ABSTRACT
Dynamic measurement of femtometer-displacement vibrations in mechanical resonators at microwave frequencies is critical for a number of emerging high-impact technologies including 5G wireless communications and quantum state generation, storage, and transfer. However, the resolution of continuous-wave laser interferometry, the method most commonly used for imaging vibration wavefields, has been limited to vibration amplitudes just below a picometer at several gigahertz. This is insufficient for these technologies since vibration amplitudes precipitously decrease for increasing frequency. Here we present a stroboscopic optical sampling approach for the transduction of coherent super high frequency vibrations. Phase-sensitive absolute displacement detection with a noise floor of 55 fm/âHz for frequencies up to 12 GHz is demonstrated, achieving higher bandwidth and significantly lower noise floor simultaneously compared to previous work. An acoustic microresonator with resonances above 10 GHz and displacements smaller than 70 fm is measured using the presented method to reveal complex mode superposition, dispersion, and anisotropic propagation.
ABSTRACT
We examined the effects of chronic nicotine exposure and dietary salt on the arterial blood pressure (BP) changes learned in response to an acute behavioral stress in the Dahl salt-sensitive rat. Four groups were tested: low salt + vehicle; low salt + nicotine; high salt + vehicle; and high salt + nicotine. Rats were fed a low-salt (0.08% NaCl) or a high-salt (8% NaCl) diet for 4 wk; 2.4 mg. kg(-1). day(-1) nicotine or vehicle was given via an implanted osmotic minipump for the last 2 wk. All rats were conditioned by following one tone (CS+) with a 0.5-s tail shock; another tone (CS-) was never followed by shock. CS+ in low salt + vehicle and high salt + vehicle-treated rats evoked an initial arterial BP increase (C(1)), a component of the startle response, and an ensuing, smaller, but more sustained, pressor response (C(2)), which is acquired with training. In these rats, both C(1) and C(2) evoked by CS- were significantly smaller than those to CS+, demonstrating that these groups discriminated between the two tests. Conversely, although the low salt + nicotine-treated rats had both the C(1) and C(2) components of the conditional arterial pressure response, they did not discriminate between CS+ and CS-. Finally, the high salt + nicotine group failed to both discriminate between tones and acquire (i.e., learn) the C(2) response. The unconditional response to shock did not differ between groups. We conclude that combined exposure to high salt and to nicotine inhibits the salt-sensitive animal's acquisition of a learned conditional BP response, perhaps because nicotine acts preferentially on those central processes required for associative learning versus those involved in orientating to external stimuli.