High Strength, High Toughness Microalloyed Steel Forgings Produced with Relaxed Forging Conditions and No Heat Treatment

Three steel compositionswere designed and investigated as possible materials for the forging of a wheel hub geometry using the recrystallization controlled forging (RCF) process. Titanium nitride (TiN) technology was utilized to control prior austenite grain sizes (PAGS) and vanadium precipitation to strengthen ferrite. For processing, two cooperating systems were investigated, RCF, forrefinement of the PAGS, and controlled cooling, where interrupted direct quenching (IDQ) and indirect accelerated cooling (IAC) providedmultiple possible physical property combinations. The response of the steels to thermo-mechanical processing (TMP) was investigated to determine optimal forging conditions for refinement of the PAGS. The maximum reheat temperature to avoid grain coarsening, as well as the minimum forging temperature for complete recrystallization was determined.Ti and V additionswere found toelevate both temperatures. After, IDQ and IAC cooling paths were performed on the steels to yield desired microstructure products. Microstructures comprising predominantly polygonal ferrite,bainite and martensite were attainable in the laboratory samples. Finally, the steels were tested atMeadville Forging Company (MFC), a collaborator in this project. Here, each steel was subjected to the MFC standard forging routineand varying cooling paths were used. Mechanicaltesting samples were machined and tested from the forgings. The strengths increased with cooling rate and alloying, but the fully forged, hotwater quenchedbainiticsamplesdid not perform well, having lower strengthsthan the fast air cool to room temperature (ACRT) conditions. This is interpretedto be because of vthe low alloying, specifically the low carbon, limiting the strength of the bainite when present in large bainite phase percentages. The performance of the steels is compared with thoseof similar steelsand discussed from metallurgical standpoints. Methods of improving upon the current design of the steels are discussed. This research has demonstrated that low-carbon compositions, when subjected to proper RCFprocessing, are capable of being refined to equivalent circular prior austenite grain diameters approaching 10μm. Additionally, ultimate tensile strengths in the non-water quench to room temperature (WQRT)conditions were observed between 550MPa and 720MPa, and approaching 940MPa in the WQRT condition, with good toughness in all conditions

Coresets Meet EDCS: Algorithms for Matching and Vertex Cover on Massive Graphs

As massive graphs become more prevalent, there is a rapidly growing need for scalable algorithms that solve classical graph problems, such as maximum matching and minimum vertex cover, on large datasets. For massive inputs, several different computational models have been introduced, including the streaming model, the distributed communication model, and the massively parallel computation (MPC) model that is a common abstraction of MapReduce-style computation. In each model, algorithms are analyzed in terms of resources such as space used or rounds of communication needed, in addition to the more traditional approximation ratio. In this paper, we give a single unified approach that yields better approximation algorithms for matching and vertex cover in all these models. The highlights include: * The first one pass, significantly-better-than-2-approximation for matching in random arrival streams that uses subquadratic space, namely a $(1.5+\epsilon)$-approximation streaming algorithm that uses $O(n^{1.5})$ space for constant $\epsilon > 0$. * The first 2-round, better-than-2-approximation for matching in the MPC model that uses subquadratic space per machine, namely a $(1.5+\epsilon)$-approximation algorithm with $O(\sqrt{mn} + n)$ memory per machine for constant $\epsilon > 0$. By building on our unified approach, we further develop parallel algorithms in the MPC model that give a $(1 + \epsilon)$-approximation to matching and an $O(1)$-approximation to vertex cover in only $O(\log\log{n})$ MPC rounds and $O(n/poly\log{(n)})$ memory per machine. These results settle multiple open questions posed in the recent paper of Czumaj~et.al. [STOC 2018]

The Design and Effect of Power Electronics on Vibration-Based Energy Harvesting Methods.

