Adam Seeger

VRPN: a device-independent, network-transparent VR peripheral system

The Virtual-Reality Peripheral Network (VRPN) system provides a device-independent and network-transparent interface to virtual-reality peripherals. VRPNs application of factoring by function and of layering in the context of devices produces an interface that is novel and powerful. VRPN also integrates a wide range of known advanced techniques into a publicly-available system. These techniques benefit both direct VRPN users and those who implement other applications that make use of VR peripherals.

In situ resistance measurements of strained carbon nanotubes

We investigate the response of multiwalled carbon nanotubes to mechanical strain applied with an atomic force microscope probe. We find in some samples, changes in the contact resistance dominate the measured resistance change. In others, strain large enough to fracture the tube can be applied without a significant change in the contact resistance. In this case, we observe that enough force is applied to break the tube without any change in resistance until the tube fails. We have also manipulated the ends of the broken tube back in contact with each other, re-establishing a finite resistance. We observe that, in this broken configuration, the resistance of the sample is tunable to values 15–350 kΩ greater than prior to breaking.

Controlled placement of an individual carbon nanotube onto a microelectromechanical structure

We report on the precise placement of a single carbon nanotube (CNT) onto a microlectromechanial system (MEMS) structure. Using a hybrid atomic force microscope/scanning electron microscope (AFM/SEM) system, an individual multiwalled CNT was retrieved from a cartridge by the AFM tip, translated to a MEMS device, and then placed across a gap between an actuating and a stationary structure. Progress toward a resistance versus stress/strain measurement on a CNT will be discussed, including SEM images of a MEMS structure we have designed specifically for such a measurement.

Mechanical and optical manipulation of porphyrin rings at the submicrometre scale

Scanning probe microscopes (SPMs) and especially the atomic force microscope (AFM) can be used as tools for modifying surface structures on the submicrometre and even nanometre scale. For this purpose an advanced interface has been developed to facilitate these manipulations and greatly increase the number of possible applications. In this paper this interface (the nanoManipulator, developed at the University of North Carolina at Chapel Hill) is implemented on a combined AFM-confocal microscope. This setup allows AFM imaging, manipulations and fluorescence imaging of the same area on the sample. The new setup is tested on ringlike structures of a porphyrin derivative (BP6). A small amount of the fluorescent material could be displaced with the AFM tip. A special tool (sweep mode) allowed a modification of around 130 nm, which was afterwards detectable with the confocal microscope. The resolution attainable in these kind of experiments could go down below 100 nm and is primarily determined by the tip and sample geometry. Comparable with this experiment is the application of a near-field scanning optical microscope (NSOM) to make photochemical modifications. Using the excitation power coming from the NSOM probe the fluorescence can be quenched by bleaching a selected area instead of displacing the material. Application on the BP6 rings led to a modification of 280 nm wide. AFM can perform modifications on a smaller scale but is less selective than NSOM. Optical investigation of the changes after AFM manipulation can give more elaborate information on the modifications. This will extend the possible applications of the techniques and may ultimately go down to the single-molecule level.

Factors contributing to the integration of textural qualities: Evidence from virtual surfaces

Two experiments involving indirect touch were carried out to explore the relationships among perceptual dimensions of haptically examined surfaces. Subjects in both experiments used a stylus to evaluate the properties of virtual surfaces created by a force-feedback device; four surface properties (resistance to normal force, coefficient of friction, texture scale, and vibration amplitude) were manipulated in various combinations. In Experiment 1, the extent to which there was a one-to-one relationship between specific stimulus properties and perceptual qualities (“perceptual separability”) was evaluated. A substantial failure of separability was demonstrated, with friction tending to be more separable from the other properties than they were from one another. The pattern of results suggests that the amount of measured separability depends crucially on the way stimulus properties are defined (e.g., force versus displacement). In Experiment 2, surfaces with known perceptual properties were used to study the metric(s) of the relevant perceptual space. By specifying the perceptual, rather than the stimulus, coordinates of the surfaces, it was possible to bypass issues of perceptual separability. For surfaces of equal friction, a Euclidean metric captured the results (r2 = 0.75) more effectively than a city-block metric did; neither metric did well when differences in friction were involved. The fact that—unlike stickiness—hardness, roughness, and perceived vibration intensity are all increasing functions of surface-normal forces may facilitate their integration into a Euclidean space, in both direct (Hollins M, Bensmaïa S, Karlof K, Young F, . Individual differences in perceptual space for tactile textures: Evidence from multidimensional scaling. Percept Psychophys 62:1534–1544.) and indirect touch.

Haptic Perception of Virtual Surfaces: Scaling Subjective Qualities and Interstimulus Differences

We examined, in two experiments, the perceptual scaling of the properties of haptically examined virtual surfaces, and the way in which these properties subjectively combine. Participants used a consistent movement pattern to explore, with a stylus, virtual surfaces generated by a force-feedback device. In experiment 1, four surface properties (bump size, friction, resistance to normal force, and vibration amplitude) were varied individually, in separate blocks of trials. Free magnitude estimates of the subjective dimensions corresponding to these properties showed that all four dimensions conformed closely to the power law, except at very low stimulus values. Exponents for bump size (0.80) and stiffness (1.01) were consistent with values established in earlier work with direct touch of real surfaces. Surprisingly, the exponent for stickiness, not previously measured, was much higher than those for other dimensions (1.49). In experiment 2, dimensional combinations were analyzed by asking subjects to give magnitude estimates of the subjective difference between pairs of surfaces differing in one or two properties. Magnitude estimates of a given one-dimensional difference were generally larger when the subject was pressing down firmly on the surfaces, than when only gentle downward pressure was required; this result suggests that forces generated when a surface is haptically examined are interpreted as invariant indicators of the magnitudes of the surface properties themselves. Estimates of one-dimensional differences were also used to make predictions of two-dimensional differences, under assumptions of dimensional integrality and separability. The results fell between these two sets of predictions, indicating only modest integration of surface properties examined with indirect touch.

Hands-on tools for nanotechnology

We describe some mechanical and electrical measurements on carbon nanotubes. We discuss electron beam lithography techniques to form metal wire contacts to the as-found nanometer structures. Starting from a unique collaborative perspective, we suggest some improved design and alignment methods.

Visualization and natural control systems for microscopy

This chapter presents these microscope systems, along with brief descriptions of the science experiments driving the development of each system. Beginning with a discussion of the philosophy that has driven the Nanoscale Science Research Group (NSRG) and the methods used, the chapter describes the lessons learned during system development, including both useful directions and blind alleys. The first lesson is to begin software development at least as soon as hardware development. The second lesson is to partner with experts in required technologies. The NSRG attempts to use the best available computer technology to develop effective systems for use by the physical science team, which then become cost-effective and can be deployed on widely available hardware as technology marches on. The chapter also describes techniques to enable telemicroscopy in the context of remote experiments and outreach.