149 research outputs found
Sounds Local, 1997 October 25
No full textRe-airing of July 29, 1994 segment of the interview with Beau Biggs of K.M. Biggs Tractor in Lumberton and R.W. Wilkins, agri-business advisor to North Carolina Governor Jim Hunt, on the state of tobacco farms and market in Robeson County; Re-airing of July 29, 1994 segment of the interview with author Phillip Gerard on his novel, Desert Kill, a murder mystery set in Arizona; Gattaca (film) review by WHQR's film commentator, Steve Taylor; Overview of upcoming events on the cultural calendar
Transient experimentation and modeling of a multi-microchannel evaporator
No full text2020 Spring.Includes bibliographical references.Laser diodes are semiconductor devices that convert electrical energy into light. Often, diodes are arrayed closely together to produce high optical output. Commercially available diode arrays show electro-optical efficiencies of ~50%, resulting in high heat fluxes from these compact devices. Active thermal management is warranted to prevent decreases in performance or damage to the device. Two-phase cooling in microchannels has shown great promise in steady-state studies, dissipating heat fluxes over 1.1 kW cm-2. The very high latent heat and buoyancy-driven effects associated with two-phase cooling produce large heat transfer coefficients, minimizing undesirable temperature gradients across the diode. Previous research has primarily focused on steady-state operation. Although promising steady-state results were documented, little is known on the effects of transient heat loads on microchannel flow boiling. Laser diodes can rapidly change their optical output, inducing extreme transient heat loads. Furthermore, cold start up, where the diode is stepped up directly to maximum optical output, produce transient heat loads which are especially concerning. These transient challenges need to be fully understood to usefully implement two-phase cooling of laser diode arrays. The current study investigates the effects of transient heat loads on a multi-microchannel evaporator. A silicon multi-microchannel heat exchanger with small hydraulic diameters (52 µm) and a surrogate laser diode heater, developed by Lawrence Livermore National Laboratory, is integrated into a two-phase pumped loop to perform transient experiments with pulsed and ramped heat loads. When exposed to pulsed loads, infrared temperature measurements and flow visualization showed extreme superheat temperatures (~50°C) before the onset of boiling. After the onset of boiling, unexpected flow instabilities were seen, followed by a delay in steady-state two-phase boiling that could not be explained by thermal mass of the test section. Transients in the flow conditions were also documented, and ramping heat loads showed promise in mitigating the peak temperature and flow instabilities. Furthermore, a transient thermal suite (ATTMO) developed by P C Krause and Associates (PCKA), is utilized to model the microchannel evaporator. The thermal suite is augmented to model the dynamics seen under a pulsed heat load. A reduced-order, non-computationally demanding method using a logistic function to describe the transient heat transfer coefficient is implemented into ATTMO. The transient modeling results showed a good correlation (average error of (±2.04°C) with the experimental data collected. A direct relationship between onset of boiling temperature and growth rate is shown. The results from this study show potentially dangerous peak temperatures for laser diodes. Mitigation strategies should be investigated and implemented to avoid the extreme superheat temperatures. The non-computationally demanding model developed in this research can be used in future studies to rapidly investigate the effects of heat loads and different operational parameters
Evaluating the sustainability performance of U.S. biofuel in 2017 with an integrated techno-economic and life cycle assessment framework
No full textIncludes bibliographical references.2022 Fall.The United States produced more than 66.2 million m3 of biofuel for the transportation industry in 2017. Most of that volume (60.6 million m3) was produced in the form of corn ethanol and the majority of the remaining volume (4.2 million m3) was produced in the form of soybean-based biodiesel. Numerous works have assessed the economic and environmental performance of these two biofuel types. However, no work exists which evaluates both the economic and environmental outcomes of these two fuels with adequate geospatial resolution and national scope. In this study, a model framework is constructed that performs concurrent Techno-Economic Analysis (TEA) and Life Cycle Assessment (LCA) using high-resolution input datasets to provide a granular estimation of sustainability performance of every county in the United States. This work presents results that include sector wide estimates and highlights the importance of capturing geographic heterogeneity. Results show a total emission volume of 55 MMT CO2-eq produced by the 2017 US biofuel industry, with 7 MMT CO2-eq of that amount resulting from Land Use Change effects. Nationwide weighted mean Global Warming Potential results are 38 gCO2-eq/MJ and 37 gCO2-eq/MJ for corn ethanol and soybean biodiesel, respectively, when Land Use Change emissions are included. Minimum Fuel Selling Price results are 2.52/GGE) and 2.72/GGE) for corn ethanol and soybean biodiesel, respectively. A Zero-Emissions Cost (ZEC) metric is applied, which combines the economic and environmental performance of a fuel into its analysis. Specifically, the cost associated with offsetting all fuel production and use emissions through Direct Air Capture (DAC) is added to the standard price of the fuel. Mean ZEC results are 4.53/GGE) for corn ethanol and 4.69/GGE) for soybean biodiesel which are lower than the ZEC of conventional gasoline of 7.45/GGE). Finally, the cost of Direct Air Capture which results in ZEC parity between each biofuel and its petroleum-based counterpart is assessed to be $49/MT CO2-eq