Recent advancements in communication and low-power sensor nodes have led to innovative data acquisition systems for applications such as heart monitoring and forest-fire detection. Often these systems are in locations characterized by limited access to electrical power, yet they are in the presence of ambient mechanical vibrations. Therefore, energy harvesting from mechanical vibrations is proposed as a solution for powering these wireless sensor nodes. There are two devices that are commonly used for vibration-based energy harvesting: piezoelectric devices and electrostatic devices. This dissertation focuses on the power electronic interface between vibration energy harvesting devices and electrical energy storage elements. By including power electronic efficiency as a parameter in the analysis of variable-capacitance energy harvesting, new fundamental properties of these devices are derived: a threshold efficiency necessary for energy harvesting, analytical solutions for optimal harvesting conditions, a comparison of energy harvesting methods at practical power electronic efficiencies, and a comparison of energy harvesting capabilities of various device architectures. Case studies are presented to illustrate practical applications of the theory presented in this work. One case study demonstrates the advantage of using the Charge Pump Method for MEMs applications, and illustrates the use of these new fundamental properties to aid power electronic architecture selection. Ultimately, the analysis-aided design produces more than twice as much power as previous implementations on the same device. Recently, the dynamic active energy harvesting method has been proposed as a way to widen the bandwidth of resonant piezoelectric energy harvesters; however, the bandwidth extension is dependent on power electronic efficiency. In this dissertation a new energy harvesting system is proposed that includes a resonant inverter topology, in conjunction with new low-power analog control circuitry, in order to produce the first wideband autonomous dynamic active energy harvesting system. Experimental results using the Mide Volture V20w piezoelectric device shows that the harvested power is up to twice that of the adaptive rectifier method. These results include previously ignored loss mechanisms such as control losses, gating losses, and phase detection losses; making this system the first autonomous energy harvesting system of its kind.PhDElectrical Engineering: SystemsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120824/1/steinal_1.pd

Comparability of Functional MRI Response in Young and Old During Inhibition

When using fMRI to study age-related cognitive changes, it is important to establish the integrity of the hemodynamic response because, potentially, it can be affected by age and disease. However, there have been few attempts to document such integrity and no attempts using higher cognitive rather than perceptual or motor tasks. We used fMRI with 28 healthy young and older adults on an inhibitory control task. Although older and young adults differed in task performance and activation patterns, they had comparable hemodynamic responses. We conclude that activation during cognitive inhibition, which was predominantly increased in elders, was not due to vascular confounds or specific changes in hemodynamic coupling

Observation of the nonlinear Wood's anomaly on periodic arrays of nickel nanodimers

Linear and nonlinear magneto-photonic properties of periodic arrays of nickel nanodimers are governed by the interplay of the (local) optical response of individual nanoparticles and (non-local) diffraction phenomena, with a striking example of Wood's anomaly. Angular and magnetic-field dependencies of the second harmonic intensity evidence Wood's anomaly when new diffraction orders emerge. Near-infrared spectroscopic measurements performed at different optical wavelengths and grating constants discriminate between the linear and nonlinear excitation mechanisms of Wood's anomalies. In the nonlinear regime the Wood's anomaly is characterized by an order-of-magnitude larger effect in intensity redistribution between the diffracted beams, as compared to the linear case. The nonlinear Wood's anomaly manifests itself also in the nonlinear magnetic contrast highlighting the prospects of nonlinear magneto-photonics.Comment: 8 pages, 6 figure

Simultaneously Load Balancing for Every p-norm, With Reassignments

This paper investigates the task of load balancing where the objective function is to minimize the p-norm of loads, for pgeq 1, in both static and incremental settings. We consider two closely related load balancing problems. In the bipartite matching problem we are given a bipartite graph G=(Ccup S, E) and the goal is to assign each client cin C to a server sin S so that the p-norm of assignment loads on S is minimized. In the graph orientation problem the goal is to orient (direct) the edges of a given undirected graph while minimizing the p-norm of the out-degrees. The graph orientation problem is a special case of the bipartite matching problem, but less complex, which leads to simpler algorithms. For the graph orientation problem we show that the celebrated Chiba-Nishizeki peeling algorithm provides a simple linear time load balancing scheme whose output is an orientation that is 2-competitive, in a p-norm sense, for all pgeq 1. For the bipartite matching problem we first provide an offline algorithm that computes an optimal assignment. We then extend this solution to the online bipartite matching problem with reassignments, where vertices from C arrive in an online fashion together with their corresponding edges, and we are allowed to reassign an amortized O(1) vertices from C each time a new vertex arrives. In this online scenario we show how to maintain a single assignment that is 8-competitive, in a p-norm sense, for all pgeq 1

