial autocorrelation of the speckle intensity is calculated in sliding windows, and an estimation of the variance of the phase variations in each region of the sample is determined. The activity images obtained in this way depict some interesting features and in some cases they could be related to physical magnitudes in the samples. A simulation is presented, and examples corresponding to usual study cases are also shown, namely, fruit bruising and paint drying
Effects of random vibration in high-speed phase-shifting speckle pattern interferometry
The influence of random vibrations on a dynamic phase shifting speckle
pattern interferometer, in which phase difference evaluation is performed using
temporal phase shifting and temporal phase unwrapping, is investigated by means of
experiments and numerical simulations. A well-defined velocity spectral density
function, typical of the spectra found under non-vibration-isolated conditions, is used
throughout. Five phase-shifting formulae are studied, with camera framing rates (1,2
and 4 kHz) typical of current dynamic speckle pattern interferometers. Two main
aspects were evaluated: firstly the unwrapping reliability, and secondly the noise
induced in the phase maps by the vibration. The former was found to be a significant
constraint, even for peak velocities well below the Nyquist velocity limit of the
interferometer, and is therefore likely to be more important than the latter in many
applications. Three analytical criteria for determining the expected unwrapping
success rate are proposed and their predictions compared with the measured values.
It is demonstrated that shorter sampling windows and higher framing rates are
preferred in order to increase the unwrapping success rate, but that longer windows
reduce the root mean square error in the phase change maps due to the vibration
Speckle activity images based on the spatial variance of the phase
We propose the display of the local spatial variance of the temporal variations of the phase as an activity descriptor in dynamic speckle images. The spatial autocorrelation of the speckle intensity is calculated in sliding windows, and an estimation of the variance of the phase variations in each region of the sample is determined. The activity images obtained in this way depict some interesting features and in some cases they could be related to physical magnitudes in the samples. A simulation is presented, and examples corresponding to usual study cases are also shown, namely, fruit bruising and paint drying.Facultad de IngenierÃa (FI)Centro de Investigaciones Ópticas (CIOp
Speckle activity images based on the spatial variance of the phase
We propose the display of the local spatial variance of the temporal variations of the phase as an activity descriptor in dynamic speckle images. The spatial autocorrelation of the speckle intensity is calculated in sliding windows, and an estimation of the variance of the phase variations in each region of the sample is determined. The activity images obtained in this way depict some interesting features and in some cases they could be related to physical magnitudes in the samples. A simulation is presented, and examples corresponding to usual study cases are also shown, namely, fruit bruising and paint drying.Facultad de IngenierÃa (FI)Centro de Investigaciones Ópticas (CIOp
Speckle activity images based on the spatial variance of the phase
We propose the display of the local spatial variance of the temporal variations of the phase as an activity descriptor in dynamic speckle images. The spatial autocorrelation of the speckle intensity is calculated in sliding windows, and an estimation of the variance of the phase variations in each region of the sample is determined. The activity images obtained in this way depict some interesting features and in some cases they could be related to physical magnitudes in the samples. A simulation is presented, and examples corresponding to usual study cases are also shown, namely, fruit bruising and paint drying.Facultad de IngenierÃa (FI)Centro de Investigaciones Ópticas (CIOp
Are Foreign Firms Privileged By Their Host Governments? Evidence From The 2000 World Business Environment Survey
Using the data from World Business Environment Survey (WBES) on over 10,000 firms across eighty one countries, this paper finds preliminary evidence that foreign firms enjoy significant regulatory advantages - as perceived by the firms themselves - over domestic firms. The findings on regulatory advantages of foreign firms hold with a variety of alternative measures of regulations and with or without firm- and country-level attributes and industry and country controls. There is also evidence that foreign firms' regulatory advantages are especially substantial vis-a-vis the politically weak domestic firms. Furthermore, the regulatory advantages of foreign firms appear stronger in corrupt countries than in non-corrupt countries
Evidence that the 5p12 Variant rs10941679 Confers Susceptibility to Estrogen Receptor-Positive Breast Cancer through FGF10 and MRPS30 Regulation
Genome-wide association studies (GWASs) have revealed increased breast cancer risk associated with multiple genetic variants at 5p12. Here, we report the fine mapping of this locus using data from 104,660 subjects from 50 case-control studies in the Breast Cancer Association Consortium (BCAC). With data for 3,365 genotyped and imputed SNPs across a 1 Mb region (positions 44,394,495–45,364,167; NCBI build 37), we found evidence for at least three independent signals: the strongest signal, consisting of a single SNP rs10941679, was associated with risk of estrogen receptor-positive (ER+) breast cancer (per-g allele OR ER+ = 1.15; 95% CI 1.13–1.18; p = 8.35 × 10−30). After adjustment for rs10941679, we detected signal 2, consisting of 38 SNPs more strongly associated with ER-negative (ER−) breast cancer (lead SNP rs6864776: per-a allele OR ER− = 1.10; 95% CI 1.05–1.14; p conditional = 1.44 × 10−12), and a single signal 3 SNP (rs200229088: per-t allele OR ER+ = 1.12; 95% CI 1.09–1.15; p conditional = 1.12 × 10−05). Expression quantitative trait locus analysis in normal breast tissues and breast tumors showed that the g (risk) allele of rs10941679 was associated with increased expression of FGF10 and MRPS30. Functional assays demonstrated that SNP rs10941679 maps to an enhancer element that physically interacts with the FGF10 and MRPS30 promoter regions in breast cancer cell lines. FGF10 is an oncogene that binds to FGFR2 and is overexpressed in ∼10% of human breast cancers, whereas MRPS30 plays a key role in apoptosis. These data suggest that the strongest signal of association at 5p12 is mediated through coordinated activation of FGF10 and MRPS30, two candidate genes for breast cancer pathogenesis