21,469 research outputs found
Complementary weak-value amplification with concatenated postselections
We measure a transverse momentum kick in a Sagnac interferometer using
weak-value amplification with two postselections. The first postselection is
controlled by a polarization dependent phase mismatch between both paths of a
Sagnac interferometer and the second postselection is controlled by a polarizer
at the exit port. By monitoring the darkport of the interferometer, we study
the complementary amplification of the concatenated postselections, where the
polarization extinction ratio is greater than the contrast of the spatial
interference. In this case, we find an improvement in the amplification of the
signal of interest by introducing a second postselection to the system
Can Anomalous Amplification be Attained Without Postselection?
We present a parameter estimation technique based on performing joint
measurements of a weak interaction away from the weak-value-amplification
approximation. Two detectors are used to collect full statistics of the
correlations between two weakly entangled degrees of freedom. Without the need
of postselection, the protocol resembles the anomalous amplification of an
imaginary-weak-value-like response. The amplification is induced in the
difference signal of both detectors allowing robustness to different sources of
technical noise, and offering in addition the advantages of balanced signals
for precision metrology. All of the Fisher information about the parameter of
interest is collected, and a phase controls the amplification response. We
experimentally demonstrate the proposed technique by measuring polarization
rotations in a linearly polarized laser pulse. The effective sensitivity and
precision of a split detector is increased when compared to a conventional
continuous-wave balanced detection technique
Vortex dynamics
Vortex flows of interest to aerodynamicists cover a wide range of scales from a fraction of an inch in boundary layer flows to many feet in wake flows. In many applications these flows are poorly understood and, due to their complexity, present a challenge both analytically and experimentally. Four topics representing the spectrum of experimental and analytical vortex research are presented
Sub-Pixel Technique for Time Series Analysis of Shoreline Changes Based on Multispectral Satellite Imagery
The measurement and monitoring of shoreline changes are of great interest to coastal managers and engineers. Shoreline change information can be crucial for the assessment of coastal disasters, design of coastal infrastructure and protection of coastal environment. This chapter presents shoreline change monitoring based on multispectral satellite imagery and sub-pixel technique. Firstly, a brief introduction of shoreline definitions and indicators is given. Sub-pixel techniques for shoreline mapping on multispectral satellite images are then introduced. Following that, a brief review of existing research studies of long-term shoreline change monitoring based on multispectral imagery is given. Subsequently, a case study of sub-pixel shoreline change monitoring at the northern Gold Coast on the east coast of Australia is presented. By comparing the longshore averaged beach widths at seven representative transects from Landsat with those from Argus imaging data, the RMSEs range from 9.1 to 12.3 m and the correlations are all no less than 0.7. Annual means and variabilities of beach widths were estimated without significant differences from the reference data for most of the results. Finally, conclusions and recommendations for future work are given
Multiple mating and its relationship to brood size in pregnant fishes versus pregnant mammals and other viviparous vertebrates.
We summarize the literature on rates of multiple paternity and sire numbers per clutch in viviparous fishes vs. mammals, two vertebrate groups in which pregnancy is common but entails very different numbers of embryos (for species surveyed, piscine broods averaged >10-fold larger than mammalian litters). As deduced from genetic parentage analyses, multiple mating by the pregnant sex proved to be common in assayed species but averaged significantly higher in fish than mammals. However, within either of these groups we found no significant correlations between brood size and genetically deduced incidence of multiple mating by females. Overall, these findings offer little support for the hypothesis that clutch size in pregnant species predicts the outcome of selection for multiple mating by brooders. Instead, whatever factors promote multiple mating by members of the gestating sex seem to do so in surprisingly similar ways in live-bearing vertebrates otherwise as different as fish and mammals. Similar conclusions emerged when we extended the survey to viviparous amphibians and reptiles. One notion consistent with these empirical observations is that although several fitness benefits probably accrue from multiple mating, logistical constraints on mate-encounter rates routinely truncate multiple mating far below levels that otherwise could be accommodated, especially in species with larger broods. We develop this concept into a "logistical constraint hypothesis" that may help to explain these mating outcomes in viviparous vertebrates. Under the logistical constraint hypothesis, propensities for multiple mating in each species register a balance between near-universal fitness benefits from multiple mating and species-idiosyncratic logistical limits on polygamy
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