Design and Fabrication of a Micro-Bearing Assembly to Study Rotor Friction

The objective of this investigation was to design and fabricate a metrology tool for measuring the wear in micro-bearings. The critical component of the tool was a silicon test bed consisting of a bearing shaft and a set of microchannels to direct an air stream onto the fins of a micro-rotor assembled onto the bearing shaft. By driving the micro-rotor pneumatically, surface interactions between the bearing and the rotor can be studied over time. The silicon test bed mates to a custom aluminum chuck which has provisions for sealing the test bed and supplying air pressure from an external source. The silicon test bed was successfully fabricated by bulk micromachining using Deep Reactive Ion Etching (DRIE). Test rotors were also fabricated using DRIE and manually placed onto the bearing shaft of the test bed. A glass cover slide, held in place by the aluminum chuck, was used to seal the top of the test bed. Test rotors were successfully rotated using a minimum input air pressure of 0.5 psi

Analytical and numerical modeling, fabrication and RF measurement techniques for RF planar micro-inductors on silicon

In mixed signal integrated circuits, the role of passives has become increasingly important. In particular, the characterization and implementation of an embedded planar coil inductor presents several challenges. The present work is a comprehensive study of micro inductors that includes analytical modeling, numerical simulation, in-house fabrication processes, circuit implementation in silicon, and RF measurement techniques. Although the inductor is widely integrated on silicon, there is still a need for closed form expressions for inductance and the quality factor. In addition, amongst the numerous commercially available simulation packages, there still is a need to identify the tool that best suits the design and implementation of micro-inductors on silicon. In this work, an analytical model is presented based on a desegmentation technique, which removes segments from a rectangular cavity to create the inductor coil geometry. Defining the Green\u27s function for each segment, the boundary conditions are applied to obtain a closed form expression for the Z matrix from which the inductance and Q have been obtained. For a numerical modeling, Ansoft\u27s High Frequency Structure Simulator (HFSS) is chosen as the preferred tool for an accurate and frequency dependent analysis. Several inductor geometrics have been modeled analytically and have been validated with HFSS where in each case there is excellent agreement. The model has also been successfully applied to irregularly shaped power planes that commonly occur in mixed signal circuits. The present work has established a fabrication process for micro-inductors using technologies available in the Semiconductor and Microsystems Fabrication Laboratory (SMFL) at RIT. A fabrication process has been developed to integrate inductors, transformers, capacitors, and PMOS (P-type Metal Oxide Semiconductor) transistors. Inductors and transformers have been made from copper and imbedded in a thick PECVD SiO₂ film. The process allows for an optional aluminum ground plane under the copper structures. Capacitors have been formed using the gate oxide as a dielectric and heavily doped silicon and aluminum as the electrodes. PMOS transistors have been implemented to control two varieties of LC tank circuits (parallel and series). The final contribution of the present work is establishing RF test methods for measuring inductance, and calculating the quality factor (Q). Experimental RF testing is performed using high frequency Cascade Microtech ground-signal-ground (GSG) probes and the 9100 probe station. Data has been captured using an Agilent 8363B network analyzer with a frequency range from 10 MHz to 40 GHz. A calibration procedure has been developed for a full two port measurement and a methodology has been optimized for measuring the impedance [Z] matrix and the scattering [S] matrix. The imput impedance is extracted from the [Z] matrix and Q has been calculated. There is excellent agreement between experimental results, numerical results from HFSS, and analytical results from the desegmentation technique

Fundamental Limitations of Cavity-assisted Atom Interferometry

Atom interferometers employing optical cavities to enhance the beam splitter pulses promise significant advances in science and technology, notably for future gravitational wave detectors. Long cavities, on the scale of hundreds of meters, have been proposed in experiments aiming to observe gravitational waves with frequencies below 1 Hz, where laser interferometers, such as LIGO, have poor sensitivity. Alternatively, short cavities have also been proposed for enhancing the sensitivity of more portable atom interferometers. We explore the fundamental limitations of two-mirror cavities for atomic beam splitting, and establish upper bounds on the temperature of the atomic ensemble as a function of cavity length and three design parameters: the cavity g-factor, the bandwidth, and the optical suppression factor of the first and second order spatial modes. A lower bound to the cavity bandwidth is found which avoids elongation of the interaction time and maximizes power enhancement. An upper limit to cavity length is found for symmetric two-mirror cavities, restricting the practicality of long baseline detectors. For shorter cavities, an upper limit on the beam size was derived from the geometrical stability of the cavity. These findings aim to aid the design of current and future cavity-assisted atom interferometers.Comment: 11 pages, 12 figure

Which rhizobia nodulate which legumes in New Zealand soils?

