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Recently, human and user-centered design methods have challenged older system-centered practices, enriching resources and providing better technological artifacts for end-users. This article argues that though design has become more user-centered, something is still lacking: more opportunities exist for articulating feedback already present in technology-culture networks. To encourage the recovery of this feedback, this article examines discourses surrounding transportation technology and the Chora, the variety of stakeholders who shape the progression of technology through use, negation, or re-appropriation. While this article is far from a programmatic or procedural document, it suggests opening design processes to a variety of cultural inputs beyond those marked as 'users.' It attempts to open a space for technical communicators in these multifaceted feedback loops, where Choral influences are articulated and rearticulated for more effective transportation design. doi: 10.2190/TW.40.3.b

We present experimental and theoretical results obtained from the study of the effects of optical feedback in low-cost Fabry-Perot laser diodes due to the presence of an external cavity created by an external reflective or diffusive vibrating target. Experimental results show that a change in the length of the external cavity produces the well-known amplitude modulation of the optical output power and, depending on the amount of optical feedback, a subperiodicity appears in the amplitude modulation of the output power. The experiments show that the subperiodicity appears independently of the length of the external cavity and is due to mode hopping between different longitudinal laser modes. Numerical analysis focused on the effects observed support that the mode hop occurs between modes whose round-trip phase delay along the external cavity is out of phase, thus producing a subperiodicity of the total amplitude modulation. OCIS codes: 140.5960, 120.3180, 120.7280, 280.3420.

The disturbance observer (DOB) is known to be effective in enhancing the performance of dynamic systems in the presence of disturbances. In general, the disturbance rejection performance and robustness of DOBs depend on the order of the Q-filter, which is a low pass filter, and its time constant. In this paper, a new multi-loop DOB, improving the performance of DOB, is presented and its robust stability is proven using linear fractional transformation. It is possible to improve the sensitivity function with additional external-loop DOBs which do not significantly affect the complementary sensitivity function. The proposed new multi-loop DOB is applied to a commercial optical disk drive tracking servo system. Experimental results show that the proposed multi-loop DOB is an effective method in rejecting disturbance as well as improving the tracking performance. Index Terms--Disturbance observer (DOB), multi-loop DOB, optical disk drive, tracking control.

We report the experimental results to continuously tune the coherence length of a semiconductor laser using an optical feedback scheme. The coherence length can be controlled by adjusting the feedback strength when a semiconductor laser operates in a coherence collapse regime. Fine structures of the fringe visibility of the laser output show that the coherence length of the semiconductor laser can be shortened from several meters of the solitary laser to 100 [micro]m by the long-cavity optical feedback technique. Experimental results indicate that the coherence length of the laser, depending strongly on the feedback strength, is insensitive to its bias current. OCIS codes: 030.1640, 140.1540, 140.2020, 190.3100.

A new L-band automatic-gain-controlled (AGC) erbium-doped fiber amplifier (EDFA) for dense wavelength-division-multiplexing transmission systems is presented, in which a single 1480 nm laser with an internal thermoelectric cooler is used as a primary pump for stable amplification. All C-band amplified spontaneous emission (ASE) is recycled by the secondary pump to enhance the gain efficiency. A fraction of the output signal is used as an electrical feedback monitor for the AGC to improve the gain-clamped (GC) flatness. Experimental results prove that the AGC EDFA has a gain flatness of better than 0.46 dB/40 nm, i.e., below 1.5%, and a higher gain of approximately 36.5 dB compared to that of approximately 35.3 dB for the conventional GC EDFA at -30 dBm input signal power. The best gain flatness of [+ or -] 0.25 dB can be achieved over the dynamic range greater than 20 dB. The dynamic range of noise figure is between 6.7 and 7.1. The 3 dB down bandwidth is more than 40nm. Overall dynamics measurements for the AGC EDFA feedback stabilization have been carried out. The recorded corresponding rise time of 1.565 ms indicates that the system does not exhibit any overshoot of gain or ASE variation due to the signal at the beginning of the pulse. OCIS codes: 140.3280, 230.4480, 060.4510.

We investigated the influence of amplitude modulation (AM) noise and phase modulation (PM) noise of a laser source on the frequency stability in frequency stabilization systems. We estimated the frequency stability and evaluated the efficacy of a noise reduction technique (the Doppler-trend subtraction method) of a laser diode frequency stabilization system, where enhanced intensity noise arising from PM-to-AM noise conversion through a reference gas cell is reduced using the technique employed in modulation transfer spectroscopy. To evaluate the relationship between the laser's intrinsic noise and its frequency stability, we performed noise spectrum measurements and formulated frequency stability in addition to measuring Allan standard deviation. As a result, it is found that the extra noise generated in PM-to-AM conversion is efficiently removed by the Doppler-trend subtraction method and that within the feedback bandwidth, the frequency stability becomes 1 order of magnitude better than that without the method. OCIS codes: 140.3425, 300.6260, 300.6460, 300.6320.

