In-situ comprehensive calibration of a tri-port nano-electro-mechanical device.

We report on experiments performed in vacuum and at cryogenic temperatures on a tri-port nano-electro-mechanical (NEMS) device. One port is a very nonlinear capacitive actuation, while the two others implement the magnetomotive scheme with a linear input force port and a (quasi-linear) output velocity port. We present an experimental method enabling a full characterization of the nanomechanical device harmonic response: the nonlinear capacitance function C(x) is derived, and the normal parameters k and m (spring constant and mass) of the mode under study are measured through a careful definition of the motion (in meters) and of the applied forces (in Newtons). These results are obtained with a series of purely electric measurements performed without disconnecting/reconnecting the device, and rely only on known dc properties of the circuit, making use of a thermometric property of the oscillator itself: we use the Young modulus of the coating metal as a thermometer, and the resistivity for Joule heating. The setup requires only three connecting lines without any particular matching, enabling the preservation of a high impedance NEMS environment even at MHz frequencies. The experimental data are fit to a detailed electrical and thermal model of the NEMS device, demonstrating a complete understanding of its dynamics. These methods are quite general and can be adapted (as a whole, or in parts) to a large variety of electromechanical devices.

Visibility of dichalcogenide nanolayers.

Dichalcogenides with the common formula MX(2) are layered materials with electrical properties that range from semiconducting to superconducting. Here, we describe optimal imaging conditions for the optical detection of ultrathin, two-dimensional dichalcogenide nanocrystals containing single, double and triple layers of MoS(2), WSe(2) and NbSe(2). A simple optical model is used to calculate the contrast for nanolayers deposited on wafers with varying thicknesses of SiO(2). The model is extended for imaging using the green channel of a video camera. Using AFM and optical imaging we confirm that single layers of MoS(2) and WSe(2) can be detected on 90 and 270 nm SiO(2) using optical means. By measuring contrast under broadband green illumination we are also able to distinguish between nanostructures containing single, double and triple layers of MoS(2) and WSe(2.) We observe and discuss discrepancies in the case of NbSe(2).

Mesoscopic size effects on the thermal conductance of silicon nanowire.

We report the measurement of thermal conductance of silicon nanowires at low temperature. It is demonstrated that the roughness at the nanometer scale plays a crucial role for the phonon transport in low-dimensional samples. To this end, using e-beam lithography, nanowires of size 200 nm by 100 nm and 10 microm long have been nanofabricated. Their thermal properties have been measured using the 3 omega method between 0.3 and 6 K. The change in the temperature behavior of the thermal conductance (quadratic temperature dependence of K(T)) is a signature of an intermediate regime lying between the classical Casimir regime and the quantum regime. The Casimir-Ziman model is used to show that this specific behavior originates in mesoscopic samples where the dominant phonon wavelength becomes commensurate to the characteristic length of the roughness of the nanowire surfaces.

Effect of context salience on heart rate orienting and habituation in preweanling and periadolescent rats.

Previous research indicates that target learning is facilitated in the presence of strong extraneous sensory cues (e.g., salient contextual cues) in infant, but not adult, rats (McKinzie & Spear, 1995). The present study assessed whether such facilitation of conditioning is due to age-related differences in the effect of a salient context on processing of the conditioned stimulus (tone in this case). Preweanling and periadolescent rats were presented with a tone in either the presence (salient context) or absence (plain context) of a potent odorant. Magnitude of the heart rate orienting response to the target stimulus and its subsequent rate of habituation served as dependent variables. The results revealed that preweanling, but not periadolescent, rats showed greater cardiac orienting to the auditory stimulus in the salient than in the plain context. The results suggest that a salient context may influence stimulus processing by increasing the perceived salience and, perhaps in terms of perceived intensity, of the target stimulus.

Anaesthesia for posterior cervical osteotomy.

We have studied 22 consecutive cases of posterior cervical osteotomy done at the Toronto East General Hospital between October 1967 and November 1973. The anaesthetic management is discussed in some detail and consists of psychological preparation of the patient, and neuroleptanalgesia with infiltration with local anaesthetic by the surgeon. The reasons for this choice of technique have been discussed in some detail. There were no deaths during operation, but one patient suffered collapse on the table, which was thought to be due to air embolism. One patient died three weeks post-operatively of pulmonary embolism. Experience in anaesthetizing patients who require operation after previous posterior cervical osteotomy is mentioned briefly and techniques are recommended for successful management of such cases.