scholarly journals Internal Variability of the Winter Stratosphere. Part I: Time-Independent Forcing

2006 ◽  
Vol 63 (11) ◽  
pp. 2758-2776 ◽  
Author(s):  
R. K. Scott ◽  
L. M. Polvani
Keyword(s):  
Radiative Forcing ◽  
Degrees Of Freedom ◽  
Planetary Wave ◽  
Three Dimensional ◽  
Polar Vortex ◽  
Internal Variability ◽  
Wave Forcing ◽  
Wide Range ◽  
External Sources ◽  
Stratospheric Variability

Abstract This paper examines the nature and robustness of internal stratospheric variability, namely the variability resulting from the internal dynamics of the stratosphere itself, as opposed to that forced by external sources such as the natural variability of the free troposphere. Internal stratospheric variability arises from the competing actions of radiative forcing, which under perpetual winter conditions strengthens the polar vortex, and planetary wave breaking, which weakens it. The results from a stratosphere-only model demonstrate that strong internal stratospheric variability, consisting of repeated sudden warming-type events, exists over a wide range of realistic radiative and wave forcing conditions, and is largely independent of other physical and numerical parameters. In particular, the coherent form of the variability persists as the number of degrees of freedom is increased, and is therefore not an artifact of severe model truncation. Various diagnostics, including three-dimensional representations of the potential vorticity, illustrate that the variability is determined by the vertical structure of the vortex and the extent to which upward wave propagation is favored or inhibited. In this paper, the variability arising from purely internal stratosphere dynamics is isolated by specifying thermal and wave forcings that are completely time independent. In a second paper, the authors investigate the relative importance of internal and external variability by considering time-dependent wave forcing as a simple representation of tropospheric variability.

Do Arm Postures Vary With the Speed of Reaching?

1999 ◽  
Vol 81 (5) ◽  
pp. 2582-2586 ◽  
Author(s):  
Kiisa C. Nishikawa ◽  
Sara T. Murray ◽  
Martha Flanders
Keyword(s):  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Optimal Solution ◽  
Reaching Movements ◽  
Total Force ◽  
Joint Torques ◽  
Dynamic Factors ◽  
Human Arm ◽  
Wide Range ◽  
Dynamic Forces

Do arm postures vary with the speed of reaching? For reaching movements in one plane, the hand has been observed to follow a similar path regardless of speed. Recent work on the control of more complex reaching movements raises the question of whether a similar “speed invariance” also holds for the additional degrees of freedom. Therefore we examined human arm movements involving initial and final hand locations distributed throughout the three-dimensional (3D) workspace of the arm. Despite this added complexity, arm kinematics (summarized by the spatial orientation of the “plane of the arm” and the 3D curvature of the hand path) changed very little for movements performed over a wide range of speeds. If the total force (dynamic + quasistatic) had been optimized by the control system (e.g., as in a minimization of the change in joint torques or the change in muscular forces), the optimal solution would change with speed; slow movements would reflect the minimal antigravity torques, whereas fast movements would be more strongly influenced by dynamic factors. The speed-invariant postures observed in this study are instead consistent with a hypothesized optimization of only the dynamic forces.

scholarly journals Internal Variability of the Winter Stratosphere. Part II: Time-Dependent Forcing

2008 ◽  
Vol 65 (7) ◽  
pp. 2375-2388 ◽  
Author(s):  
R. K. Scott ◽  
L. M. Polvani ◽  
D. W. Waugh
Keyword(s):  
Lower Boundary ◽  
Polar Vortex ◽  
Internal Variability ◽  
Time Dependent ◽  
Random Wave ◽  
Frequency Locking ◽  
Wave Forcing ◽  
Wave Flux ◽  
Time Periodic ◽  
Zero Time

Abstract This paper considers the effect of time-dependent lower boundary wave forcing on the internal variability found to appear spontaneously in a stratosphere-only model when the forcing is perfectly steady. While the time-dependent forcing is found to modulate the internal variability, leading in some cases to frequency locking of the upper-stratospheric response to the forcing, the temporal and spatial structure of the variability remains similar to the case when the forcing is time independent. Experiments with a time-periodic modulation of the forcing amplitude indicate that the wave flux through the lower boundary is only partially related to the instantaneous forcing, but is more significantly influenced by the condition of the polar vortex itself. In cases of purely random wave forcing with zero time mean, the stratospheric response is similar to that obtained with steady forcing of magnitude equal to the root-mean-square of the time-varying forcing.

