Scott A. Elrod

Liveboard: a large interactive display supporting group meetings, presentations, and remote collaboration

This paper describes the Liveboard, a large interactive display system. With nearly one million pixels and an accurate, multi-state, cordless pen, the Liveboard provides a basis for research on user interfaces for group meetings, presentations and remote collaboration. We describe the underlying hardware and software of the Liveboard, along with several software applications that have been developed. In describing the system, we point out the design rationale that was used to make various choices. We present the results of an informal survey of Liveboard users, and describe some of the improvements that have been made in response to user feedback. We conclude with several general observations about the use of large public interactive displays.

Nozzleless droplet formation with focused acoustic beams

We report the use of focused acoustic beams to eject discrete droplets of controlled diameter and velocity from a free‐liquid surface. No nozzles are involved. Droplet formation has been experimentally demonstrated over the frequency range of 5–300 MHz, with corresponding droplet diameters from 300 to 5 μm. The physics of droplet formation is essentially unchanged over this frequency range. For acoustic focusing elements having similar geometries, droplet diameter has been found to scale inversely with the acoustic frequency. A simple model is used to obtain analytical expressions for the key parameters of droplet formation and their scaling with acoustic frequency. Also reported is a more detailed theory which includes the linear propagation of the focused acoustic wave, the coupling of the acoustic fields to the initial surface velocity potential, and the subsequent dynamics of droplet formation. This latter phase is modeled numerically as an incompressible, irrotational process using a boundary integra...

Heterojunction photovoltaic cell

In accordance with one aspect of the present disclosure, a solar photovoltaic device is disclosed. The semiconductor material of the solar photovoltaic device is a heterostructure of two different binary compounds of the same metal. One or both of the two different binary compounds of the same metal are doped so that they have a conduction band edge offset of greater than about 0.4 eV. The binary compound acting as the optical absorbing material of the solar photovoltaic device has a bandgap of about 1.0 eV to about 1.8 eV.Abstract A theoretical evaluation of a heterojunction photovoltaic cell is presented. Short circuit current densities, collection efficiencies, open circuit voltages, and maximum power outputs are calculated and compared to those of equivalent homojunction cells made of the two semiconductor materials forming the heterojunction. The analysis considers the abrupt p - n heterojunction and treats only the case of uniform illumination. Open circuit voltages and short circuit currents, as derived, cannot exceed the values obtained in the equivalent homojunction cells. Cell efficiencies for heterojunctions are thus bounded by the efficiencies of the corresponding homojunctions and any advantages of the cells are limited to those arising out of the window effect (low energy photons pass through one semiconductor to generate carriers in the junction region of the other): i.e., reduced surface recombination losses, and lower sheet resistances.

Acoustic ink printing

An acoustic beam focused on a free liquid surface is used to eject discrete ink droplets of controlled diameter. The liquid surface, adjusted to be at the focal plane of a suitable focusing element, is excited with a burst of acoustic energy. Spherical lead zirconate titanate (PZT) shells, acoustic microscope lenses, spherical lenses etched in silicon, and Fresnel acoustic lenses are used successfully to eject droplets. Droplet diameter scales directly with the focal spot size, and inversely with the acoustic frequency. Droplet formation is experimentally demonstrated over the frequency range of 5 to 300 MHz, with corresponding droplet diameters from 300 to 5 mu m. This droplet ejection process is successfully utilized for a printing application by using ink as the liquid medium. Acoustic ink printing with a single lens and with an array of lenses is described.<<ETX>>

Ultra-High-Throughput Microarray Generation and Liquid Dispensing Using Multiple Disposable Piezoelectric Ejectors

The authors have constructed an array of 12 piezoelectric ejectors for printing biological materials. A single-ejector footprint is 8 mm in diameter, standing 4 mm high with 2 reservoirs totaling 76 µL. These ejectors have been tested by dispensing various fluids in several environmental conditions. Reliable drop ejection can be expected in both humidity-controlled and ambient environments over extended periods of time and in hot and cold room temperatures. In a prototype system, 12 ejectors are arranged in a rack, together with an X - Y stage, to allow printing any pattern desired. Printed arrays of features are created with a biological solution containing bovine serum albumin conjugated oligonucleotides, dye, and salty buffer. This ejector system is designed for the ultra-high-throughput generation of arrays on a variety of surfaces. These single or racked ejectors could be used as long-term storage vessels for materials such as small molecules, nucleic acids, proteins, or cell libraries, which would allow for efficient preprogrammed selection of individual clones and greatly reduce the chance of cross-contamination and loss due to transfer. A new generation of design ideas includes plastic injection molded ejectors that are inexpensive and disposable and handheld personal pipettes for liquid transfer in the nanoliter regime. (Journal of Biomolecular Screening 2004:85-94)

Hot melt ink acoustic printing

To facilitate the use of hot melt inks in acoustic ink printers of the type having a printhead including one or more acoustic droplet ejectors for supplying focused acoustic beams, such a printer comprises a carrier for transporting a generally uniformly thick film of hot melt ink across its printhead, together with a heating means for liquefying the ink as it nears the printhead. The droplet ejector or ejectors are acoustically coupled to the ink via the carrier, and their output focal plane is essentially coplanar with the free surface of the liquefied ink, thereby enabling them to eject individual droplets of ink therefrom on command. The ink, on the other hand, is moved across the printhead at a sufficiently high rate to maintain the free surface which it presents to the printhead at a substantially constant level. A variety of carriers may be employed, including thin plastic and metallic belts and webs, and the free surface of the ink may be completely exposed or it may be partially covered by a mesh or perforated layer. A separate heating element may be provided for liquefying the ink, or the lower surface of the carrier may be coated with a thin layer of electrically resistive material for liquefying the ink by localized resistive heating.

A Nano-Cellular Local Area Network Using Near-Field RF Coupling

This paper describes a new type of wireless LAN based on near-field RF coupling. The system exploits the rapid spatial decay of field strength within the near-field to provide high isolation between adjacent cells. We believe that this Nano-Cellular system offers unique advantages for mobile computing in an indoor environment. At the operating frequency of 5.3 MHz, the cell size is approximately that of a single office. Small cells offer several benefits, including the possibility of channel re-use and the ability to provide information about user location. Despite the low operating frequency, the available bit rate of 250kbps is sufficient for many practical applications. The radio wavelength of 60m is sufficiently long to eliminate standing wave problems which often plague indoor UHF and microwave systems. The transceiver uses very little power, and has a simple, low-cost design.

Focused acoustic beams for nozzleless droplet formation

The authors report the use of focused acoustic beams to eject discrete droplets of controlled diameter and velocity from a free liquid surface. No nozzles are involved. Droplet formation has been experimentally demonstrated over the frequency range 5 to 300 MHz, with corresponding droplet diameters from 300 to 5 mu m. The physics of droplet formation is essentially unchanged over this frequency range. For acoustic focusing elements have similar geometries, droplet diameter has been found to scale inversely with the acoustic frequency. The authors summarize the results of a simple model that is used to obtain analytical expressions for important parameters and their scaling with acoustic frequency. The authors also briefly describe a numerical model that successfully predicts the key features of droplet formation.<<ETX>>