Constraint-based synthesis of shape-morphing compliant structures in virtual reality

The purpose of this research is to establish a novel approach to the design of compliant shape-morphing structures using constraint-based design methods (CBDM) and virtual reality (VR). Compliant mechanisms, as opposed to rigid link mechanisms, achieve motion guidance via the compliance and deformation of the mechanism\u27s members. They are currently being explored as structural components to produce shape changes in products such as aircraft wing and antenna reflectors. The goal is to design a single-piece flexible structure capable of morphing a given curve or profile into a target curve or profile while utilizing the minimum number of actuators. The successful design of compliant mechanisms requires an understanding of solid mechanics (deformation, stress, strain, etc.) and mechanism kinematics (properties of motion). As a result, only a fairly narrow, experienced group of engineers are successful in designing these mechanisms. This approach was developed as an alternative to the two primary methods prevalent in the design community at this time - the pseudo-rigid body method (PRBM) and the topological synthesis (which tend to suffer from either a poor potential solution synthesis capabilities or from susceptibility to overly-complex solutions). A tiered design method that relies on kinematics, finite element analysis, and optimization in order to apply the CBDM concepts to the design and analysis of shape-morphing compliant structures is presented. By segmenting the flexible element that comprises the active shape surface at multiple points in both the initial and the target configurations and treating the resulting individual elements as rigid bodies that undergo a planar or general spatial displacement we are able to apply the traditional kinematics theory to rapidly generate sets of potential solutions. An FEA-augmented optimization sequence establishes the final compliant design candidate. Coupled with a virtual reality interface and a force-feedback device this approach provides the ability to quickly specify and evaluate multiple design problems in order to arrive at the desired solution without an excessive number of design iterations and a heavy dependence on the intermediate physical prototypes

Back gating of a two-dimensional hole gas in a SiGe quantum well

A device comprising a low-resistivity, n-type, Si substrate as a back gate to a p-type (boron), remote-doped, SiGe quantum well has been fabricated and characterized. Reverse and forward voltage biasing of the gate with respect to the two-dimensional hole gas in the quantum well allows the density of holes to be varied from 8 × 1011 cm–2 down to a measurement-limited value of 4 × 1011 cm–2. This device is used to demonstrate the evolution with decreasing carrier density of a re-entrant insulator state between the integer quantum Hall effect states with filling factors 1 and 3

Spin-orbit-induced correlations of the local density of states in two-dimensional electron gas

We study the local density of states (LDOS) of two-dimensional electrons in the presence of spin-orbit (SO) coupling. Although SO coupling has no effect on the average density of states, it manifests itself in the correlations of the LDOS. Namely, the correlation function acquires two satellites centered at energy difference equal to the SO splitting, $2\omega_{SO}$, of the electron Fermi surface. For a smooth disorder the satellites are well separated from the main peak. Weak Zeeman splitting $\omega_{Z} \ll \omega_{SO}$ in a parallel magnetic field causes an anomaly in the shape of the satellites. We consider the effect of SO-induced satellites in the LDOS correlations on the shape of the correlation function of resonant-tunneling conductances at different source-drain biases, which can be measured experimentally. This shape is strongly sensitive to the relation between $\omega_{SO}$ and $\omega_{Z}$.Comment: 10 pages, 4 figure

Microwave induced magnetoresistance oscillations at the subharmonics of the cyclotron resonance

The magnetoresistance oscillations, which occur in a two-dimensional electron system exposed to strong microwave radiation when the microwave frequency $\omega$ coincides with the n-th subharmonic of the cyclotron frequency $\omega_c$ have been investigated for n = 2, 3 and 4. It is shown that these subharmonic features can be explained within a non-equilibrium energy distribution function picture without invoking multi-photon absorption processes. The existence of a frequency threshold above which such oscillations disappear lends further support to this explanation.Comment: 5 pages, 5 figure

Oscillatory nonlinear differential magnetoresistance of highly mobile 2D electrons in high Landau levels

We examine the current-induced magnetoresistance oscillations in high-mobility two-dimensional electron systems using the balance-equation scheme for nonlinear magnetotransort. The reported analytical expressions for differential magnetoresistivity at high filling factors in the overlapping Landau-level regime, which show good agreement with the experimental observation and the numerical calculation, may be helpful in extracting physical information from experiments.Comment: 4 pages, 2 figure

Microwave photoresponse in the 2D electron system caused by intra-Landau level transitions

The influence of microwave radiation on the DC-magnetoresistance of 2D-electrons is studied in the regime beyond the recently discovered zero resistance states when the cyclotron frequency exceeds the radiation frequency. Radiation below 30 GHz causes a strong suppression of the resistance over a wide magnetic field range, whereas higher frequencies produce a non-monotonic behavior in the damping of the Shubnikov-de Haas oscillations. These observations are explained by the creation of a non-equilibrium electron distribution function by microwave induced intra-Landau level transitions.Comment: 4 pages, 5 figure

Fractional quantum Hall effect without energy gap

In the fractional quantum Hall effect regime we measure diagonal ($\rho_{xx}$) and Hall ($\rho_{xy}$) magnetoresistivity tensor components of two-dimensional electron system (2DES) in gated GaAs/Al$_{x}$Ga$_{1-x}$As heterojunctions, together with capacitance between 2DES and the gate. We observe 1/3- and 2/3-fractional quantum Hall effect at rather low magnetic fields where corresponding fractional minima in the thermodynamical density of states have already disappeared manifesting complete suppression of the quasiparticle energy gaps.Comment: 4 pages, 4 figure

Implementing Speech Recognition in Virtual Reality

Virtual Reality (VR) is becoming an important tool in the engineering product development process. The virtual environment provides the user with the ability to interact with three-dimensional digital representations of products using natural head and hand motions. While interacting with digital objects in VR seems natural, the use of traditional two-dimensional menu systems does not always provide a convenient interface to controlling task specifications in the three-dimensional space. New human-computer-interfaces are needed for this emerging VR design tool. This paper will present the details of implementing a speaker-independent, command and control, speech recognition menuing system for a virtual reality application. The menuing system will be described as it is incorporated into a virtual environment for the design of spatial mechanisms. Design and technical issues involved in the interface creation process are discussed and the resulting interaction system is described