The NSF Digital Clay project is focused on the design, prototyping, integration, and validation of a computercontrolled physical device capable of taking any of a wide range of possible shapes in response to changes in a digital 3D model or to changes in the pressure exercised upon it by human hands. Although it clearly is a natural and unavoidable evolution of 3D graphical user interfaces, its unprecedented capabilities constitute a major leap in technologies and paradigms for 3D display, for 3D input, and for collaborative 3D design. In this paper, we provide an overview of the Digital Clay project and discuss the challenges, design choices, and initial solutions for a new Finger Sculpting interface designed for the Digital Clay and prototyped using conventional 3D I/O hardware.

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The Algorithm of Mode Isolation ͑AMI͒ is an iterative procedure for identifying the number of modes contributing to a frequency response function ͑FRF͒ concurrently with identifying the complex eigenvalues and eigenvectors of those modes. The latest modifications obtain these modal properties solely by using linear least squares fits of the FRF data to canonical forms. The algorithmic operations are explained in a detailed sequence of steps that are illustrated by some sample data. The computational efficiency of AMI relative to other modal identification algorithms that fit response data to multi-degree-of-freedom model equations is discussed.

Controlling biological processes using light has increased the accuracy and speed with which researchers can manipulate many biological processes. Optical control allows for an unprecedented ability to dissect function and holds the potential for enabling novel genetic therapies. However, optogenetic experiments require adequate light sources with spatial, temporal, or intensity control, often a bottleneck for researchers.Here we detail how to build a low-cost and versatile LED illumination system that is easily customizable for different available optogenetic tools. This system is configurable for manual or computer control with adjustable LED intensity. We provide an illustrated step-by-step guide for building the circuit, making it computer-controlled, and constructing the LEDs. To facilitate the assembly of this device, we also discuss some basic soldering techniques and explain the circuitry used to control the LEDs.Using our open-source user interface, users can automate precise timing and pulsing of light on a personal computer (PC) or an inexpensive tablet. This automation makes the system useful for experiments that use LEDs to control genes, signaling pathways, and other cellular activities that span large time scales. For this protocol, no prior expertise in electronics is required to build all the parts needed or to use the illumination system to perform optogenetic experiments.

The algorithm of mode isolation is a frequency domain method for processing measured response data in order to identify the modal properties of a system. It has been shown [M. V. Drexel and J. H. Ginsberg, Proceedings of the 19th IMAC, Orlando, FL, 5–8 February 2001] to accurately evaluate a pair of damped modes whose natural frequencies differ by an amount that is commensurate with the bandwidth of either mode. Here, SIMO measurement of a two-degree-of-freedom system is simulated analytically by adding white noise to the computed response. This system is selected because the natural frequency difference can be made as small as desired by adjusting a parameter that has little effect on the modal damping ratios in the range of interest. Analytically, the two normal modes are unique and mutually orthogonal if the frequency difference is nonzero, while repeated frequencies lead to two arbitrary, and not necessarily mutually orthogonal, modes. The present work explores the degree to which AMI tracks the analytical behavior, specifically, its ability to detect and characterize the modes with decreasing frequency difference.