We propose a new optical architecture for the laser optical feedback imaging (LOFI) technique which makes it possible to avoid the adverse effect of the optical parasitic backscattering introduced by all the optical interfaces located between the laser source and the studied object. This proposed setup needs no specific or complex alignment, which is why we can consider the proposed setup to be self-aligned. We describe the principle used to avoid the parasitic backscattering contributions that dramatically deteriorate amplitude and phase information contained in the LOFI images. Finally, we give a successful demonstration of amplitude and phase images obtained with this self-aligned setup in the presence of a parasitic reflection. OCIS codes: 110.3175, 110.2970, 110.3080, 110.4280, 280.3420.

We present a heterodyne Michelson interferometer for vibration measurement in which feedback is used to obviate the need to unwrap phase data. The Doppler shift of a vibrating target mirror is sensed interferometrically and compensated by means of a voltage-controlled oscillator driving an acousto-optic modulator. For frequencies within the servo bandwidth, the oscillator control voltage provides a direct measurement of the target velocity. Outside the servo bandwidth, phase-sensitive detection is used to evaluate high-frequency displacements. This approach is of great interest for the frequently-occurring situation where vibration amplitudes at low frequency exceed an optical wavelength, but knowledge of the vibration spectrum at high frequency is important as well. OCIS codes: 120.3180, 120.7250, 120.3930.

ABSTRACT. The control of a cursor on a computer monitor offers a simple means of exploring the limits of the plasticity of human visuomotor coordination. The authors explored the boundary [...]

Sensory abnormalities and weak central coherence (WCC), a processing bias for features and local information, are important characteristics associated with autism. This paper introduces a self-organizing map (SOM)-based computational model of sensory abnormalities in autism, and of a feedback system to compensate for them. Feedback relies on a measure of balance of coverage over four (sensory) domains. Different methods to compute this measure are discussed, as is the flexibility to configure the system using different control mechanisms. Statistically significant improvements throughout training are demonstrated for compensation of a simple (i.e., monotonically decreasing) hypersensitivity in one of the domains. Fine-tuning control parameters can lead to further gains, but a standard setup results in good performance. Significant improvements are also shown for complex hypersensitivities (i.e., increasing and decreasing through time) in two domains. Although naturally best suited to compensate hypersensitivities--stimuli filtering may mitigate neuron migration to a hypersensitive domain--the system is also shown to perform effectively when compensating hyposensitivities. With poor coverage balance in the model akin to poor global perception, WCC would be consistent with inadequate feedback, resulting in uncontrolled hyper- and/or hyposensitivities characteristic of autism, as seen in the topologies of the resulting SOMs. Index Terms--Autism, self-organizing maps (SOMs), sensory abnormalities, weak central coherence (WCC).

Purpose: Northern Digital Instruments (NDI; Waterloo, Ontario, Canada)manufactures a commercially available magnetometer device called Aurora that features real-time display of sensor position tracked in 3 dimensions. To test its potential [...]

We consider a stabilization problem of approximately feedback linearizable systems. We introduce a perturbation parameter by applying high-gain feedback and use both the feedback linearization method and the singular perturbation method for the controller design. Through this, we can overcome the rigorous conditions of the feedback linearization method and can reduce the dimension of the slow model of the singularly perturbed system. Index Terms--Feedback linearization, Lyapunov method, nonlinear system, singular perturbation method.

Abstract * We examined scalp-recorded event-related potentials following feedback stimuli in a time-estimation task. Six hundred msec after indicating the end of a l see interval, subjects received a visual, [...]

1. INTRODUCTION Researchers have proposed a diverse range of haptic interfaces for more realistic communication methods with computers. Force feedback devices, which have attracted the most attention with their capacity [...], This paper presents a haptic stylus interface with a built-in compact tactile display module and an impact module as well as empirical studies on Braille, button, and texture display. We describe preliminary evaluations verifying the tactile display's performance indicating that it can satisfactorily represent Braille numbers for both the normal and the blind. In order to prove haptic feedback capability of the stylus, an experiment providing impact feedback mimicking the click of a button has been conducted. Since the developed device is small enough to be attached to a force feedback device, its applicability to combined force and tactile feedback display in a pen-held haptic device is also investigated. The handle of pen-held haptic interface was replaced by the pen-like interface to add tactile feedback capability to the device. Since the system provides combination of force, tactile and impact feedback, three haptic representation methods for texture display have been compared on surface with 3 texture groups which differ in direction, groove width, and shape. In addition, we evaluate its capacity to support touch screen operations by providing tactile sensations when a user rubs against an image displayed on a monitor.