scholarly journals Mixed quantum/classical theory for inelastic scattering of asymmetric-top-rotor + atom in the body-fixed reference frame and application to the H2O + He system

2014 ◽  
Vol 141 (11) ◽  
pp. 114304 ◽  
Author(s):  
Alexander Semenov ◽  
Marie-Lise Dubernet ◽  
Dmitri Babikov
Keyword(s):  
Inelastic Scattering ◽  
Reference Frame ◽  
Classical Theory ◽  
The Body ◽  
Fixed Reference ◽  
Asymmetric Top

Rankine Source Method for Seakeeping Analysis in Shallow Water

2014 ◽  
Author(s):  
Alexander von Graefe
Keyword(s):  
Boundary Condition ◽  
Shallow Water ◽  
Reference Frame ◽  
The Body ◽  
Forward Speed ◽  
Flat Bottom ◽  
Source Method ◽  
Rankine Source ◽  
Perturbation Potential ◽  
Fixed Reference

Following Hachmann approach, Söding’s Rankine source method describes the steady perturbation potential in the body-fixed reference frame. This is beneficial for seakeeping predictions at forward speed, because error-prone m-terms do not occur in the boundary condition on the ship hull. Although similar terms arise in the boundary condition on the free surface, numerical inaccuracies in these terms have much less influence on the behaviour of the ship than in the traditional approach, where m-terms are evaluated on the hull. The periodic flow is linearised with respect to the amplitude of the incident wave, taking into account the steady ship wave. A problem arises for shallow water problems if the Hachmann approach is used. For the shallow water problem, the boundary condition ‘no flow through the bottom’ must be fulfilled. Usually, this is done using image sources. If the steady perturbation potential is described in the body-fixed reference frame, this is not possible directly. This paper extends the Hachmann approach to treat this issue. Following the usual procedure for steady flow calculation, the boundary condition at the flat bottom of the steady problem is realised using image sources. For seakeeping computations, the steady perturbation potential is split into two parts, modelled respectively by steady sources above and below the flat bottom. The first part is assumed to be constant in the body-fixed reference frame, whereas the second part is assumed to be constant in the reference frame of the mirror image of the ship. This extended Hachmann approach fulfils the boundary condition at the flat bottom analytically. Computed ship motions with and without forward speed in shallow water are validated by model test results from Flanders Hydraulics Research, Antwerp, and from TU Berlin.

Finding the jerk properties of multi-body systems using helicoidal vector fields

2008 ◽  
Vol 222 (11) ◽  
pp. 2217-2229 ◽  
Author(s):  
J Gallardo-Alvarado ◽  
H Orozco-Mendoza ◽  
R Rodríguez-Castro
Keyword(s):  
Reference Frame ◽  
Vector Fields ◽  
Time Derivative ◽  
The Body ◽  
Body System ◽  
Third Order ◽  
Numerical Examples ◽  
Multi Body

In this contribution, the kinematic angular and linear third-order properties, also known as jerk analysis, of a multi-body system are determined applying the concept of helicoidal vector fields. The reduced acceleration state, or accelerator, of the body of interest, with respect to a reference frame, is obtained as the time derivative, via a helicoidal field, of the velocity state, also known as the infinitesimal twist. Following that trend, the reduced jerk state, or jerkor, is obtained as the time derivative of the accelerator. The computation of the instantaneous centre of jerk, with its corresponding ellipsoid of jerk, is also included. The expressions thus obtained are extended systematically to multi-body systems. Two numerical examples are provided in order to illustrate the potential of the presented method.

A Neural Network Model of Flexible Spatial Updating

2004 ◽  
Vol 91 (4) ◽  
pp. 1608-1619 ◽  
Author(s):  
Robert L. White ◽  
Lawrence H. Snyder
Keyword(s):  
Neural Network ◽  
Reference Frame ◽  
Spatial Information ◽  
Target Location ◽  
Target Position ◽  
Spatial Location ◽  
Spatial Updating ◽  
Gaze Shift ◽  
Fixed Reference ◽  
Gaze Position

Neurons in many cortical areas involved in visuospatial processing represent remembered spatial information in retinotopic coordinates. During a gaze shift, the retinotopic representation of a target location that is fixed in the world (world-fixed reference frame) must be updated, whereas the representation of a target fixed relative to the center of gaze (gaze-fixed) must remain constant. To investigate how such computations might be performed, we trained a 3-layer recurrent neural network to store and update a spatial location based on a gaze perturbation signal, and to do so flexibly based on a contextual cue. The network produced an accurate readout of target position when cued to either reference frame, but was less precise when updating was performed. This output mimics the pattern of behavior seen in animals performing a similar task. We tested whether updating would preferentially use gaze position or gaze velocity signals, and found that the network strongly preferred velocity for updating world-fixed targets. Furthermore, we found that gaze position gain fields were not present when velocity signals were available for updating. These results have implications for how updating is performed in the brain.

scholarly journals On Manipulation of Objects in Three-Fingered Grasp

1995 ◽  
Vol 117 (4) ◽  
pp. 561-565 ◽  
Author(s):  
D. P. Chevallier ◽  
S. Payandeh
Keyword(s):  
Reference Frame ◽  
New Method ◽  
Inner Product ◽  
Product Spaces ◽  
End Effector ◽  
Inner Product Spaces ◽  
Contact Points ◽  
Fixed Reference ◽  
Fine Manipulation

Manipulation of the grasped object is defined as the ability of the mechanical end-effector to create an instantaneous motion of the object with respect to a fixed reference frame (e.g., palm reference frame). This class of manipulation is usually referred to as the fine manipulation whereas a collection of all these instantaneous motions of the object is referred to as the gross manipulation. This paper presents a new method where for a given desired twist of the grasped object, the instantaneous motions of the fingertips can be determined. The results of the paper are divided into two parts. First, for the case where the motion of the object is created through motions of the fingertip in off-tangent planes to the object at the contact points. Second, where a class of motion of the grasped object is achieved through motions of the fingertips which are restricted to the tangent planes. The method of this paper utilizes screw geometry, inner product spaces and information regarding grasp configuration. The method is also illustrated through examples.

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