2,899 research outputs found
The eleven antenna: a compact low-profile decade bandwidth dual polarized feed for reflector antennas
A novel dual polarized ultrawide-band (UWB) feed with a decade bandwidth is presented for use in both single and dual reflector antennas. The feed has nearly constant beam width and 11 dBi directivity over at least a decade bandwidth. The feed gives an aperture efficiency of the reflector of 66% or better over a decade bandwidth when the subtended angle toward the sub or main reflector is about 53°, and an overall efficiency better than 47% including mismatch. The return loss is better than 5 dB over a decade bandwidth. The calculated results have been verified with measurements on a linearly polarized lab model. The feed has no balun as it is intended to be integrated with an active 180° balun and receiver. The feed is referred to as the Eleven antenna because its basic configuration is two parallel dipoles 0.5 wavelengths apart and because it can be used over more than a decade bandwidth with 11 dBi directivity. We also believe that 11 dB return loss is achievable in the near future
Machine Learning in Molecular Dynamics Simulations of Biomolecular Systems
Machine learning (ML) has emerged as a pervasive tool in science,
engineering, and beyond. Its success has also led to several synergies with
molecular dynamics (MD) simulations, which we use to identify and characterize
the major metastable states of molecular systems. Typically, we aim to
determine the relative stabilities of these states and how rapidly they
interchange. This information allows mechanistic descriptions of molecular
mechanisms, enables a quantitative comparison with experiments, and facilitates
their rational design. ML impacts all aspects of MD simulations -- from
analyzing the data and accelerating sampling to defining more efficient or more
accurate simulation models.Comment: 36 pages, 4 figure
Implicit Transfer Operator Learning: Multiple Time-Resolution Surrogates for Molecular Dynamics
Computing properties of molecular systems rely on estimating expectations of
the (unnormalized) Boltzmann distribution. Molecular dynamics (MD) is a broadly
adopted technique to approximate such quantities. However, stable simulations
rely on very small integration time-steps (), whereas
convergence of some moments, e.g. binding free energy or rates, might rely on
sampling processes on time-scales as long as , and these
simulations must be repeated for every molecular system independently. Here, we
present Implict Transfer Operator (ITO) Learning, a framework to learn
surrogates of the simulation process with multiple time-resolutions. We
implement ITO with denoising diffusion probabilistic models with a new SE(3)
equivariant architecture and show the resulting models can generate
self-consistent stochastic dynamics across multiple time-scales, even when the
system is only partially observed. Finally, we present a coarse-grained
CG-SE3-ITO model which can quantitatively model all-atom molecular dynamics
using only coarse molecular representations. As such, ITO provides an important
step towards multiple time- and space-resolution acceleration of MD.Comment: 21 pages, 10 figure
A scalable approach to the computation of invariant measures for high-dimensional Markovian systems
Abstract The Markovian invariant measure is a central concept in many disciplines. Conventional numerical techniques for data-driven computation of invariant measures rely on estimation and further numerical processing of a transition matrix. Here we show how the quality of data-driven estimation of a transition matrix crucially depends on the validity of the statistical independence assumption for transition probabilities. Moreover, the cost of the invariant measure computation in general scales cubically with the dimension - and is usually unfeasible for realistic high-dimensional systems. We introduce a method relaxing the independence assumption of transition probabilities that scales quadratically in situations with latent variables. Applications of the method are illustrated on the Lorenz-63 system and for the molecular dynamics (MD) simulation data of the α-synuclein protein. We demonstrate how the conventional methodologies do not provide good estimates of the invariant measure based upon the available α-synuclein MD data. Applying the introduced approach to these MD data we detect two robust meta-stable states of α-synuclein and a linear transition between them, involving transient formation of secondary structure, qualitatively consistent with previous purely experimental reports
Sensory innervation of the guinea pig colon and rectum compared using retrograde tracing and immunohistochemistry.
Embargoed until 2 April 2017 as per publisher's policy
Coupled Minimal Models with and without Disorder
We analyse in this article the critical behavior of -state Potts
models coupled to -state Potts models () with and
without disorder. The technics we use are based on perturbed conformal
theories. Calculations have been performed at two loops. We already find some
interesting situations in the pure case for some peculiar values of and
with new tricritical points. When adding weak disorder, the results we obtain
tend to show that disorder makes the models decouple. Therefore, no relations
emerges, at a perturbation level, between for example the disordered -state Potts model and the two disordered -state Potts models
(), despite their central charges are similar according to recent
numerical investigations.Comment: 45 pages, Latex, 3 PS figure
3D Visual Tracking of an Articulated Robot in Precision Automated Tasks
Abstract: The most compelling requirements for visual tracking systems are a high detection accuracy and an adequate processing speed. However, the combination between the two requirements in real world applications is very challenging due to the fact that more accurate tracking tasks often require longer processing times, while quicker responses for the tracking system are more prone to errors, therefore a trade-off between accuracy and speed, and vice versa is required. This paper aims to achieve the two requirements together by implementing an accurate and time efficient tracking system. In this paper, an eye-to-hand visual system that has the ability to automatically track a moving target is introduced. An enhanced Circular Hough Transform (CHT) is employed for estimating the trajectory of a spherical target in three dimensions, the colour feature of the target was
carefully selected by using a new colour selection process, the process relies on the use of a colour segmentation method (Delta E) with the CHT algorithm for finding the proper colour of the tracked target, the target was attached to the six degree of freedom (DOF) robot end-effector that performs a pick-and-place task. A cooperation of two Eye-to Hand cameras with their image Averaging filters are used for obtaining clear and steady images. This paper also examines a new technique for generating and controlling the observation search window in order to increase the computational speed of the tracking system, the techniques is named Controllable Region of interest based on Circular Hough
Transform (CRCHT). Moreover, a new mathematical formula is introduced for updating the depth
information of the vision system during the object tracking process. For more reliable and accurate tracking, a simplex optimization technique was employed for the calculation of the parameters for camera to robotic transformation matrix. The results obtained show the applicability of the proposed approach to track the moving robot with an overall tracking error of 0.25 mm. Also, the effectiveness of CRCHT technique in saving up to 60% of the overall time required for image processing
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