3,951 research outputs found
Contrastive Learning of Person-independent Representations for Facial Action Unit Detection
Facial action unit (AU) detection, aiming to classify AU present in the
facial image, has long suffered from insufficient AU annotations. In this
paper, we aim to mitigate this data scarcity issue by learning AU
representations from a large number of unlabelled facial videos in a
contrastive learning paradigm. We formulate the self-supervised AU
representation learning signals in two-fold: (1) AU representation should be
frame-wisely discriminative within a short video clip; (2) Facial frames
sampled from different identities but show analogous facial AUs should have
consistent AU representations. As to achieve these goals, we propose to
contrastively learn the AU representation within a video clip and devise a
cross-identity reconstruction mechanism to learn the person-independent
representations. Specially, we adopt a margin-based temporal contrastive
learning paradigm to perceive the temporal AU coherence and evolution
characteristics within a clip that consists of consecutive input facial frames.
Moreover, the cross-identity reconstruction mechanism facilitates pushing the
faces from different identities but show analogous AUs close in the latent
embedding space. Experimental results on three public AU datasets demonstrate
that the learned AU representation is discriminative for AU detection. Our
method outperforms other contrastive learning methods and significantly closes
the performance gap between the self-supervised and supervised AU detection
approaches
Weak measurement combined with quantum delayed-choice experiment and implementation in optomechanical system
Weak measurement [1,19] combined with quantum delayed-choice experiment that
use quantum beam splitter instead of the beam splitter give rise to a
surprising amplification effect, i.e., counterintuitive negative amplification
effect. We show that this effect is caused by the wave and particle behaviours
of the system to be and can't be explained by a semiclassical wave theory, due
to the entanglement of the system and the ancilla in quantum beam splitter. The
amplification mechanism about wave-particle duality in quantum mechanics lead
us to a scheme for implementation of weak measurement in optomechanical system
Cooling mechanical resonators to quantum ground state from room temperature
Ground-state cooling of mesoscopic mechanical resonators is a fundamental
requirement for test of quantum theory and for implementation of quantum
information. We analyze the cavity optomechanical cooling limits in the
intermediate coupling regime, where the light-enhanced optomechanical coupling
strength is comparable with the cavity decay rate. It is found that in this
regime the cooling breaks through the limits in both the strong and weak
coupling regimes. The lowest cooling limit is derived analytically at the
optimal conditions of cavity decay rate and coupling strength. In essence,
cooling to the quantum ground state requires , with being the mechanical quality factor and
being the thermal phonon number. Remarkably, ground-state
cooling is achievable starting from room temperature, when mechanical
-frequency product , and both of the
cavity decay rate and the coupling strength exceed the thermal decoherence
rate. Our study provides a general framework for optimizing the backaction
cooling of mesoscopic mechanical resonators
Microwave Power Measurements: Standards and Transfer Techniques
In this chapter, precision power measurement, which is probably the most important area in RF and microwave metrology, will be discussed. Firstly, the background of RF and microwave power measurements and standards will be introduced. Secondly, the working principle of primary power standard (i.e., microcalorimeter) will be described, followed by the discussions of direct comparison transfer technique. Finally, there will be some discussions about the performance evaluation and uncertainty estimation for microwave power measurements
Flame Boundary Measurement Using an Electrostatic Sensor Array
Flame boundary is an important geometrical characteristic for the evaluation of flame properties such as heat release rate and radiation. Reliable and accurate measurement of flame boundary is desirable for the prediction of flame structure and the optimization of combustion systems. Such measurement will inform the designers and operators of the combustion systems. This paper presents for the first time a study of using an electrostatic sensor array for flame boundary measurement. The electrostatic sensor is placed in the vicinity of the flame to sense its movement through charge transfer. The principle, design, implementation and assessment of a measurement system based on this methodology are introduced. Comparative experimental investigations with a digital camera conducted on a laboratory-scale combustion test rig show that the electrostatic sensor can respond to the variation of the distance between the electrode and the flame boundary. Reconstruction of the flame boundary is achieved using a set of distance measurements obtained from a sensor array. For diffusion flames over the range of fuel flow rate 0.60-0.80 L/min and premixed flames over the range of equivalence ratio 1.27-3.81, experimental results show that the measurement system is capable of providing reliable measurement of the flame boundary. The correlation coefficients under all test conditions are mostly larger than 0.96, the mean relative errors within 7.4% and the relative root mean square errors within 0.09. More accurate flame boundary measurements are achieved for diffusion flames. In addition, the overall polarity of charges in a flame can be determined from the polarity of the sensor signal
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