On a Leray–α model of turbulence

2005 ◽  
Vol 461 (2055) ◽  
pp. 629-649 ◽  
Author(s):  
Alexey Cheskidov ◽  
Darryl D. Holm ◽  
Eric Olson ◽  
Edriss S. Titi
Keyword(s):  
Power Law ◽  
Upper Bound ◽  
Empirical Data ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Large Eddy Simulation Model ◽  
Eddy Simulation ◽  
Wide Range ◽  
Three Dimensional Models

In this paper we introduce and study a new model for three–dimensional turbulence, the Leray– α model. This model is inspired by the Lagrangian averaged Navier–Stokes– α model of turbulence (also known Navier–Stokes– α model or the viscous Camassa–Holm equations). As in the case of the Lagrangian averaged Navier–Stokes– α model, the Leray– α model compares successfully with empirical data from turbulent channel and pipe flows, for a wide range of Reynolds numbers. We establish here an upper bound for the dimension of the global attractor (the number of degrees of freedom) of the Leray– α model of the order of ( L / l d ) 12/7 , where L is the size of the domain and l d is the dissipation length–scale. This upper bound is much smaller than what one would expect for three–dimensional models, i.e. ( L / l d ) 3 . This remarkable result suggests that the Leray– α model has a great potential to become a good sub–grid–scale large–eddy simulation model of turbulence. We support this observation by studying, analytically and computationally, the energy spectrum and show that in addition to the usual k −5/3 Kolmogorov power law the inertial range has a steeper power–law spectrum for wavenumbers larger than 1/ α . Finally, we propose a Prandtl–like boundary–layer model, induced by the Leray– α model, and show a very good agreement of this model with empirical data for turbulent boundary layers.

Sensing and Manipulation Problems in Endoscopic Surgery: Experiment, Analysis, and Observation

1993 ◽  
Vol 2 (1) ◽  
pp. 66-81 ◽  
Author(s):  
Frank Tendick ◽  
Russell W. Jennings ◽  
Gregory Tharp ◽  
Lawrence Stark
Keyword(s):  
Endoscopic Surgery ◽  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Direct Vision ◽  
Human Hand ◽  
Endoscopic Techniques ◽  
Surgery Patient ◽  
Wide Range ◽  
Recovery Times ◽  
Conventional Open Surgery

The minimally invasive nature of endoscopic surgery allows operations to be performed through small incisions, producing significantly less damage to good tissue than in conventional open surgery. Patient recovery times are thus greatly reduced. This major advantage has driven a dramatic growth of endoscopic techniques in a wide range of surgical applications. Unfortunately, the surgeon's abilities are severely hampered by the limitations of current endoscopic technology. In many ways endoscopic surgery is similar to teleoperation of a remote manipulator. Although the surgeon is physically close to the patient, the surgical environment is effectively “remote,” with sensing and manipulation transmitted through the endoscope and long instruments. Existing solutions from teleoperation applications could likely be applied to endoscopic surgery. This paper attempts to identify the major problems of current endoscopic technology, particularly in vision and manipulation. Vision issues are discussed in the first half, motivated by an experiment comparing surgeons' performance under different visual conditions. Surgeon subjects perform a three-dimensional positioning task with binocular direct vision, monocular direct vision, and a video endoscope. The lack of a stereoscopic view through the endoscope significantly slows performance of the tasks, but there are additional factors that make endoscopic viewing worse than monocular direct viewing. Relevant previous results which demonstrate the significance of interocular spacing in stereo viewing and the effect of display-control axes misalignment are also discussed. Issues of endoscopic manipulation are discussed in the second half of this paper, motivated by a suturing task comparing surgeons' performance with hand and endoscopic instruments. The constraint of endoscopic instruments' passing through the skin reduces their usable degrees of freedom and significantly increases the time to tie a suture knot. Kinematics of endoscopic instruments are compared to the human hand and arm. A model of the surgeon's precision grasp demonstrates the role of stiffness in fine motion control as an example of an advantage of the hand which is lost in the use of endoscopic instruments. The work described in this paper represents an initial effort in identifying problems and evaluating solutions in endoscopic surgery based on objective measurement of performance.

scholarly journals Ultrafast-laser-inscribed 3D integrated photonics: challenges and emerging applications

Nanophotonics ◽  
2015 ◽  
Vol 4 (3) ◽  
pp. 332-352 ◽  
Author(s):  
S. Gross ◽  
M. J. Withford
Keyword(s):  
Degrees Of Freedom ◽  
Three Dimensional ◽  
Laser Pulses ◽  
Femtosecond Laser Pulses ◽  
Ultrafast Laser ◽  
Integrated Photonics ◽  
Transparent Dielectrics ◽  
Wide Range ◽  
The Many ◽  
Quantum Photonics

