Towards automatic evaluation of multimodal user interfaces

The evaluation of the usability and the learnability of a computer system may be performed with predictive models during the design phase. It may be done on the executable code as well as by observing the user in action. In the latter case, data collected in vivo must be processed. The goal is to provide software supports for performing this difficult and time consuming task.

The paper presents an early analysis of, and experience relating to, the automatic evaluation of multimodal user interfaces. With this end in view, a generic Wizard of Oz platform has been designed to allow the observation and automatic recording of subjects' behavior while they interact with a multimodal interface. It is then shown how recorded data can be analyzed to detect behavioral patterns, and how deviations of such patterns from a data-flow-oriented task model can be exploited by a software usability critic.     

Analytical modeling and optimization of terahertz time-domainspectroscopy experiments, using photoswitches as antennas

From classical charge transport equations and dipole radiation equations, we derive a simple analytical model for the signal detected in terahertz time-domain spectroscopy using photoconducting antennas. The validity of our model is checked by comparison to published calculated results and to experimental data we have measured. This expression depends mostly on the carrier lifetime in the antennas' semiconductor material and on the laser pulse duration. The analytical form of the detected terahertz (THz) signal allows us to separate the contribution of the different experimental parameters. Together with a detailed noise analysis in THz time-domain spectroscopy, we optimize the parameter values in order to achieve the largest dynamics of measurement     

Study of Optoelectronic Sampler Linearity for Analog-to-Digital Conversion of RF Signals

Photoconductive sampling of 10-GHz radio- frequency (RF) signal is demonstrated using interdigitated photoswitches made from low-temperature grown GaAs. We study the linearity of the device for RF input power ranging from -3 to 20 dBm. For moderate levels, the sampler shows a spurious-free dynamic range (SFDR) better than 40 dB. For the largest values, it exhibits a nonlinear response that deteriorates both SFDR and resolution. This nonlinearity is attributed to drift velocity saturation in the semiconductor material.     

Grating-assisted coupling of terahertz waves into a dielectric waveguide studied by terahertz time-domain spectroscopy

We report on the efficient coupling of terahertz (THz) waves into a dielectric waveguide by means of a diffraction grating engraved at the top of the waveguide. The waveguide is made of a 201-microm-thick high-resistivity silicon wafer. The transmission of the device, measured versus frequency by terahertz time-domain spectroscopy, shows usual m lines when a frequency component of the THz pulse spectrum satisfies the phase-matching condition and is coupled into the waveguide. The experimental data are well modeled with the differential electromagnetic method to compute the diffraction pattern of the grating device. The dispersion curve of the first four modes of propagation is determined from the frequency position of the m lines recorded for different angles of incidence of the THz beam. The waveguide exhibits a weak group velocity dispersion at high frequencies.     

THz Spectroscopy Using Low Temperature Mesoscopic Devices

The prototype of a THz spectroscopic camera based on low temperature mesoscopic devices is presented. The core of this system is an array of Quantum-Dots coupled to Quantum Point Contact sensors. Readout electronics is based on Time Domain Multiplexing combined with Lock-in technique. Results show that such system can reach the sensitivity needed to detect THz emission of materials in a fully passive way.     

Grating-enhanced second-harmonic generation in polymer waveguides: role of losses

A numerical study of second-harmonic (SH) generation in a corrugated polymer waveguide is performed with a rigorous electromagnetic theory. Comparison with experiment reveals the role of losses inside the waveguide-small losses do not significantly affect the nonresonant response and reduce the resonant enhancement of SH generation. High losses can lead to the opposite effect-instead of enhancement, dips in the SH efficiency are observed in the vicinity of guided-wave excitation. The peculiarities of the angular dependencies of SH generation are explained from the phenomenological point of view, and the role of phase matching is discussed.     

Terahertz Generation by Optical Rectification in Sugar Crystal

Journal of Infrared, Millimeter, and Terahertz Waves - We report on THz pulse generation through optical rectification of femtosecond laser pulses in sugar crystals. The sugar crystals were grown...     

Optimizing Processing Conditions for Milk Coagulation Using the Hot Wire Method and Response Surface Methodology

ABSTRACT: :
To evaluate the relationship between the factors affecting coagulation, the hot wire method was used for direct measurements of the renneting milk process as well as a central composite design with 3 factors: rennet concentration (x₁), renneting pH (x₂), and temperature (x₃). Second-order models for maximum voltage (Y₁), time at maximum voltage (Y₂), and coagulation time (Y₃) were employed to generate response surface contours. Optimum conditions for cutting time were found with x₁= 0.0278 R.U./mL milk, x₂= 6.60, and x₃= 35 °C, for which the responses were Y₁= 2854 ± 171 μV, Y₂, = 14.08 ± 3.04 min, and Y₃= 7.16 ± 1.12 min. No significant differences (p > 0.01) were found between the 3 responses obtained in the experiment and the ones predicted by the models. The use of the objective and non-destructive monitoring of curd formation and the response surface methodology can be recommended to optimize milk coagulation.