A common source of error in particle image velocimetry (PIV) is the presence of bright spots within the images. These bright
spots are characterized by grayscale intensities much greater than the mean intensity of the image and are typically generated
by intense scattering from seed particles. The displacement of bright spots can dominate the cross-correlation calculation
within an interrogation window, and may thereby bias the resulting velocity vector. An efficient and easy-to-implement image-enhancement
procedure is described to improve PIV results when bright spots are present. The procedure, called Intensity Capping, imposes
a user-specified upper limit to the grayscale intensity of the images. The displacement calculation then better represents
the displacement of all particles in an interrogation window and the bias due to bright spots is reduced. Four PIV codes and a large set of experimental
and simulated images were used to evaluate the performance of Intensity Capping. The results indicate that Intensity Capping
can significantly increase the number of valid vectors from experimental image pairs and reduce displacement error in the
analysis of simulated images. A comparison with other PIV image-enhancement techniques shows that Intensity Capping offers
competitive performance, low computational cost, ease of implementation, and minimal modification to the images. 相似文献
We designed and operated a new system of pulsed flow modulation (PFM) two dimensional comprehensive gas chromatography (GC × GC) mass spectrometry (MS). This system is based on the combination of PFM–GC × GC with a quadrupole mass spectrometer of GC–MS via a supersonic molecular beams interface and its fly-through Cold EI ion source and applied this system for the analysis of JP8 jet fuel. PFM is a simple GC × GC modulator that does not consume cryogenic gases while providing tunable second GC × GC column injection time for enabling the use of quadrupole based mass spectrometry regardless its limited scanning speed. We analyzed JP8 jet fuel with our new PFM–GC × GC–MS with Cold EI system and found that as the second dimension GC elution time is increased the observed molecular ion mass is reduced. This unique observation that helped in improved sample compounds identification under co-elution conditions was enabled via having abundant molecular ions in Cold EI for all the fuel compounds. We named this type of analysis as PFM–GC × GC × MS. We found and discuss in this paper that PFM–GC × GC–MS with Cold EI combines improved separation of GC × GC with Cold EI benefits of tailing-free ultra-fast ion source response time and enhanced molecular ions and mass spectral isomer and isotope information for the provision of increased sample identification information.
The influence of the electrical body forces and electrical tractions on the nonlinear response of ferroelectric stack actuators is analytically investigated. While the role of the electrical body forces and tractions in the response of piezoelectric actuators is well documented (and in many cases is not significant), the questions of their effect on ferroelectric active materials is still of interest. To examine this influence, the analytical model for the electro-mechanical behavior of a ferroelectric stack actuator is augmented to account for the electrical body forces along the actuator and the electrical tractions at the material–electrode interfaces. Focusing on the effect of the electrical forces and tractions on the ferroelectric domain switching phenomenon, the model is used for the numerical analysis of a ferroelectric layer and for the comparison with the case that neglects the electrical body forces and traction. The comparison theoretically designates cases in which the effect of the electrical body forces and tractions may be prominent and other cases where the classical approach that neglects these effects can be adopted. 相似文献
The dielectric properties of zirconium dioxide (ZrO2) ceramic thin films were characterized up to 50 GHz using coplanar waveguides (CPWs) and metal–insulator–metal (MIM) capacitors
with top circular electrodes. The ZrO2 films were deposited using a chemical solution onto high-resistivity Si wafers and metal layers. The real part of the dielectric
constant of approximately 22 and 26 was extracted at 50 GHz for CPW and MIM structures, respectively, and the loss tangent
was approximately 0.09 at 50 GHz. C–V and I–V measurements were carried out to determine low-frequency and DC dielectric properties. The measurement results indicate that
ZrO2 is a promising material to be used as a dielectric layer for radio-frequency (RF) microelectromechanical systems (MEMS) capacitive
switches. 相似文献
The hypotheses that genotypic differences in salinity tolerance may result from (i) differences in global surface charge density or (ii) from differences in global Ca2+ binding were tested. An attempt was made to correlate the differing salinity tolerance of four melon cultivars with surface properties of vesicles extracted from the plasma membrane (PM) of their root cells. Surface characterization involved measurements of electrophoretic mobility and sorption of 45Ca2+ to the vesicles in the presence of varying concentrations of Ca2+, Na+ and Mg2+. Irrespective of salinity tolerance, vesicles from the four cultivars yielded similar ζ potentials under similar conditions, indicating similar global surface charge densities. Sorption studies with vesicles from two cultivars differing in salinity tolerance predicted independently this result of equal surface charge density. The estimated global binding affinities of Ca2+, Na+ and Mg2+ to the PM of both cultivars were the same with binding coefficients of 50, 0.8 and 9 M−1, respectively. Consequently, the hypotheses enumerated above to interpret genotypic differences in salinity toxicity are rejected. However, vesicles from the salt-resistant strain sorbed 19% more Ca2+ per given amount of protein in the membrane, indicating the existence of a larger number of negatively charged surface sites per given amount of protein and a smaller amount of protein per given area of membrane. Genotypic differences in site-specific Ca2+-binding affinity (e.g. at ion channels) remain a viable hypothesis for genotypic differences in salinity tolerance. 相似文献
We study queues in tandem with customer deadlines and retrials. We first consider a 2-queue Markovian system with blocking at the second queue, analyze it, and derive its stability condition. We then study a non-Markovian setting and derive the stability condition for an approximating diffusion, showing its similarity to the former condition. In the Markovian setting, we use probability generating functions and matrix analytic techniques. In the diffusion setting, we consider expectations of the first hitting times of compact sets. 相似文献