AbstractSince the discovery that tightly focused femtosecond laser pulses can induce a highly localised and permanent refractive index modification in a large number of transparent dielectrics, the technique of ultrafast laser inscription has received great attention from a wide range of applications. In particular, the capability to create three-dimensional optical waveguide circuits has opened up new opportunities for integrated photonics that would not have been possible with traditional planar fabrication techniques because it enables full access to the many degrees of freedom in a photon. This paper reviews the basic techniques and technological challenges of 3D integrated photonics fabricated using ultrafast laser inscription as well as reviews the most recent progress in the fields of astrophotonics, optical communication, quantum photonics, emulation of quantum systems, optofluidics and sensing.

scholarly journals On the Stability of Reconstruction of Irregularly Sampled Diffraction Fields

2010 ◽  
Vol 2010 ◽  
pp. 1-12
Author(s):  
Vladislav Uzunov ◽  
Atanas Gotchev ◽  
Karen Egiazarian
Keyword(s):  
Degrees Of Freedom ◽  
Light Field ◽  
Monochromatic Light ◽  
Three Dimensional ◽  
Regularized Inversion ◽  
Volume Of Interest ◽  
Wide Range ◽  
Data Points ◽  
Data Point ◽  
The Stability

This paper addresses the problem of reconstruction of a monochromatic light field from data points, irregularly distributed within a volume of interest. Such setting is relevant for a wide range of three-dimensional display and beam shaping applications, which deal with physically inconsistent data. Two finite-dimensional models of monochromatic light fields are used to state the reconstruction problem as regularized matrix inversion. The Tikhonov method, implemented by the iterative algorithm of conjugate gradients, is used for regularization. Estimates of the model dimensionality are related to the number of degrees of freedom of the light field as to show how to control the data redundancy. Experiments demonstrate that various data point distributions lead to ill-poseness and that regularized inversion is able to compensate for the data point inconsistencies with good numerical performance.

scholarly journals Vortex Preconditioning due to Planetary and Gravity Waves prior to Sudden Stratospheric Warmings

2014 ◽  
Vol 71 (11) ◽  
pp. 4028-4054 ◽  
Author(s):  
John R. Albers ◽  
Thomas Birner
Keyword(s):  
Gravity Wave ◽  
Gravity Waves ◽  
Planetary Wave ◽  
Surf Zone ◽  
Polar Vortex ◽  
Wave Drag ◽  
Reanalysis Data ◽  
Composite Analysis ◽  
Large Wave ◽  
Wave Forcing

Abstract Reanalysis data are used to evaluate the evolution of polar vortex geometry, planetary wave drag, and gravity wave drag prior to split versus displacement sudden stratospheric warmings (SSWs). A composite analysis that extends upward to the lower mesosphere reveals that split SSWs are characterized by a transition from a wide, funnel-shaped vortex that is anomalously strong to a vortex that is constrained about the pole and has little vertical tilt. In contrast, displacement SSWs are characterized by a wide, funnel-shaped vortex that is anomalously weak throughout the prewarming period. Moreover, during split SSWs, gravity wave drag is enhanced in the polar night jet, while planetary wave drag is enhanced within the extratropical surf zone. During displacement SSWs, gravity wave drag is anomalously weak throughout the extratropical stratosphere. Using the composite analysis as a guide, a case study of the 2009 SSW is conducted in order to evaluate the roles of planetary and gravity waves for preconditioning the polar vortex in terms of two SSW-triggering scenarios: anomalous planetary wave forcing from the troposphere and resonance due to either internal or external Rossby waves. The results support the view that split SSWs are caused by resonance rather than anomalously large wave forcing. Given these findings, it is suggested that vortex preconditioning, which is traditionally defined in terms of vortex geometries that increase poleward wave focusing, may be better described by wave events (planetary and/or gravity) that “tune” the geometry of the vortex toward its resonant excitation points.

scholarly journals A Possible Influence of Equatorial Winds on the September 2002 Southern Hemisphere Sudden Warming Event

2005 ◽  
Vol 62 (3) ◽  
pp. 651-667 ◽  
Author(s):  
Lesley Gray ◽  
Warwick Norton ◽  
Charlotte Pascoe ◽  
Andrew Charlton
Keyword(s):  
Southern Hemisphere ◽  
Planetary Wave ◽  
Polar Vortex ◽  
Contributory Factor ◽  
Quasi Biennial Oscillation ◽  
Model Studies ◽  
Wave Forcing ◽  
Zonal Winds ◽  
Speed Up ◽  
Biennial Oscillation

