The Effects of Altimeter Instrument Noise on the Estimation of the Wavenumber Spectrum of Sea Surface Height

The wavenumber spectrum of sea surface height (SSH) observed by satellite altimetry was analyzed by Xu and Fu. The spectral shape in the wavelength range of 70–250 km was approximated by a power law, representing a regime governed by geostrophic turbulence theories. The effects of altimeter instrument noise were assumed insignificant at wavelengths longer than 70 km. The authors reexamined the assumption in the study. Using nearly simultaneous observations made by Jason-1 and Jason-2 during their cross-calibration phase, this study found that the white noise level of altimetry measurement was best estimated from the spectral values at wavelengths from 25 to 35 km. After removing a white noise level based on such estimate from the SSH spectrum, the spectral slope values changed significantly over most of the oceans. A key finding is that the spectral slopes are generally steeper than k−2 (k is wavenumber) poleward of the 20° latitudes, where flatter spectral slopes in some regions have previously caused problems for dynamic interpretations. The new results indicate that the spectral slopes in the core regions of the major ocean current systems have values between the original geostrophic turbulence theory and the surface quasigeostrophic theory. The near k−4 spectrum suggests that the sea surface height variability at these wavelengths in the high eddy energy regions might be governed by frontogenesis.

Interactions in Perceived Quality of Auditory-Visual Displays

The quality of realism in virtual environments (VEs) is typically considered to be a function of visual and audio fidelity mutually exclusive of each other. However, the VE participant, being human, is multimodal by nature. Therefore, in order to validate more accurately the levels of auditory and visual fidelity that are required in a virtual environment, a better understanding is needed of the intersensory or crossmodal effects between the auditory and visual sense modalities. To identify whether any pertinent auditory-visual cross-modal perception phenomena exist, 108 subjects participated in three experiments which were completely automated using HTML, Java, and JavaScript programming languages. Visual and auditory display quality perceptions were measured intraand intermodally by manipulating the pixel resolution of the visual display and Gaussian white noise level, and by manipulating the sampling frequency of the auditory display and Gaussian white noise level. Statistically significant results indicate that high-quality auditory displays coupled with highquality visual displays increase the quality perception of the visual displays relative to the evaluation of the visual display alone, and that low-quality auditory displays coupled with high-quality visual displays decrease the quality perception of the auditory displays relative to the evaluation of the auditory display alone. These findings strongly suggest that the quality of realism in VEs must be a function of both auditory and visual display fidelities inclusive of each other.

A model of defect-induced pairing in mixing layers

Experiment have shown that the well-known vortex pairing process may take place first in defect regions where the fundamental structure is weakest. A model is introduced here to describe this defect-induced pairing process. The model is constructed in such a way that, in a certain parameter range, a stable fundamental mode and a stable subharmonic mode may coexist. The numerical simulation demonstrates that, when initial conditions consist of a dominant fundamental with one or more defects, the subharmonic component is preferentially generated in the cores of these defects. Moreover, the results also indicate that pairing may first commence wherever the fundamental mode is weakest provided the white-noise level of the subharmonic is high enough. The numerical results are in good agreement with experimental observations.

INVESTIGATION OF rf SQUID BEHAVIOR AT LIQUID NITROGEN TEMPERATURES

An investigation of the performance of two hole Y–Ba–Cu–O rf-SQUID operating at liquid nitrogen temperatures are reported. The magnetic flux white noise level ~ 10−4Φ0 (Φ0 = 2.07 × 10−15 Wb ) is determined by amplifier noise since it is equal to the white noise level of a low-temperature SQUID with the same amplifier. Overall 1/f fluctuations develop at frequencies below 20 Hz. The measurement methods and the values of the main parameters are given.

Stereotyped Behaviors of Chimpanzees: Relation to General Arousal and Alternative Activities

Chimpanzees raised without their mothers develop abnormal stereotyped behaviors not found in mother-raised animals. Two studies tested the hypotheses that moment-to-moment fluctuations of stereotyped behaviors are related to the level of general arousal and to the extent to which alternative activities are performed. The first study showed that body rocking or swaying is positively related to white noise level and to food deprivation. In the second experiment, rocking and swaying decreased during habituation to a novel situation and returned to a high level following administration of amphetamine. Activities alternative to stereotyped movements were evoked in a third experiment and produced a decrement in rocking and swaying. In general, the evidence suggests a positive relationship between arousal and rocking and swaying; the relationship of arousal to other stereotyped acts was not as regular. No behavior in the repertoire of mother-raised animals was found to be homologous to Rock-Sway. The relationship between the various behavior categories studied was related to S's rearing history, momentary arousal level, and the extent to which the cues in the situation evoked the various behaviors.