Robert Pastel

Particle manipulation and surface patterning by laser guidance

Laser-induced forces are used to manipulate atoms, clusters, and micron-sized particles in hollow optical fibers. Laser light (400 mW, 800 nm) is guided in a low-order grazing incidence mode in glass capillaries. The optical field in the fiber generates gradient and scattering forces which simultaneously draw particles to the center of the hollow region and push them along the fiber axis. Dielectric, semiconductor, and metal particles in the size range of 9 μm–50 nm have been guided in gas- and liquid-filled fibers. Rb atoms are guided in evacuated fiber for up to 15 cm. Used alone or in conjunction with traditional methods, laser guidance is attractive for direct-write lithography. Arbitrary surface patterns can be created under ambient conditions with potential write speeds exceeding 106 particles/s and placement accuracy approaching 50 nm (assuming a 1 W laser, 100 nm Ge particles, and fiber filled with Ar at 760 Torr). Anisotropic optical forces resulting from particle shape anisotropy act to orient p...

Measuring the difficulty of steering through corners

The steering law is intended to predict the performance of cursor manipulations in user interfaces, but the law has been verified for only a few path shapes and should be verified for more if it is to be generalized. This study extends the steering law to paths with corners. Two experiments compare the movement times of negotiating paths with corners to straight paths with the same width and movement amplitude. The experimental results show a significant effect on the movement times due to the corners, extending far into the legs of the paths corner. Modeling the results using resource theory, a cognitive theory for divided attention, suggests that steering through corners is two simultaneous tasks: steering along the legs of the corner and aiming at the corner.

Laser trapping of microscopic particles for undergraduate experiments

We present detailed instructions for constructing and operating an optical trap using a hollow core fiber and two-laser beams. The trap is stable, confining 100-nm to 10-μm particles of a variety of materials for hours of leisurely observation. The trap operates at room temperature and atmospheric pressure, costs less than

Integrating science and research in a HCI design course

1400, and requires no machining. The hollow fiber provides automatic relative beam alignment and shields trapped particles from the ambient convective flow. An experiment and analysis of the Mie scattering from the trapped particle is outlined. A list of other interesting experiments based on the trap is provided.

Combining distinct graduate and undergraduate HCI courses: an experiential and interactive approach

Undergraduate computer science students have few opportunities to experience scientific investigation and computer science research. A human-computer interaction (HCI) course can offer many opportunities for research that are accessible to undergraduate students, and because of the similarity between the design and research processes, a design project based HCI course is particularly suited to introducing undergraduate computer science students to the research process. In this paper, we describe and discuss the challenges of integrating research projects into a design HCI course. We also present example research projects and discuss the feedback form students attending the course.

Demonstrating information in simple gestures

We developed combined graduate and undergraduate courses in which undergraduates created a prototype based on user-centered design, and graduate students worked with them to evaluate those prototypes based on common usability principles. It provided undergraduate students experience practicing user centered design, while providing graduate students experience with usability evaluation. It also provided graduate students the opportunity to introduce current HCI research areas to students who may be considering graduate school. The course successfully engaged both graduate and undergraduate students while providing a beneficial experience through their interactions.

Positioning graphical objects on computer screens: a three-phase model.

We introduce the simple gesturing user interface (SGUI), an application programming interface (API) for designing user interfaces utilizing simple gesturing on the personal digital assistant (PDA). SGUI is particularly appropriate for PDA interfaces because the simple gestures are recognized using minimum processing power and reserve all of the small display for user-task specific information. A graphing-software implemented on a PDA using SGUI illustrates the usability of gesturing interfaces and the information conveyed in a single gesture stroke.

Measuring evaporation rates of laser-trapped droplets by use of fluorescent morphology-dependent resonances

Objective: This experiment identifies and models phases during the positioning of graphical objects (called cursors in this article) on computer displays. Background: The human computer-interaction community has traditionally used Fitts’ law to model selection in graphical user interfaces, whereas human factors experiments have found the single-component Fitts’ law inadequate to model positioning of real objects. Method: Participants (N = 145) repeatedly positioned variably sized square cursors within variably sized rectangular targets using computer mice. The times for the cursor to just touch the target, for the cursor to enter the target, and for participants to indicate positioning completion were observed. The positioning tolerances were varied from very precise and difficult to imprecise and easy. Results: The time for the cursor to touch the target was proportional to the initial cursor-target distance. The time for the cursor to completely enter the target after touching was proportional to the logarithms of cursor size divided by target tolerances. The time for participants to indicate positioning after entering was inversely proportional to the tolerance. Conclusions: A three-phase model defined by regions—distant, proximate, and inside the target—was proposed and could model the positioning tasks. Applications: The three-phase model provides a framework for ergonomists to evaluate new positioning techniques and can explain their deficiencies. The model provides a means to analyze tasks and enhance interaction during positioning.

JUG: a JUnit generation, time complexity analysis and reporting tool to streamline grading

Morphology-dependent resonances (MDRs) are used to measure accurately the evaporation rates of laser-trapped 1- to 2-mum droplets of ethylene glycol. Droplets containing 3 x 10(-5) M Rhodamine-590 laser dye are optically trapped in a 20-mum hollow fiber by two counterpropagating 150-mW, 800-nm laser beams. A weaker 532-nm laser excites the dye, and fluorescence emission is observed near 560 nm as the droplet evaporates. A complete series of first-order TE and TM MDRs dominates the fluorescent output. MDR mode identification sizes the droplets and provides accurate evaporation rates. We verify the automated MDR mode identification by counting fringes in a videotape of the experiment. The longitudinal spring constant of the trap, measured by analysis of the videotaped motion of droplets perturbed from the trap center, provides independent verification of the lasers intensity within the trap.

A Case Study in Canine-Human Factors: A Remote Scent Sampler for Landmine Detection

The JUnit Generation (JUG) system provides fast, semiautomated feedback to students. It uses a Java-like script to generate unit tests and time complexity tests, then runs those tests to generate reports. The goals for JUG are improved feedback for students, and decreased preparation and grading time for instructors and grading assistants.