An analysis of Internet of Things (IOT) ecosystem from the perspective of device functionality, application security and application accessibility
No full text2022 Spring.Includes bibliographical references.Internet of Thing (IoT) devices are being widely used in smart homes and organizations. IoT devices can have security vulnerabilities in different fronts: Device front with embedded functionalities and Application front. This work aims to analyze IoT devices security health from device functionality perspective and application security and accessibility perspective to understand holistic picture of entire IoT ecosystem's security health. An IoT device has some intended purposes, but may also have hidden functionalities. Typically, the device is installed in a home or an organization and the network traffic associated with the device is captured and analyzed to infer high-level functionality to the extent possible. However, such analysis is dynamic in nature, and requires the installation of the device and access to network data which is often hard to get for privacy and confidentiality reasons. In this work, we propose an alternative static approach which can infer the functionality of a device from vendor materials using Natural Language Processing (NLP) techniques. Information about IoT device functionality can be used in various applications, one of which is ensuring security in a smart home. We can also use the device functionalities in various security applications especially access control policies. Based on the functionality of a device we can provide assurance to the consumer that these devices will be compliant to the home or organizational policy even before they have been purchased. Most IoT devices interface with the user through mobile companion apps. Such apps are used to configure, update, and control the device(s) constituting a critical component in the IoT ecosystem, but they have historically been under-studied. In this thesis, we also perform security and accessibility analysis of IoT application on 265 apps to understand security and accessibility vulnerabilities present in the apps and identify some mitigating strategies
Sustainable recycling of metal machining swarf via spark plasma sintering
No full text2021 Fall.Includes bibliographical references.In general, extracting virgin metals from natural resources exerts a significant environmental and economic impact on our earth and society. Production of virgin stainless steels and titanium (Ti) alloys have particularly caused concerns because of the high demands of these two classes of metals across many industries, with low fractions of scraps (less than one-third for steels and one-fourth for Ti alloys) that are currently recirculated back into supply. In addition, the conventional recycling methods for metals require multiple steps and significant energy consumption. With the overarching goal of reducing energy consumption and streamlining recycling practices, the present research investigated the effectiveness of direct reuse of stainless steel swarf and Ti6Al-4V alloy swarf as feedstock for spark plasma sintering (SPS) to make solid bulk samples. The parts made from machining swarf were characterized to tackle material challenges associated with the metal swarf such as irregular shapes and a higher amount of oxygen content. The hypothesis was that while solid bulk parts made from metal swarf would contain undesired pores that degrade mechanical performance, some mechanical properties (e.g., hardness) can be comparable or even outperform the industrial standard counterparts made from virgin materials, because of cold working and grain refinement that occurred to the swarf during machining and the capability of SPS to retain ultrafine microstructures. 304L stainless steel and Ti-6Al-4V (Ti64) alloy swarf were collected directly from machining processes, cleaned, and then consolidated to bulk samples by SPS with or without addition of gas atomized powder. Nanoindentation and Vickers indentation were utilized to evaluate the hardness at two length scales. Ball milling was performed on Ti64 to assess the energy consumption required to effectively convert swarf to varied morphologies. In addition, to provide insight into the macroscale mechanical behavior of the materials made by SPS of recycled swarf, finite element modeling (FEM) was used to predict tensile stress-strain curves and the corresponding stress distributions in the samples. The key findings from my research proved that reuse of austenitic stainless steel chips and Ti64 alloy swarf as feedstock for SPS is an effective and energy efficient approach to recycle metal scraps, compared to the production and use of virgin gas atomized powders, or conventional metal recycling routes. The mechanical performance of the samples made from metal swarf outperformed the relevant industrial standard materials in terms of hardness while the ductility remains a concern due to the presence of pores. Therefore, future work is proposed to continue to address the challenges associated with mechanical performance, including but not limited to, tuning the SPS processing parameters, quantifying an appropriate amount of addition of powder as a sintering aid, and refining the morphology of the swarf by ball milling. It is critical for the health of our planet to always consider the tradeoff between energy consumption and materials performance