Recent work which genotypically characterised rhizobia of native, crop and weed legumes in New Zealand and examined their cross-nodulation ability is reviewed and related to earlier work with focus on New Zealand pasture systems. The New Zealand native legumes were exclusively effectively nodulated by novel strains of Mesorhizobium which did not nodulate crop or weed legumes. Clovers, lucerne, Lotus and grain legumes were effectively nodulated by different genera, species and biovars of rhizobia primarily originating from inoculum. Rhizobial symbionts of white clover have established over wide areas in New Zealand. Weed legumes are effectively nodulated by different genera/species of rhizobia depending on species. Bradyrhizobia that cross-nodulate lupins, gorse, European broom and tagasaste are widespread in New Zealand

Swift UVOT Observations of Core-Collapse SNe

We review recent UV observations of core-collapse supernovae (SNe) with the Swift Ultra-violet/Optical Telescope (UVOT) during its first two years. Rest-frame UV photometry is useful for differentiating SN types by exploiting the UV-optical spectral shape and more subtle UV features. This is useful for the real-time classification of local and high-redshift SNe using only photometry. Two remarkable SNe Ib/c were observed with UVOT -- SN2006jc was a UV bright SN Ib. Swift observations of GRB060218/SN2006aj began shortly after the explosion and show a UV-bright peak followed by a UV-faint SN bump. UV observations are also useful for constraining the temperature and ionization structure of SNe IIP. Rest-frame UV observations of all types are important for understanding the extinction, temperature, and bolometric luminosity of SNe and to interpret the observations of high redshift SNe observed at optical wavelengths.Comment: Figures are enlarged and colorized from print versio

Promoting Prosocial Responsiveness across Racial Divides through Mindfulness

In interracial and other intergroup interactions, prosocial emotions and actions are often undermined (Cikara & van Bavel, 2014). Perceiving psychological separateness between “us” and “them” – which is often an automatic, unintentional process – is psychological kindling for lower prosocial responsiveness that leads to prejudice, discrimination, aggressive conflict (Cikara, 2015). Recent research has shown that mindfulness, an open and unconditional attention to one’s present experiences, is associated with decreased automaticity and racial bias (Kang, Gruber, & Gray, 2013; Lueke & Gibson, 2014), barriers that hinder prosocial responsiveness (Trautwien, Schmidt, & Naranjo, 2014). Two experiments investigated whether brief mindfulness training promoted prosocial responsiveness toward an ostracized person of another race. Before witnessing a person of another race being excluded in an online ball-tossing game (Cyberball), participants in both studies were randomized to either an audio-recorded mindfulness training (MT), a structurally-equivalent attention control training (CT), or a no instruction control (NT). MI participants in Study 1 (N=124) showed trends towards higher empathic concern (p=.065), while MI participants in Study 2 (N=131) reported higher empathic concern for the excluded player (p\u3c0.05). MI participants in both studies wrote more comforting emails to them (p\u3c0.01), as coded for prosociality (c.f., Masten et al., 2011). Only in Study 2 did MI participants passed the ball more to the victim in an ‘all play’ game (p\u3c.05), presumably because their identity was less “known” than in Study 1; specifically, players’ photo images were loaded into the game in Study 1, but only first names were shared in Study 2. These studies underscore the potential for mindfulness training to foster sensitive attitudes across social and cultural lines within increasingly growing anonymous (i.e., online) contexts.https://scholarscompass.vcu.edu/uresposters/1222/thumbnail.jp