Plateau Tank Apparatus for The Study of Liquid Bridges

An apparatus has been constructed and used to study the equilibrium and dynamical behavior of liquid bridges under reduced effective gravity. Liquid bridges are created and manipulated using six independent computer controlled stepper motors which drive linear motion tables. The bridges are visualized with a high magnification coherent Fourier optical system and in an orthogonal view using incoherent white light. By calibrating a density hydrometer and measuring the interfacial energy between the bridge and bath, reliable Bond numbers as low as 10−4 can be created and held stable for extended periods of time. Dimensional control of the liquid bridges approaches one part in 10−4 for the aspect ratio and volume. The apparatus has been tested by measuring the static stability limits of axisymmetric bridges and comparing the results with previous theoretical predictions. Experimental error for the apparatus is δBo/Bo=0.03, δΛ/Λ=0.001 and δV/V =0.001, where Bo is the Bond number, Λ is the aspect ratio of the bridge, and V is the dimensionless (relative) volume of the bridge

RAFCON: a Graphical Tool for Task Programming and Mission Control

There are many application fields for robotic systems including service robotics, search and rescue missions, industry and space robotics. As the scenarios in these areas grow more and more complex, there is a high demand for powerful tools to efficiently program heterogeneous robotic systems. Therefore, we created RAFCON, a graphical tool to develop robotic tasks and to be used for mission control by remotely monitoring the execution of the tasks. To define the tasks, we use state machines which support hierarchies and concurrency. Together with a library concept, even complex scenarios can be handled gracefully. RAFCON supports sophisticated debugging functionality and tightly integrates error handling and recovery mechanisms. A GUI with a powerful state machine editor makes intuitive, visual programming and fast prototyping possible. We demonstrated the capabilities of our tool in the SpaceBotCamp national robotic competition, in which our mobile robot solved all exploration and assembly challenges fully autonomously. It is therefore also a promising tool for various RoboCup leagues.Comment: 8 pages, 5 figure

Method for fabricating a low stress x-ray mask using annealable amorphous refractory compounds

X‐ray masks have been fabricated by depositing a compressively stressed refractory material on a wafer, annealing to a zero stress state, and then forming the membrane. Amorphous TaSiN and TaSi alloys deposited with a magnetron sputter tool have been extensively characterized in terms of resistivity, composition, defectivity, surface roughness, and crystalline state. Optimization in terms of these parameters has resulted in base line selection of absorber films of the following compositions: Ta_(61)Si_(17)N_(21) and Ta_(75)Si_(23). The process is shown to be extendable to an entire class of amorphous annealable refractory materials. Careful studies of deposition and annealing conditions have resulted in a 4× reduction of image placement to the 30 nm maximum vector level. Finally, the importance of stress gradients is experimentally verified

Dips in Partial Wave Amplitudes from Final State Interactions

We consider the dip-peak structures in the J=0 partial wave amplitudes for processes \gamma\gamma\rightarrow W^+W^-~ \mbox{and}~\gamma\gamma,gg\rightarrow t\overline{t} taking into account the corresponding Born term process and the rescattering process where the intermediate state is rescattered through the exchange of Higgs resonance state in the direct channel.Comment: 9 pages, CPP-93-21, 6 figures not include

Bifurcation of The Equilibrium States of A Weightless Liquid Bridge

The bifurcation of the solutions of the nonlinear equilibrium problem of a weightless liquid bridge with a free surface pinned to the edges of two coaxial equidimensional circular disks is examined. The bifurcation is studied in the neighborhood of the stability boundary for axisymmetric equilibrium states with emphasis on the boundary segment corresponding to nonaxisymmetric critical perturbations. The first approximations for the shapes of the bifurcated equilibrium surfaces are obtained. The stability of the bifurcated states is then determined from the bifurcation structure. Along the maximum volume stability limit, depending on values of the system parameters, loss of stability with respect to nonaxisymmetric perturbations results in either a jump or a continuous transition to stable nonaxisymmetric shapes. The value of the slenderness at which a change in the type of transition occurs is found to be Λs=0.4946. Experimental investigation based on a neutral buoyancy technique agrees with this prediction. It shows that, for Λ\u3cΛs, the jump is finite and that a critical bridge undergoes a finite deformation to a stable nonaxisymmetric state

