New thermocouple-based microwave/millimeter-wave power sensor MMIC techniques in GaAs

We describe a new RF and microwave power sensor monolithic microwave integrated circuit design. The circuit incorporates a number of advances over existing designs. These include a III–V epitaxial structure optimized for sensitivity, the figure-of-merit applicable to the optimization, a mechanism for in-built detection of load ageing and damage to extend calibration intervals, and a novel symmetrical structure to linearize the high-power end of the scale

Modulating the Conducting Orbitals of Single Molecules Through Chemical Design

The last two decades have seen huge improvements in measuring the conductance of single molecules, especially with the establishment of the scanning tunneling microscope break-junction (STM-BJ) method. The availability of such a robust and reliable measurement technique allows for the study of more exotic molecules with built-in functionality. In this thesis, we employ creative chemical design to manipulate transport in a single molecule junction by tuning the conducting frontier orbitals. We investigate three classes of materials – thiophene dioxides, mixed-valence bis(triarylamines), and benzotriazinyl-based Blatter radicals. Within each system, we probe changes in conducting behavior or interfacial interactions that arise from modifying the molecular structure. First, we demonstrate that a family of thiophene pentamers, which typically conduct through their highest occupied molecular orbital (HOMO), can be induced to conduct through their lowest unoccupied molecular orbital (LUMO) instead. This is akin to switching between from hole to electron transport. The switching was achieved using chemical modifications that drastically lower the LUMO level toward the Fermi energy of gold: oxidation at the sulfur position to form thiophene dioxides combined with installing electron-withdrawing groups at the 3- and 4-positions of the thiophene moiety. The ability to tune HOMO versus LUMO transport is potentially useful for assembling molecular circuits with n- and p-type components. Next, we found that oxidation of bis(triarylamine) molecular wires into their mixed-valence state shifts their conducting orbitals close to the Fermi energy of gold, making these wires highly conducting. We measured the length dependent transport of three bis(triarylamine) molecules. In their neutral state, the conductance of these compounds decreases with increasing length, which is observed for many different systems. However, when they are chemically oxidized, the mixed-valence molecular wires show an increase in conductance with increasing length. Such wires that maintain good electrical transport over long distances are valuable for building efficient molecular devices. We then investigated the interaction of half-filled orbitals in organic radicals with gold substrates to explore the potential of these compounds for spintronic and magnetic applications. We found that a Blatter radical functionalized with gold-binding thiomethyl groups displays different charge transfer behavior depending on the environment. Under ultra-high vacuum, X-ray spectroscopy shows that the radical molecules in contact with the gold substrate gain a charge from gold and their singly unoccupied molecular orbitals get filled. Contrastingly, in solution-based single molecule measurements, the radical loses the electron from its singly occupied molecular orbital instead, and only the conductance of the oxidized species is detected. We further probed the nature of charge transfer between the Blatter radical and gold in ultra-high vacuum by comparing spectroscopic measurements from three different derivatives. The derivative that was functionalized with two thiomethyl groups in order for it to be measured in the STM-BJ was the only molecule to undergo charge transfer in ultra-high vacuum. Two other Blatter derivatives that had only one and no thiomethyl groups did not show the same charge transfer; these retained their radical character even when in contact with the gold substrate. Therefore, the results indicate that only one of the thiomethyl groups mediates charge transfer between radical and substrate. The body of work presented herein shows that chemical modifications to old and new systems can be used to modulate transport in junctions via the intrinsic character of the molecules rather than external engineering factors. Thiophene dioxides are a relatively nascent class of materials that already show versatility as molecular conductors, while organic mixed-valence and radical systems have been heavily researched in other fields but less so in molecular electronics. This thesis therefore seeks to encourage further research that takes advantage of the unique electronic structure of these materials systems to discover new transport phenomena

IVD Delivery System

Cepheid is a molecular diagnostics company that has assigned our senior project team to design a system that automates the current manual transportation of samples between two laboratory rooms. With the focus of retaining the sanitary integrity of both the samples as well as the initial cleanroom, also referred to as the packaging laboratory, our team has designed an extension of the current passthrough that will contain all other subsystems. In order to automate the transportation of the samples, the design employs a track and trolley system to be purchased and mounted within the passthrough. A verification prototype was built and tested to ensure the design would work as intended, modeling a five-foot section of the entire sixty-foot path. This prototype features an interlocking system to eliminate any potential for backflow between lab rooms. Samples are carried in a hanging bag that the team has designed to not spill any of the cartridge’s contents. Additionally, a virtual model was made and used to perform varying load tests to prove the validity of the materials selected for the passthrough. While effective, the proposed design could be improved in efficiency, though regardless of the decisions made by Cepheid regarding implementation, the designed passthrough extension and interlocking system could be used in any industry backflow prevention scenario

