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2007

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Articles 2071 - 2100 of 3831

Full-Text Articles in Engineering

Quantitative Regional Associations Between Remodeling, Modeling, And Osteocyte Apoptosis And Density In Rabbit Tibial Midshafts, Nicole L. Hedgecock, Tamer Hadi, Andrew A. Chen, Shane B. Curtiss, R. Bruce Martin, Scott J. Hazelwood Mar 2007

Quantitative Regional Associations Between Remodeling, Modeling, And Osteocyte Apoptosis And Density In Rabbit Tibial Midshafts, Nicole L. Hedgecock, Tamer Hadi, Andrew A. Chen, Shane B. Curtiss, R. Bruce Martin, Scott J. Hazelwood

Biomedical Engineering

Evidence suggests that osteocyte apoptosis is involved in the adaptive response of bone, although the specific role of osteocytes in the signaling mechanism is unknown. Here, we examined and correlated regional variability in indices of remodeling, modeling, osteocyte apoptosis, and osteocyte density in rabbit tibia midshafts. Histomorphometric analysis indicated that remodeling parameters (BMU activation frequency, osteon density, forming osteon density, and resorption cavity density) were lower in the cranial region compared to other quadrants. In addition, pericortical subregions displayed less remodeling relative to intracortical and endocortical ones. Modeling indices also demonstrated regional variability in that periosteal surfaces exhibited a greater …

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Issues In Front-End Engineering Of Cmos Nanoelectronics, Xiaolong Yang Mar 2007

Issues In Front-End Engineering Of Cmos Nanoelectronics, Xiaolong Yang

Electrical Engineering Dissertations - Archive

Several issues exist in current CMOS front-end engineering such as interfacial layer formation at high-k/Si interface, high metal/Si contact resistance in source and drain regions, and absence of a quantitative model for silicon-germanium alloy growth. In this dissertation, monolayer Se passivation is employed to create a Si (100) surface free of dangling bonds. Since dangling bonds are the origins of surface reaction sites and surface states, interfacial layer formation at high-k/Si interface can be suppressed and metal/Si contact resistance can be lowered by Se passivation. Firstly, results on interface engineering between HfO2 and n-type Si (100) with Se passivation are …

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Sensitivity Of A Distributed Watershed Simulation Model To Spatial Scale, Misgana K. Muleta, John W. Nicklow, Elias G. Bekele Mar 2007

Sensitivity Of A Distributed Watershed Simulation Model To Spatial Scale, Misgana K. Muleta, John W. Nicklow, Elias G. Bekele

Civil and Environmental Engineering

The results of distributed watershed models could be sensitive to spatial and temporal scales at which inputs and model parameters are aggregated. This paper reports findings of a detailed sensitivity analysis conducted on the U.S. Department of Agriculture’s distributed watershed simulation model, known as the Soil and Water Assessment Tool (SWAT). The Big Creek Watershed, located in southern Illinois, is used for the study. The model is calibrated to improve accuracy of its streamflow and sediment concentration predictions using observed data at two locations in the study watershed. Streamflow and sediment concentrations that are simulated by the calibrated model at …

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Centerline Curbing Treatment At Railroad Crossings For Improved Safety, Aemal Khattak, Dwight L. Mosby Jr., Gregory Mcknight, Brian Gardner Mar 2007

Centerline Curbing Treatment At Railroad Crossings For Improved Safety, Aemal Khattak, Dwight L. Mosby Jr., Gregory Mcknight, Brian Gardner

Nebraska Department of Transportation: Research Reports

The objectives of this research were to study unsafe actions of motor vehicle drivers at railroadhighway grade crossings, to evaluate centerline barriers in reducing those unsafe driver actions, and to note any maintenance or other issues with the barriers. Driver actions were observed at two railroad crossings before and after installation of centerline barriers. A comparison of observed driver actions in the pre- and post-barrier periods provided information on the effectiveness of the barriers in reducing unsafe driver actions while periodic inspection of the centerline barriers provided information on maintenance needs. A major concern of the Nebraska Department of Roads …