Bifurcation of The Equilibrium States of A Weightless Liquid Bridge

The bifurcation of the solutions of the nonlinear equilibrium problem of a weightless liquid bridge with a free surface pinned to the edges of two coaxial equidimensional circular disks is examined. The bifurcation is studied in the neighborhood of the stability boundary for axisymmetric equilibrium states with emphasis on the boundary segment corresponding to nonaxisymmetric critical perturbations. The first approximations for the shapes of the bifurcated equilibrium surfaces are obtained. The stability of the bifurcated states is then determined from the bifurcation structure. Along the maximum volume stability limit, depending on values of the system parameters, loss of stability with respect to nonaxisymmetric perturbations results in either a jump or a continuous transition to stable nonaxisymmetric shapes. The value of the slenderness at which a change in the type of transition occurs is found to be Λs=0.4946. Experimental investigation based on a neutral buoyancy technique agrees with this prediction. It shows that, for Λ\u3cΛs, the jump is finite and that a critical bridge undergoes a finite deformation to a stable nonaxisymmetric state

The cubic period-distance relation for the Kater reversible pendulum

We describe the correct cubic relation between the mass configuration of a Kater reversible pendulum and its period of oscillation. From an analysis of its solutions we conclude that there could be as many as three distinct mass configurations for which the periods of small oscillations about the two pivots of the pendulum have the same value. We also discuss a real compound Kater pendulum that realizes this property.Comment: 25 pages 4figure

Moments of inertia for solids of revolution and variational methods

We present some formulae for the moments of inertia of homogeneous solids of revolution in terms of the functions that generate the solids. The development of these expressions exploits the cylindrical symmetry of these objects, and avoids the explicit use of multiple integration, providing an easy and pedagogical approach. The explicit use of the functions that generate the solid gives the possibility of writing the moment of inertia as a functional, which in turn allows us to utilize the calculus of variations to obtain a new insight into some properties of this fundamental quantity. In particular, minimization of moments of inertia under certain restrictions is possible by using variational methods.Comment: 6 pages, 6 figures, LaTeX2e. Two paragraphs added. Minor typos corrected. Version to appear in European Journal of Physic

Detecting a conditional extrme value model

In classical extreme value theory probabilities of extreme events are estimated assuming all the components of a random vector to be in a domain of attraction of an extreme value distribution. In contrast, the conditional extreme value model assumes a domain of attraction condition on a sub-collection of the components of a multivariate random vector. This model has been studied in \cite{heffernan:tawn:2004,heffernan:resnick:2007,das:resnick:2008a}. In this paper we propose three statistics which act as tools to detect this model in a bivariate set-up. In addition, the proposed statistics also help to distinguish between two forms of the limit measure that is obtained in the model.Comment: 21 pages, 4 figure

Dynamics and statics of nonaxisymmetric liquid bridges

We finished the construction of the experimental apparatus and the design and testing of some of the visualization and data acquisition techniques. Experimental work focused on three areas: force measurements, loss of stability to nonaxisymmetric bridges, and vibration behavior. The experimental work is summarized in section 2. Selected results from our force measurement experiments are outlined in section 3. In addition we worked on the theory of the dynamic stability of axisymmetric bridges and undertook numerical simulation of the effects of inclined gravity vectors on the minimum volume stability limit for static bridges. The results and status of our theoretical work and numerical simulation are described in section 4. Papers published and in preparation, conference presentations, etc., are described in section 5. Work planned for the third year is discussed in section 6. References cited in the report are listed in section 7