Techno-economic analysis of advanced small modular nuclear reactors
No full text2022 Summer.Includes bibliographical references.Small modular nuclear reactors (SMRs) represent a robust opportunity to develop low-carbon and reliable power with the potential to meet cost parity with conventional power systems. This study presents a detailed, bottom-up economic evaluation of a 12x77 MWe (924 MWe total) light-water SMR (LW-SMR) plant, a 4x262 MWe (1,048 MWe) gas-cooled SMR (GC-SMR) plant, and a 5x200 MWe (1,000 MWe total) molten salt SMR (MS-SMR) plant. Cost estimates are derived from equipment costs, labor hours, material inputs, and process-engineering models. The advanced SMRs are compared to natural gas combined cycle plants and a conventional large reactor. Overnight capital cost (OCC) and levelized cost of energy (LCOE) estimates are developed. The OCC of the LW-SMR, GC-SMR, and MS-SMR are found to be 4,355/kW, and 89.6/MWh, 80.6/MWh respectively. A Monte Carlo analysis is performed, for which the OCC and construction time of the LW-SMR is found to have a lower mean and standard deviation than a conventional large reactor. The LW-SMR OCC is found to have a mean of 658/kW and a 90% probability of remaining between 6,399/kW, while the construction duration is found to have a mean of 4.5 years with a standard deviation of 0.8 years and a 90% probability of remaining between 3.4 and 6.0 years. The economic impact of economies of scale, simplification, modularization, and construction time are evaluated for SMRs. Policy implications for direct capital subsidies and a carbon tax on natural gas emissions are additionally explored
Investigation of liquid cooling on M9506A high density Keysight AXIE chassis
No full text2021 Fall.Includes bibliographical references.Forced convection air-cooled heat sinks are the dominant cooling method used in the electronics industry, accounting for 86% of high-density cooling in data centers. However, the continual performance increases of electronics equipment are pushing these air-cooled methods to their limit. Fundamental limitations such as acoustics, cooling power consumption, and heat transfer coefficient are being reached while processor power consumption is steadily rising. In this study, a 4U, 5-slot, high density computing box is studied to determine the maximum heat dissipation in its form factor while operating at an ambient air temperature of 50°C. Two liquid cooling technologies were analyzed in this effort and compared against current state-of-the-art air-cooled systems. A new configuration proposed using return jet impingement with dielectric fluid FC72 directly on the integrated circuit die shows up to a 44% reduction in thermal resistance as compared to current microchannel liquid cooled systems, 0.08 K W-1, vs 0.144 K W-1, respectively. In addition, at high ambient temperatures (~45°C), the radiator of the liquid cooled system accounts for two thirds of the thermal resistance from ambient to junction temperature, indicating that a larger heat exchanger outside the current form factor could increase performance further. The efficiency of the chips was modeled with efficiency predictions based on their junction temperature. On a system level, the model showed that by keeping the chassis at 25°C ambient, the overall power consumption was significantly lower by 500W. Furthermore, the failure rate was accounted for when the chip junction temperature was beyond 75°C. FC72 jet impingement on the die showed the best performance to meet the system cooling requirements and kept the chips below 75°C for the highest ambient temperatures but consumed the most pumping power of all of the fluids and configurations investigated. The configuration with microchannels bypassing TIM 2 showed near the same performance as jet impingement with water on the lid and reduced the junction temperature difference by 5°C when compared to baseline. When the fluid was switched from water to a water glycol 50/50 mixture, an additional thermal resistance of 0.010 K W-1 was recorded at the heat sink level and a higher mass flow rate was required for the GC50/50 heat exchanger to achieve its minimum thermal resistance
Neural network security and optimization for single-person authentication using electroencephalogram data
No full textIncludes bibliographical references.2022 Fall.Security is an important focus for devices that use biometric data, and as such security around authentication needs to be considered. This is true for brain-computer interfaces (BCIs), which often use electroencephalogram (EEG) data as inputs and neural network classification to determine their function. EEG data can also serve as a form of biometric authentication, which would contribute to the security of these devices. Neural networks have also used a method known as ablation to improve their efficiency. In light of this info, the goal of this research is to determine whether neural network ablation can also be used as a method to improve security by reducing a network's learning capabilities to include authenticating only a given target, and preventing adversaries from training new data to be authenticated. Data on the change in entropy of weight values of