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Medical Diagnostic Ultrasound, E. Carr Everbach Mar 2007

Medical Diagnostic Ultrasound, E. Carr Everbach

Engineering Faculty Works

As early as 250 BCE, captains of ancient Greek ships would drop lead weights overboard to provide an estimate of water depth. They would count until those “sounders” produced an audible thud and in that way measure the propagation time of the falling weight. Even though the practice has given way to other technologies for sounding, one still hears the phrase “to sound something out.” In the 17th century, Isaac Newton became fascinated with sound propagation and was one of the first to describe relationships between the speed of sound and measurable properties of the propagation medium, such as density …

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Lightweight Error Correction Coding For System-Level Interconnects, Jason D. Bakos, Donald M. Chiarulli, Steven P. Levitan Mar 2007

Lightweight Error Correction Coding For System-Level Interconnects, Jason D. Bakos, Donald M. Chiarulli, Steven P. Levitan

Faculty Publications

"Lightweight hierarchical error control coding (LHECC)" is a new class of nonlinear block codes that is designed to increase noise immunity and decrease error rate for high-performance chip-to-chip and on-chip interconnects. LHECC is designed such that its corresponding encoder and decoder logic may be tightly integrated into compact, high-speed, and low-latency I/O interfaces. LHECC operates over a new channel technology called multi-bit differential signaling (MBDS). MBDS channels utilize a physical-layer channel code called "N choose M (nCm)" encoding, where each channel is restricted to a symbol set such that half of the bits in each symbol are set to one. …

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Bs News Mar 2007

Bs News

Building Services Engineering

No abstract provided.

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Peer Review Of Teaching Project, Paul Savory, Amy M. Goodbrun, Amy Nelson Burnett Mar 2007

Peer Review Of Teaching Project, Paul Savory, Amy M. Goodbrun, Amy Nelson Burnett

Department of Industrial and Management Systems Engineering: Faculty Publications

The national impact of UNL’s Peer Review of Teaching Project was recognized in 2005 – with a TIAA-CREF Hesburgh Certificate of Excellence – as an exceptional program in enhancing undergraduate student learning. In 2006, the project was designated an Institutional Leader by the Carnegie Foundation for the Advancement of Teaching and Learning. As a national institutional leader, the project will continue defining, measuring, tracking, and improving approaches that deepen student understanding.

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Creating An Internet Repository For Course Portfolios, Paul Savory, Amy M. Goodburn, Amy Nelson Burnett Mar 2007

Creating An Internet Repository For Course Portfolios, Paul Savory, Amy M. Goodburn, Amy Nelson Burnett

Department of Industrial and Management Systems Engineering: Faculty Publications

Our ITLE grant has supported the development of www.courseportfolio.org – an internet repository for faculty-written course portfolios documenting best practices and evidence of student learning occurring in the classroom.

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Crop Residue Effects On Runoff Nutrient Concentrations Following Manure Application, Jeffrey E. Nicolaisen, John E. Gilley, Bahman Eghball, David B. Marx Mar 2007

Crop Residue Effects On Runoff Nutrient Concentrations Following Manure Application, Jeffrey E. Nicolaisen, John E. Gilley, Bahman Eghball, David B. Marx

Department of Agricultural and Biological Systems Engineering: Faculty Publications

Manure is applied to cropland areas managed under diverse conditions, resulting in varying amounts of residue cover. The objective of this study was to measure the effects of crop residue on nutrient concentrations in runoff from areas where beef cattle or swine manure were recently applied but not incorporated. Plots 0.75 m wide by 2 m long were established at the study site. Existing residue materials were removed, and corn, soybean, or winter wheat residue was added at rates of 2, 4, or 8 Mg ha−1. Manure was then applied at rates required to meet estimated annual nitrogen …

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Lake Roosevelt Water Quality And Hydrodynamic Model Calibration With Fish Bioenergetics, Michael Lee Mckillip Mar 2007

Lake Roosevelt Water Quality And Hydrodynamic Model Calibration With Fish Bioenergetics, Michael Lee Mckillip

