Graphene Spin Transistor

Graphitic nanostructures, e.g. carbon nanotubes (CNT) and graphene, have been proposed as ideal materials for spin conduction[1-7]; they have long electronic mean free paths[8] and small spin-orbit coupling[9], hence are expected to have very long spin-scattering times. In addition, spin injection and detection in graphene opens new opportunities to study exotic electronic states such as the quantum Hall[10,11] and quantum spin Hall[9] states, and spin-polarized edge states[12] in graphene ribbons. Here we perform the first non-local four-probe experiments[13] on graphene contacted by ferromagnetic Permalloy electrodes. We observe sharp switching and often sign-reversal of the non-local resistance at the coercive field of the electrodes, indicating definitively the presence of a spin current between injector and detector. The non-local resistance changes magnitude and sign quasi-periodically with back-gate voltage, and Fabry-Perot-like oscillations[6,14,15] are observed, consistent with quantum-coherent transport. The non-local resistance signal can be observed up to at least T = 300 K

Correction of Saccade-Induced Midline Errors in Responses to Pure Disparity Vergence Stimuli.

Purely symmetrical vergence stimuli aligned along the midline (cyclopean axis) require only a pure vergence response. Yet, in most responses saccades are observed and these saccades must either produce an error in the desired midline response or correct an error produced by asymmetry in the vergence response. A previous study (Semmlow, et al. 2008) has shown that the first saccade to appear in a response to a pure vergence stimulus usually increased the deviation from the midline, although all subjects (N = 12) had some responses where the initial saccade corrected a vergence induced midline error. This study focuses on those responses where the initial saccade produces an increased midline deviation and the resultant compensation that ultimately brings the eyes to the correct binocular position. This correction is accomplished by a higher level compensatory mechanism that uses offsetting asymmetrical vergence and/or corrective saccades. While responses consist of a mixture of the two compensatory mechanisms, the dominant mechanism is subject-dependent. Since fixation errors are quite small (minutes of arc), some feedback controlled physiological process involving smooth eye movements, and possibly saccades, must move the eyes to reduce binocular error to fixation disparity levels

QF-MAC: Adaptive, Local Channel Hopping for Interference Avoidance in Wireless Meshes

The throughput efficiency of a wireless mesh network with potentially malicious external or internal interference can be significantly improved by equipping routers with multi-radio access over multiple channels. For reliably mitigating the effect of interference, frequency diversity (e.g., channel hopping) and time diversity (e.g., carrier sense multiple access) are conventionally leveraged to schedule communication channels. However, multi-radio scheduling over a limited set of channels to minimize the effect of interference and maximize network performance in the presence of concurrent network flows remains a challenging problem. The state-of-the-practice in channel scheduling of multi-radios reveals not only gaps in achieving network capacity but also significant communication overhead. This paper proposes an adaptive channel hopping algorithm for multi-radio communication, QuickFire MAC (QF-MAC), that assigns per-node, per-flow ``local'' channel hopping sequences, using only one-hop neighborhood coordination. QF-MAC achieves a substantial enhancement of throughput and latency with low control overhead. QF-MAC also achieves robustness against network dynamics, i.e., mobility and external interference, and selective jamming attacker where a global channel hopping sequence (e.g., TSCH) fails to sustain the communication performance. Our simulation results quantify the performance gains of QF-MAC in terms of goodput, latency, reliability, communication overhead, and jamming tolerance, both in the presence and absence of mobility, across diverse configurations of network densities, sizes, and concurrent flows

The effect of mechanism design on the performance of a quadruped walking machine

The objective of this paper is to investigate the effect of mechanism design on the performance of a quadruped walking machine. For studying the effect of mechanism design on the performance of a quadruped walking machine, four designs with different crank and leg arrangements are proposed and analyzed. The performance of the walking machine, including the stance leg sequence, foot trajectory, pitch angle, and dynamic response of the quadruped walking machine are investigated and compared with the existing design. The results show that the phrase angle between front and rear legs on the same side should be 0° or 90° and the one between the legs on the different sides should be 180°. And, the design with the front and rear legs bent in the same direction has better performance in dynamic responses. The results of this study can serve as a reference for future design and optimization of quadruped walking machines

semiconducting carbon nanotube transistors: electron and spin transport properties

Single-walled carbon nanotubes (SWNTs) have attracted great interest both scientifically and technologically due to their long mean free paths and high carrier velocities at room temperature, and possibly very long spin-scattering lengths. This thesis will describe experiments to probe the charge-and spin-transport properties of long, clean individual SWNTs prepared by chemical vapor deposition and contacted by metal electrodes. A SWNT field-effect transistor (SWNT-FET) has been shown to be sensitive to single electrons in charge traps. A single charge trap near a SWNT-FET is explored here using both electronic and scanned-probe techniques, and a simple model is developed to determine the capacitances of the trap to the SWNT and gate electrode. SWNTs are contacted with ferromagnetic electrodes in order to explore the transport of spin-polarized current through the SWNT. In some cases spin-dependent transport was observed, verifying long spin scattering lengths in SWNT. However, in many cases no spin-dependent effects were observed; these results will be discussed in the context of the present state of results in the literature. Semiconducting SWNTs (s-SWNTs) with Schottky-barrier contacts are measured at high bias. Nearly symmetric ambipolar transport is observed, with electron and hole currents significantly exceeding 25 µA, the reported current limit in m-SWNTs. Four simple models for the field-dependent velocity (ballistic, current saturation, velocity saturation, and constant mobility) are studied in the unipolar regime; the high-bias behavior is best explained by a velocity saturation model with a saturation velocity of 2 x 10^7 cm/s. A simple Boltzmann equation model for charge transport in s-SWNTs is developed with two adjustable parameters, the elastic and inelastic scattering lengths. The model predicts velocity saturation rather than current saturation in s-SWNTs, in agreement with experiment. Contact effects in s-SWNT-FET are explored by electrically heating the devices. These experiments resolve the origin of nanotube p-type behavior in air by showing that the observed p-type behavior upon air exposure cannot be explained by change in contact work function, but is instead due to doping of the nanotube. Modest doping of the SWNT narrows the Schottky Barriers and provides a high-conductance Ohmic tunnel contact from electrode to SWNT