the networks after training was also collected for the purpose of determining patterns in weight distribution. Results from a set of ablated networks to a set of baseline (non-ablated) networks for five targets chosen randomly from a data set of 12 people were compared. The results found that ablated maintained accuracy through the ablation process, but that they did not perform as well as the baseline networks. Change in performance between single-target authentication and target-plus-invader authentication was also examined, but no significant results were found. Furthermore, the change in entropy differed between both baseline networks and ablated networks, as well as between single-target authentication and target-plus-invader authentication for all networks. Ablation was determined to have potential for security applications that need to be expanded on, and weight distribution was found to have some correlation with the complexity of an input to a network
The manufacturing and soft robotic applications of free stroke twisted and coiled actuators
No full text2022 Spring.Includes bibliographical references.Inspired by biological systems (e.g., octopus), soft robots made from soft materials outperform traditional rigid robots in terms of safety and adaptivity because of their compliant and deformable bodies. To enable a soft robot's unique capabilities, they require a key component—the actuator. Many different actuators have been used, including the conventional pneumatic-driven and cable driven methods, and also several emerging approaches, like dielectric elastomers, liquid crystal elastomers, and shape memory alloys. Besides existing actuation approaches, another promising actuator for soft robots is the twisted-and-coiled actuator (TCA), which can be conveniently fabricated by continuously twisting polymer fibers into a coiled spring-like shape. In this thesis, we investigate free stroke TCAs (i.e., TCAs that can produce significant displacements without preloading). We first describe a customized machine that can automatically fabricate TCAs with free strokes by twisting a polymer fiber and then coiling the twisted fiber along a mandrel with a guide channel, which is made by wrapping a small copper wire helically about a larger one. After that, we discuss the characterization and evaluation of the fabricated TCAs. We also apply free stroke TCAs to two different soft robotic systems. The first one is a spherical tensegrity robot which resembles a tensegrity structure, a compliant yet stable structure made of rigid rods and elastic cables. By replacing the elastic cables with TCAs, we can actuate TCAs to shift the robot's center of gravity to generate rolling locomotion. The second application is a shape morphing quadrupedal robot with multiple modes of locomotion. By actively morphing the robot's body shape, we demonstrate different locomotion modes for the same robot, including walking on flat ground, crawling below a gap, and climbing across a bridge. Demonstrations for the tensegrity robot and shape morphing robot will facilitate future biologically inspired adaptive robotic systems to actively adapt their morphologies and behaviors to different environments
Systems engineering analysis and application to the Emergency Response System
No full text2021 Fall.Includes bibliographical references.This research seeks to apply systems engineering methods to build a more effective emergency response system (called the Engineered Emergency Response System – EERS) to minimize adverse impacts and consequences of incidents. Systems engineering processes were used to identify stakeholder needs and requirements, and then systems engineering methodologies were used to build the system. Emphasis was placed on building a more capable engineered system that could handle not only routine emergencies, but also events containing increased complexity, uncertainty, and severity. The resulting EERS system was built on suitability constraints including conformance to the National Response Framework, the National Incident Management System Framework, and the community fragility concept, as well as ease of transformation from the existing system. Empirical data from two complex events in Colorado's El Paso County, the Waldo Canyon Wildland Urban Interface fire in 2012 and the Black Forest Wildland Urban Interface fire in 2013, were used to inform the system's design and operation. These complex and dynamic events were deemed representative of other complex events based on existing publications and research. After the engineered system was built, it was validated: 1) using the Functional Dependency Network Analysis model with data obtained from the two fires, 2) evaluating best practices that were integrated into the EERS, 3) qualitatively assessing system suitability requirements, and 4) conducting a Delphi study to assess the value of applying systems engineering to this research area; and, the feasibility of implementing the EERS into existing systems. The validation provided evidence that the EERS is more effective than the existing system while showing that it is also suitable and feasible. The Delphi study provided evidence that using the systems engineering approach was deemed valuable by the subject matter experts. More research is needed to determine system needs and capabilities for specific communities in consideration of their unique organizations, cultures, environments, and associated hazards, and in areas of command and control and communications
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