Civil and Environmental Engineering Faculty Publications and Presentations

An understanding of the effects of hydrodynamics and reservoir operations on the Franklin D. Roosevelt Lake (Lake Roosevelt) aquatic food web allows for better management of the reservoir. A CE-QUAL-W2, v.3.5, hydrodynamic and water quality model (Cole and Wells, 20061) is being applied to the reservoir. The models zooplankton algorithms are expanded and a fish bioenergetics model is incorporated. The Lake Roosevelt model extent is shown in Figure 1. The model includes the lacustrine arms up to full pool on the Sanpoil, Kettle, and Colville Rivers; the Spokane River arm up to Little Falls Dam; and the Columbia River from …

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A Value-Focused Thinking Model For The Selection Of The Best Rigid Pavement, Partial-Depth Spall Repair Material, Benjamin G. Speer Mar 2007

A Value-Focused Thinking Model For The Selection Of The Best Rigid Pavement, Partial-Depth Spall Repair Material, Benjamin G. Speer

Theses and Dissertations

Concrete spalls on airfield pavements generate foreign object debris (FOD) that is damaging to aircraft engines, and may damage landing gear by roughening of the pavement surface. Repairing spalled concrete on aging and deteriorating airfields is essential for its safe operational use. Picking the best repair material from many products on the commercial market is difficult. There is wide variation on material properties, and good performance on certain criteria is critical to constructing long lasting repairs. Since there is currently no procedure for Air Force decision-makers to select the best rigid-pavement repair material, a model was created using Value-Focused Thinking …

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Analyzing The Interdiction Of Sea-Borne Threats Using Simulation Optimization, Kristen L. Cavallaro Mar 2007

Analyzing The Interdiction Of Sea-Borne Threats Using Simulation Optimization, Kristen L. Cavallaro

Theses and Dissertations

Worldwide, maritime trade accounts for approximately 80% of all trade by volume and is expected to double in the next twenty years. Prior to September 11, 2001, Ports, Waterways and Coastal Security (PWCS) was afforded only 1 percent of United States Coast Guard (USCG) resources. Today, it accounts for nearly 22 percent of dedicated USCG resources. Tactical assessment of resource requirements and operational limitations on the PWCS mission is necessary for more effective management of USCG assets to meet the broader range of competing missions. This research effort involves the development and validation of a discrete-event simulation model of the …

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Performance Evaluation Of Ad Hoc Routing In A Swarm Of Autonomous Aerial Vehicles, Matthew T. Hyland Mar 2007

Performance Evaluation Of Ad Hoc Routing In A Swarm Of Autonomous Aerial Vehicles, Matthew T. Hyland

Theses and Dissertations

This thesis investigates the performance of three mobile ad hoc routing protocols in the context of a swarm of autonomous unmanned aerial vehicles (UAVs). It is proposed that a wireless network of nodes having an average of 5.1774 log n neighbors, where n is the total number of nodes in the network, has a high probability of having no partitions. By decreasing transmission range while ensuring network connectivity, and implementing multi-hop routing between nodes, spatial multiplexing is exploited whereby multiple pairs of nodes simultaneously transmit on the same channel. The proposal is evaluated using the Greedy Perimeter Stateless Routing (GPSR), …

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Analysis Of Routing Worm Infection Rates On An Ipv4 Network, James Gorsuch Mar 2007

Analysis Of Routing Worm Infection Rates On An Ipv4 Network, James Gorsuch

Theses and Dissertations

Malicious logic, specifically worms, has caused monetary expenditure problems to network users in the past. Worms, like Slammer and Code Red, have infected thousands of systems and brought the Internet to a standstill. This research examines the ability of the original Slammer worm, the Slammer based routing worm proposed by Zou et al, and a new Single Slash Eight (SSE) routing worm proposed by this research to infect vulnerable systems within a given address space. This research investigates the Slammer worm's ability to generate a uniform random IP addresses in a given address space. Finally, a comparison of the speed …

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Experimental Methods To Characterize Nonlinear Vibration Of Flapping Wing Micro Air Vehicles, Adam P. Tobias Mar 2007

