1,335 research outputs found
Magnification relations of quad lenses and applications on Einstein crosses
In this work, we mainly study the magnification relations of quad lens models
for cusp, fold and cross configurations. By dividing and ray-tracing in
different image regions, we numerically derive the positions and magnifications
of the four images for a point source lying inside of the astroid caustic.
Then, based on the magnifications, we calculate the signed cusp and fold
relations for the singular isothermal elliptical lenses. The signed fold
relation map has positive and negative regions, and the positive region is
usually larger than the negative region as has been confirmed before. It can
also explain that for many observed fold image pairs, the fluxes of the Fermat
minimum images are apt to be larger than those of the saddle images. We define
a new quantity cross relation which describes the magnification discrepancy
between two minimum images and two saddle images. Distance ratio is also
defined as the ratio of the distance of two saddle images to that of two
minimum images. We calculate the cross relations and distance ratios for nine
observed Einstein crosses. In theory, for most of the quad lens models, the
cross relations decrease as the distance ratios increase. In observation, the
cross relations of the nine samples do not agree with the quad lens models very
well, nevertheless, the cross relations of the nine samples do not give obvious
evidence for anomalous flux ratio as the cusp and fold types do. Then, we
discuss several reasons for the disagreement, and expect good consistencies for
more precise observations and better lens models in the future.Comment: 12 pages, 11 figures, accepted for publication in MNRA
An Inductive Sensor for Real Time Measurement of Plantar Normal and Shear Forces Distribution
Goal: The objective of this article is to demonstrate a multiplexed inductive force sensor for simultaneously measuring normal force and shear forces on a foot. Methods: The sensor measures the normal force and shear forces by monitoring the inductance changes of three planar sensing coils. Resonance frequency division multiplexing was applied to signals from the multiple sensing coils, making it feasible to simultaneously measure the three forces (normal force, shear forces in x and y axis) on a foot using only one set of measurement electronics with high sensitivity and resolution. Results: The testing results of the prototype sensor have shown that the sensor is capable of measuring normal force ranging from 0 to 800 N and shear forces ranging from 0 to 130 N in real time. Conclusion: With its high resolution, high sensitivity and the capability of monitoring forces at different positions of a foot simultaneously, this sensor can be potentially used for real time measurement of plantar normal force and shear forces distribution on diabetes patient’s foot. Significance: Real time monitoring of the normal force and shear forces on diabetes patient’s foot can provide useful information for physicians and diabetes patients to take actions in preventing foot ulceration
Distributed Robust Learning-Based Backstepping Control Aided with Neurodynamics for Consensus Formation Tracking of Underwater Vessels
This paper addresses distributed robust learning-based control for consensus
formation tracking of multiple underwater vessels, in which the system
parameters of the marine vessels are assumed to be entirely unknown and subject
to the modeling mismatch, oceanic disturbances, and noises. Towards this end,
graph theory is used to allow us to synthesize the distributed controller with
a stability guarantee. Due to the fact that the parameter uncertainties only
arise in the vessels' dynamic model, the backstepping control technique is then
employed. Subsequently, to overcome the difficulties in handling time-varying
and unknown systems, an online learning procedure is developed in the proposed
distributed formation control protocol. Moreover, modeling errors,
environmental disturbances, and measurement noises are considered and tackled
by introducing a neurodynamics model in the controller design to obtain a
robust solution. Then, the stability analysis of the overall closed-loop system
under the proposed scheme is provided to ensure the robust adaptive performance
at the theoretical level. Finally, extensive simulation experiments are
conducted to further verify the efficacy of the presented distributed control
protocol
Expressions of Hippocampal Mineralocorticoid Receptor (MR) and Glucocorticoid Receptor (GR) in the Single-Prolonged Stress-Rats
Post-traumatic stress disorder (PTSD) is a stress-related mental disorder caused by traumatic experience. Single-prolonged stress (SPS) is one of the animal models proposed for PTSD. Rats exposed to SPS showed enhanced inhibition of the hypothalamo-pituitary-adrenal (HPA) axis, which has been reliably reproduced in patients with PTSD. Mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) in the hippocampus regulate HPA axis by glucocorticoid negative feedback. Abnormalities in negative feedback are found in PTSD, suggesting that GR and MR might be involved in the pathophysiology of these disorders
Distributed Neurodynamics-Based Backstepping Optimal Control for Robust Constrained Consensus of Underactuated Underwater Vehicles Fleet
Robust constrained formation tracking control of underactuated underwater
vehicles (UUVs) fleet in three-dimensional space is a challenging but practical
problem. To address this problem, this paper develops a novel consensus based
optimal coordination protocol and a robust controller, which adopts a
hierarchical architecture. On the top layer, the spherical coordinate transform
is introduced to tackle the nonholonomic constraint, and then a distributed
optimal motion coordination strategy is developed. As a result, the optimal
formation tracking of UUVs fleet can be achieved, and the constraints are
fulfilled. To realize the generated optimal commands better and, meanwhile,
deal with the underactuation, at the lower-level control loop a neurodynamics
based robust backstepping controller is designed, and in particular, the issue
of "explosion of terms" appearing in conventional backstepping based
controllers is avoided and control activities are improved. The stability of
the overall UUVs formation system is established to ensure that all the states
of the UUVs are uniformly ultimately bounded in the presence of unknown
disturbances. Finally, extensive simulation comparisons are made to illustrate
the superiority and effectiveness of the derived optimal formation tracking
protocol.Comment: This paper is accepted by IEEE Transactions on Cybernetic
Recent progress in antiferromagnetic dynamics
Spintronics, since its inception, has mainly focused on ferromagnetic
materials for manipulating the spin degree of freedom in addition to the charge
degree of freedom, whereas much less attention has been paid to
antiferromagnetic materials. Thanks to the advances of micro-nano-fabrication
techniques and the electrical control of the N\'eel order parameter,
antiferromagnetic spintronics is booming as a result of abundant room
temperature materials, robustness against external fields and dipolar coupling,
and rapid dynamics in the terahertz regime. For the purpose of applications of
antiferromagnets, it is essential to have a comprehensive understanding of the
antiferromagnetic dynamics at the microscopic level. Here, we first review the
general form of equations that govern both antiferromagnetic and ferrimagnetic
dynamics. This general form unifies the previous theories in the literature. We
also provide a survey for the recent progress related to antiferromagnetic
dynamics, including the motion of antiferromagnetic domain walls and skyrmions,
the spin pumping and quantum antiferromagnetic spintronics. In particular, open
problems in several topics are outlined. Furthermore, we discuss the
development of antiferromagnetic quantum magnonics and its potential
integration with modern information science and technology.Comment: 7 pages, 2 figure
Entanglement in spin-1/2 dimerized Heisenberg systems
We study entanglement in dimerized Heisenberg systems. In particular, we give
exact results of ground-state pairwise entanglement for the four-qubit model by
identifying a Z_2 symmetry. Although the entanglements cannot identify the
critical point of the system, the mean entanglement of nearest-neighbor qubits
really does, namely, it reaches a maximum at the critical point.Comment: Four pages, three figures, accepted in Communications in Theoretical
Physic
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