Using a cell phone-based glucose monitoring system for adolescent diabetes management

INTRODUCTION: Mobile technology may be useful in addressing several issues in adolescent diabetes management. PURPOSE: To assess the feasibility and acceptability of a cell phone glucose monitoring system for adolescents with type 1 diabetes and their parents. METHODS: The authors recruited patients with type 1 diabetes who had been diagnosed for at least 1 year. Each adolescent used the system for 6 months, filling out surveys every 3 months to measure their usability and satisfaction with the cell phone glucose monitoring system, as well as how use of the system might affect quality of family functioning and diabetes management. RESULTS: Adolescents reported positive feelings about the technology and the service, even though a concerning number of them had significant technical issues that affected continued use of the device. Nearly all thought that the clinic involvement in monitoring testing behavior was quite acceptable. The use of the Glucophone™ did not, however, significantly change the quality of life of the adolescents, their level of conflict with their parents, their reported self-management of diabetes, or their average glycemic control within the short time frame of the study. CONCLUSIONS: As a feasibility study of the technology, this work was successful in demonstrating that cell phone glucose monitoring technology can be used in an adolescent population to track and assist in self-monitoring behavior. The authors speculate that explicitly attempting to change behavior, perhaps with the use of behavioral contracts, would enhance the technology's ability to improve outcomes

Magnetic order and energy-scale hierarchy in artificial spin ice

In order to explain and predict the properties of many physical systems, it is essential to understand the interplay of different energy-scales. Here we present investigations of the magnetic order in thermalised artificial spin ice structures, with different activation energies of the interacting Ising-like elements. We image the thermally equilibrated magnetic states of the nano-structures using synchrotron-based magnetic microscopy. By comparing results obtained from structures with one or two different activation energies, we demonstrate a clear impact on the resulting magnetic order. The differences are obtained by the analysis of the magnetic spin structure factors, in which the role of the activation energies is manifested by distinct short-range order. This demonstrates that artificial spin systems can serve as model systems, allowing the definition of energy-scales by geometrical design and providing the backdrop for understanding their interplay.Comment: 8 pages, 5 figures (+ supplementary 6 pages, 4 figures

Probing Surface Defects of InP Quantum Dots Using Phosphorus Kα and Kβ X-ray Emission Spectroscopy

Synthetic efforts to prepare indium phosphide (InP) quantum dots (QDs) have historically generated emissive materials with lower than unity quantum yields. This property has been attributed to structural and electronic defects associated with the InP core as well as the chemistry of the shell materials used to overcoat and passivate the InP surface. Consequently, the uniformity of the core–shell interface plays a critical role. Using X-ray emission spectroscopy (XES) performed with a recently developed benchtop spectrometer, we studied the evolution of oxidized phosphorus species arising across a series of common, but chemically distinct, synthetic methods for InP QD particle growth and subsequent ZnE (E = S or Se) shell deposition. XES afforded us the ability to measure the speciation of phosphorus reliably, quantitatively, and more efficiently (with respect to both the quantity of material required and the speed of the measurement) than with traditional techniques, i.e., X-ray photoelectron spectroscopy and magic angle spinning solid state nuclear magnetic resonance spectroscopy. Our findings indicate that even with deliberate care to prevent phosphorus oxidation during InP core synthesis, typical shelling approaches unintentionally introduce oxidative defects at the core–shell interface, limiting the attainable photoluminescence quantum yields