Experimental Methods To Characterize Nonlinear Vibration Of Flapping Wing Micro Air Vehicles, Adam P. Tobias

Theses and Dissertations

For urban combat reconnaissance, the flapping wing micro air vehicle concept is ideal because of its low speed and miniature size, which are both conducive to indoor operations. The focus of this research is the development of experimental methods best suited for the vibration testing of the wing structure of a flapping wing micro air vehicle. This study utilizes the similarity of a beam resonating at its first bending mode to actual wing flapping motion. While computational finite element analysis based on linear vibration theory is employed for preliminary beam sizing, an emphasis is placed on experimental measurement of the …

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Investigating Optimal Capacity Scalability Scheduling In A Reconfigurable Manufacturing System, Ahmed M. Deif, Waguih Elmaraghy Mar 2007

Investigating Optimal Capacity Scalability Scheduling In A Reconfigurable Manufacturing System, Ahmed M. Deif, Waguih Elmaraghy

Industrial Technology and Packaging

Responsiveness to dynamic market changes in a cost-effective manner is becoming a key success factor for any manufacturing system in today’s global economy. Reconfigurable manufacturing systems (RMSs) have been introduced to react quickly and effectively to such competitive market demands through modular and scalable design of the manufacturing system on the system level, as well as on the machine components’ level. This paper investigates how RMSs can manage their capacity scalability on the system level in a cost-effective manner. An approach for modeling capacity scalability is proposed, which, unlike earlier approaches, does not assume that the capacity scalability is simply …

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Sampled-Data Kalman Filtering And Multiple Model Adaptive Estimation For Infinite-Dimensional Continuous-Time Systems, Scott A. Sallberg Mar 2007

Sampled-Data Kalman Filtering And Multiple Model Adaptive Estimation For Infinite-Dimensional Continuous-Time Systems, Scott A. Sallberg

Theses and Dissertations

Kalman filtering and multiple model adaptive estimation (MMAE) methods have been applied by researchers in several engineering disciplines to a multitude of problems featuring a linear (or mildly nonlinear) model based on finite-dimensional differential (or difference) equations perturbed by random inputs. However, many real-world systems are more naturally modeled using an infinite-dimensional continuous-time linear systems model, such as those most naturally modeled as partial differential equations or time-delayed differential equations along with a possibly infinite-dimensional measurement model. The Kalman filtering technique was extended to encompass infinite-dimensional continuous-time systems with sampled-data measurements and a technique to approximate an infinite-dimensional continuous-time system …

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Dynamic Response Of A Collidant Impacting A Low Pressure Airbag, Peter A. Dreher Mar 2007

Dynamic Response Of A Collidant Impacting A Low Pressure Airbag, Peter A. Dreher

Theses and Dissertations

There are many uses of low pressure airbags, both military and commercial. Many of these applications have been hampered by inadequate and inaccurate modeling tools. This dissertation contains the derivation of a four degree-of-freedom system of differential equations from physical laws of mass and energy conservation, force equilibrium, and the Ideal Gas Law. Kinematic equations were derived to model a cylindrical airbag as a single control volume impacted by a parallelepiped collidant. An efficient numerical procedure was devised to solve the simplified system of equations in a manner amenable to discovering design trends. The largest public airbag experiment, both in …

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Diffusion Of Innovation: Factors Promoting Interest In Solar Photovoltaic Generation Systems Within Air Force Installations, Daniel Diaz Jr. Mar 2007

Diffusion Of Innovation: Factors Promoting Interest In Solar Photovoltaic Generation Systems Within Air Force Installations, Daniel Diaz Jr.