The Masses of Transition Circumstellar Disks: Observational Support for Photoevaporation Models

We report deep Sub-Millimeter Array observations of 26 pre-main-sequence (PMS) stars with evolved inner disks. These observations measure the mass of the outer disk (r ~20-100 AU) across every stage of the dissipation of the inner disk (r < 10 AU) as determined by the IR spectral energy distributions (SEDs). We find that only targets with high mid-IR excesses are detected and have disk masses in the 1-5 M_Jup range, while most of our objects remain undetected to sensitivity levels of M_DISK ~0.2-1.5 M_Jup. To put these results in a more general context, we collected publicly available data to construct the optical to millimeter wavelength SEDs of over 120 additional PMS stars. We find that the near-IR and mid-IR emission remain optically thick in objects whose disk masses span 2 orders of magnitude (~0.5-50 M_Jup). Taken together, these results imply that, in general, inner disks start to dissipate only after the outer disk has been significantly depleted of mass. This provides strong support for photoevaporation being one of the dominant processes driving disk evolution.Comment: Accepted for publication by ApJL, 4 pages and 3 figure

Separable Hamiltonian Neural Networks

The modelling of dynamical systems from discrete observations is a challenge faced by modern scientific and engineering data systems. Hamiltonian systems are one such fundamental and ubiquitous class of dynamical systems. Hamiltonian neural networks are state-of-the-art models that unsupervised-ly regress the Hamiltonian of a dynamical system from discrete observations of its vector field under the learning bias of Hamilton's equations. Yet Hamiltonian dynamics are often complicated, especially in higher dimensions where the state space of the Hamiltonian system is large relative to the number of samples. A recently discovered remedy to alleviate the complexity between state variables in the state space is to leverage the additive separability of the Hamiltonian system and embed that additive separability into the Hamiltonian neural network. Following the nomenclature of physics-informed machine learning, we propose three separable Hamiltonian neural networks. These models embed additive separability within Hamiltonian neural networks. The first model uses additive separability to quadratically scale the amount of data for training Hamiltonian neural networks. The second model embeds additive separability within the loss function of the Hamiltonian neural network. The third model embeds additive separability through the architecture of the Hamiltonian neural network using conjoined multilayer perceptions. We empirically compare the three models against state-of-the-art Hamiltonian neural networks, and demonstrate that the separable Hamiltonian neural networks, which alleviate complexity between the state variables, are more effective at regressing the Hamiltonian and its vector field.Comment: 11 page

Prior band-resisted squat jumps improved running time, rating of perceived exertion, and neuromuscular performance in middle-distance runners

There is a need for more research that examines the time course of neuromuscular alterations that occur during middle-long distance running. A growing body of evidence suggests that post-activation potentiation (PAP) is a prominent neuromuscular alteration that aids in the enhancement and maintenance of force production. PAP conditioning contractions integrated into warm-up protocols have been shown to enhance subsequent performance, yet the role PAP plays in endurance performance remains under-studied. The aim of this study was to characterize the time course of the effects of a PAP conditioning stimulus (band-resisted jump squat protocol) on a subsequent 5 X 1 km running trial. This study examined neuromuscular properties (ITT, MVC, EMG, drop jump) and metabolic properties (RPE, HR). It was hypothesized that performing a 5RM band-resisted jump squat protocol as part of a standardized running-specific warm-up in a group of endurance runners would induce significant measurable PAP effects during the course of a subsequent 5 X 1 km time trial run and up to 10 minutes post-run protocol. The neuromuscular and performance changes resulted in decreased time to complete the running task (3.6%) in the intervention session, increased force generation (9.5%) throughout both trials, increased voluntary activation (10%) in the intervention session, and a lack of impaired evoked contractile properties. These results serve as evidence of measurable neuromuscular changes occurring during and after the subsequent running trial. It is plausible that the band-resisted jump squat protocol served to increase performance and physiological measures and is attributable to post-activation potentiation, heighted central-pacing strategies, and increased stretch-shortening cycle efficiency

A Decision-support Model for Product End-of-life Planning

Ph.DDOCTOR OF PHILOSOPH