Abstract The stratospheric sudden warming in the Southern Hemisphere (SH) in September 2002 was unexpected for two reasons. First, planetary wave activity in the Southern Hemisphere is very weak, and midwinter warmings have never been observed, at least not since observations of the upper stratosphere became regularly available. Second, the warming occurred in a west phase of the quasi-biennial oscillation (QBO) in the lower stratosphere. This is unexpected because warmings are usually considered to be more likely in the east phase of the QBO, when a zero wind line is present in the winter subtropics and hence confines planetary wave propagation to higher latitudes closer to the polar vortex. At first, this evidence suggests that the sudden warming must therefore be simply a result of anomalously strong planetary wave forcing from the troposphere. However, recent model studies have suggested that the midwinter polar vortex may also be sensitive to the equatorial winds in the upper stratosphere, the region dominated by the semiannual oscillation. In this paper, the time series of equatorial zonal winds from two different data sources, the 40-yr ECMWF Re-Analysis (ERA) and the Met Office assimilated dataset, are reviewed. Both suggest that the equatorial winds in the upper stratosphere above 10 hPa were anomalously easterly in 2002. Idealized model experiments are described in which the modeled equatorial winds were relaxed toward these observations for various years to examine whether the anomalous easterlies in 2002 could influence the timing of a warming event. It is found that the 2002 equatorial winds speed up the evolution of a warming event in the model. Therefore, this study suggests that the anomalous easterlies in the 1–10-hPa region may have been a contributory factor in the development of the observed SH warming. However, it is concluded that it is unlikely that the anomalous equatorial winds alone can explain the 2002 warming event.

scholarly journals Climatology and trends in the forcing of the stratospheric zonal-mean flow

2011 ◽  
Vol 11 (4) ◽  
pp. 11649-11690 ◽  
Author(s):  
E. Monier ◽  
B. C. Weare
Keyword(s):  
Planetary Wave ◽  
Polar Vortex ◽  
Wave Activity ◽  
Mean Flow ◽  
Flux Divergence ◽  
Temporal Shift ◽  
Weather Forecasts ◽  
Wave Forcing ◽  
Long Term Changes

Abstract. The momentum budget of the Transformed Eulerian-Mean (TEM) equation is calculated using the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40). This study outlines the considerable contribution of unresolved waves, dominated by gravity waves, to the forcing of the zonal-mean flow. A trend analysis, from 1980 to 2001, shows that the onset and break down of the Northern Hemisphere (NH) stratospheric polar night jet has a tendency to occur later. This temporal shift is associated with long-term changes in the planetary wave activity that are mainly due to synoptic waves. In the Southern Hemisphere (SH), the polar vortex shows a tendency to persist further into the SH summertime. This is associated with a statistically significant decrease in the intensity of the stationary EP flux divergence over the 1980–2001 period. Ozone depletion is well known for strengthening westerly winds through the thermal wind balance, which in turn causes a reduction in wave activity in high latitudes. This study suggests that the decrease in planetary wave activity provides an important feedback to the zonal wind as it delays the breakdown of the polar vortex. Finally, we identify long-term changes in the Brewer-Dobson circulation that, this study suggests, are largely caused by trends in the planetary wave activity during winter and by trends in the gravity wave forcing otherwise.

scholarly journals Linear dynamic properties in curved laminated glasses

2021 ◽  
pp. 44-47
Author(s):  
Olga Sukhanova ◽  
Олексій Ларін
Keyword(s):  
Finite Element ◽  
Degrees Of Freedom ◽  
Dynamic Properties ◽  
Three Dimensional ◽  
Mesh Size ◽  
Polyvinyl Butyral ◽  
Laminated Glass ◽  
Wide Range ◽  
Curvature Parameter ◽  
Work Model

The study presents the results of linear dynamics of laminated glass panels with different curvatures. This is an actual task in the field of mechanical engineering, aviation, shipbuilding, energy, architecture, etc. Such composites are durable, easy to care for and have a wide range of design options. The aim of the work is to study the influence of the curvature parameter on the frequencies and modes of composites. The paper considers the linear characteristics for laminated glass with polyvinyl butyral interlayer. The article considers behavior of the triplex and the propagation of elastic waves in the linear state. The paper performs calculations using the finite element method in the framework of modal analysis in a three-dimensional formulation in the framework of a physical linear-elastic formulation. The study uses hexagonal finite element with 8 nodes with 3 degrees of freedom in each. This work model laminated glass with a curvature parameter ranging from 0 mm to 250 mm. The composite consisted of three layers: two glass layers thickness of each was 3 mm, and a polyvinyl butyral interlayer with 0.38 mm thickness. The size of the plates was 500×500 mm. As a boundary condition, the laminate was fixed on two opposite sides. The article performs mesh size convergence analysis. The results of natural frequencies in accordance with the curvature parameter are derived. The graphs of natural vibration modes are also shown, that give a clear view about the state of composites.

Sign in / Sign up

Export Citation Format

Share Document