Theses and Dissertations

The purpose of this research was to identify factors which promote interest in solar photovoltaic generation systems for facility use within the United States Air Force. The construct model was developed based on past literature on Diffusion of Innovation Theory. The model comprised of measures defined as motivation, knowledge, experience, and familiarity as well as contextual variables. These measures were then used to determine whether any significant association existed between the measures and the overall dependent variable, interest. A phone interview was conducted on Air Force energy managers located within the continental U.S. The methods of correlation and regression analysis …

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Experimental Investigation Of Oblique Wing Aerodynamics At Low Speed, Matthew J. Dillsaver Mar 2007

Experimental Investigation Of Oblique Wing Aerodynamics At Low Speed, Matthew J. Dillsaver

Theses and Dissertations

In an effort to increase the range of missiles and guided bombs, the USAF is looking at options for new wing configurations. One such configuration being considered is oblique wings. An oblique wing is a wing that pivots about a point on the aircraft fuselage thereby having one side swept forward and the other swept aft. Additional interest is looking at a wing only configuration that also rotates with one wing tip forward of the other. Studies have shown that this configuration can provide less drag for a given lift at both supersonic cruise and subsonic loiter conditions. This experiment …

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Demonstration Of Clean Particle Seeding For Particle Image Velocimetry In A Closed Circuit Supersonic Wind Tunnel, Charles M. Mcniel Mar 2007

Demonstration Of Clean Particle Seeding For Particle Image Velocimetry In A Closed Circuit Supersonic Wind Tunnel, Charles M. Mcniel

Theses and Dissertations

The purpose of this research was to determine whether solid carbon dioxide (CO2) particles might provide a satisfactory, and cleaner, alternative to traditional seed material for Particle Image Velocimetry (PIV) for use in a closed circuit supersonic wind tunnel. The Air Force Institute of Technology (AFIT) closed circuit pressure-vacuum supersonic wind tunnel was utilized, which achieves a nominal Mach number of Mach 2.9 in a 2.5 inch by 2.5 inch square test section. CO2 was dispensed into the flow as a liquid from a standard compressed gas liquid tank through two different injector styles at two injection …

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Finite Element Solution: Nonlinear Flapping Beams For Use With Micro Air Vehicle Design, Robert L. Walker Mar 2007

Finite Element Solution: Nonlinear Flapping Beams For Use With Micro Air Vehicle Design, Robert L. Walker

Theses and Dissertations

The development and use of Micro Air Vehicles is becoming more and more important to the military. Size, weight, maneuverability, stealth, and fuel consumption are just some of the constraints on a future Micro Air Vehicle. Perfect blueprints for a small scale flying machine are both insects and humming birds. Medium sized hummingbirds are found to have wings-beats at a frequency of 18-28 Hz. There is a vast amount of complexity to just how these creatures can create lift; however, this study looks at different beams made of common materials with 1st natural bending frequencies in this range. This study …

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Three Dimensional Analysis Of A Composite Repair And The Effect Of Overply Shape Variation On Structural Efficiency, David A. Sutter Mar 2007

Three Dimensional Analysis Of A Composite Repair And The Effect Of Overply Shape Variation On Structural Efficiency, David A. Sutter

Theses and Dissertations

This research characterizes, in the elastic range, a scarf joint with overply using digital image correlation photogrammetry and finite element modeling. Additionally, the effect of varying the overply's geometric profile is examined. Specimens are constructed from AS4/3501-6 prepreg with a [0±45/90]2S layup. A fixture is used to achieve a consistent scarfed hole in each panel. The patch and adhesive (FM 300) are co-cured to the panels using positive pressure, which minimizes repair porosity. Three variations in the overply geometry are used: circular, rooftop-end, and tooth-end. The full strain field in each uni-axially loaded specimen is captured using digital image …

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Optimal Control Of A Circulare Satellite Formation Subject To Gravitational Perturbations, Jason L. Baldwin Mar 2007

Optimal Control Of A Circulare Satellite Formation Subject To Gravitational Perturbations, Jason L. Baldwin

Theses and Dissertations

Satellite formations, otherwise known in the space community as satellite clusters or distributed satellite systems, have been studied extensively over the last 10 to 15 years. For use in remote sensing applications, formations consisting of smaller, simpler satellites provide numerous advantages over individual satellites. The image resolution capabilities of small-satellite formations constitute a significant technological leap in the ability to synthesize critical information. This research utilizes the nonlinear satellite dynamics, including gravitational perturbations, to search for the optimal fuel cost for maintaining a circular formation. The system dynamics were developed in an earth-centered inertial coordinate frame using the methods of …

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Lamb Wave Propagation In Varying Thermal Environments, Jennifer P. Andrews Mar 2007

Lamb Wave Propagation In Varying Thermal Environments, Jennifer P. Andrews

Theses and Dissertations

During flight, launch, and reentry, external surfaces on aerospace vehicles undergo extreme thermo-acoustic loads resulting in structural degradation. Structural health monitoring techniques are being devised to evaluate the health of these structures by locating and quantifying structural damage during and after flight. One such technique uses Lamb wave propagation to assess damage on the surface and through the thickness of thin materials. The objective of this study was to assess the sensitivity of piezo-generated Lamb wave propagation to isothermal and thermal gradient environments using both theoretical and experimental methods. Experimental isothermal tests were conducted over a temperature range of 0-225 …

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The Effects Of Microstructure On Fretting Fatigue Behavior Of Nickel Alloy In-100, Erik C. Saladin Mar 2007

The Effects Of Microstructure On Fretting Fatigue Behavior Of Nickel Alloy In-100, Erik C. Saladin

Theses and Dissertations

This thesis studied the effect of microstructure on the fretting fatigue behavior of IN-100. First, fretting and plain fatigue S-N curves were determined over a large range of applied stress at an identical R-ratio and for fretting tests, done with a constant contact load. It was found that fretting fatigue reduces the cycles to failure compared to plain fatigue. The half contact width was found for the specimens, the crack initiation angle was found to be 40 deg and the crack initiation location was at the trailing edge of contact for the fretting specimens. Computational work included finding the stress …

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Selecting Electricity Generation Sources In Remote Locations, Kelly E. Kwan Mar 2007

Selecting Electricity Generation Sources In Remote Locations, Kelly E. Kwan

Theses and Dissertations

The purpose of this research was to investigate the impact of using a decision analysis technique for the selection of an electrical generation system for remote locations. Specifically, this thesis sought to answer five research questions addressing the types of energy sources used in remote locations, the decision-making processes used to identify these sources, the types of constraints incorporated in such a process, other valued factors, and their level of importance in relation to each other. The research questions were answered through a comprehensive literature review and the 10-Step Value-Focused Thinking Process on a specific case study in the National …

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Using Value-Focused Thinking To Evaluate The Use Of Innovative Stormwater Management Technologies On Air Force Installations, Jeffrey T. Falcone Mar 2007

Using Value-Focused Thinking To Evaluate The Use Of Innovative Stormwater Management Technologies On Air Force Installations, Jeffrey T. Falcone

Theses and Dissertations

Stormwater runoff occurs naturally after every storm event; however, traditional development practices have created many impervious surfaces, such as buildings, parking lots, and streets that increase runoff volume and flow rate. Conventional stormwater management practices focus on collecting runoff into centralized channels and conveying it as quickly as possible to local bodies of water. This type of conveyance system decreases the opportunity for stormwater to naturally infiltrate back into the ground. It also prevents contaminants from being naturally filtered out of stormwater flows. As a result, centralized conveyance systems can cause flooding, erosion, and terrestrial and aquatic habitat degradation. Innovative …

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Recommendations For A Standardized Program Management Office (Pmo) Time Compliance Network Order (Tcno) Patching Process, Michael Czumak Iii Mar 2007

Recommendations For A Standardized Program Management Office (Pmo) Time Compliance Network Order (Tcno) Patching Process, Michael Czumak Iii

Theses and Dissertations

Network security is a paramount concern for organizations utilizing computer technology, and the Air Force is no exception. Network software vulnerability patching is a critical determinant of network security. The Air Force deploys these patches as Time Compliance Network Orders (TCNOs), which together with associated processes and enforced timelines ensure network compliance. While the majority of the network assets affected by this process are Air Force owned and operated, a large number are maintained by external entities known as Program Management Offices (PMOs). Although these externally controlled systems provide a service to the Air Force and reside on its network, …

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