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Stability Analysis Of A More General Class Of Systems With Delay-Dependent Coefficients, Chi Jin, Keqin Gu, Islam Boussaada, Silviu-Iulian Niculescu 2019 Laboratoire des Signaux et Syst`emes (L2S) CentraleSup´elec-CNRS-Universit´e Paris Sud, 3 rue Joliot- Curie 91192 Gif-sur-Yvette cedex, France.

Stability Analysis Of A More General Class Of Systems With Delay-Dependent Coefficients, Chi Jin, Keqin Gu, Islam Boussaada, Silviu-Iulian Niculescu

SIUE Faculty Research, Scholarship, and Creative Activity

This paper presents a systematic method to analyse the stability of systems with single delay in which the coefficient polynomials of the characteristic equation depend on the delay. Such systems often arise in, for example, life science and engineering systems. A method to analyze such systems was presented by Beretta and Kuang in a 2002 paper, but with some very restrictive assumptions. This work extends their results to the general case with the exception of some degenerate cases. It is found that a much richer behavior is possible when the restrictive assumptions are removed. The interval of interest for the ...


The Effect Of Flinak Molten Salt Corrosion On The Hardness Of Hastelloy N, David Kok 2019 Olivet Nazarene University

The Effect Of Flinak Molten Salt Corrosion On The Hardness Of Hastelloy N, David Kok

Scholar Week 2016 - present

The Molten Salt Reactor (MSR) has been identified as a promising candidate to replace aging nuclear reactors around the world. However, a suitable combination of molten salt and container material needs to be found in order to reduce the potential for corrosion in the MSR before it can be considered commercially viable. FLiNaK molten salt and the nickel-based alloy Hastelloy N have been identified as prime candidates for this function, but the severity of FLiNaK corrosion in Hastelloy N requires additional study before this combination can be used in the operation of a MSR. In this study, Hastelloy N samples ...


Influence Of Linear Reciprocating And Multi-Directional Sliding On Peek Wear Performance And Transfer Film Formation, Kevin A. Laux, Christian J. Schwartz 2019 Texas A&M University

Influence Of Linear Reciprocating And Multi-Directional Sliding On Peek Wear Performance And Transfer Film Formation, Kevin A. Laux, Christian J. Schwartz

Christian Schwartz

Because of their light weight, chemical resistance, and self-lubricating properties, polymers are used in applications ranging from biomedical to aerospace. Some polymers exhibit significant differences in wear resistancebased on whether they are in unidirectional or multidirectional sliding. Shear induced polymer chain orientation is believed to be responsible for this behavior. Polyetheretherketone (PEEK) has excellent wear resistance, but its multidirectional sliding behavior has not been thoroughly investigated. A factorial multidirectional pin-on-plate wear study of PEEK was conducted with a focus on molecular weight and sliding path directionality. These factors were studied for their correlation to over all wear performance. Additionally ...


Surface Layer Plastic Deformation As A Mechanism For Uhmwpe Wear, And Its Role In Debris Size., Kevin G. Plumlee, Christian J. Schwartz 2019 Oklahoma Christian University

Surface Layer Plastic Deformation As A Mechanism For Uhmwpe Wear, And Its Role In Debris Size., Kevin G. Plumlee, Christian J. Schwartz

Christian Schwartz

Ultra-high molecular weight polyethylene (UHMWPE) remains the primary bearing material for use in artificial joints, but the longevity of these implants is still hindered by an osteolytic immune system response initiated by sub-micron sized wear debris released from the UHMWPE bulk component. Studies have shown that the severity of the immune system response is linked to particle size. Current treatments for reducing this effect focus on reducing the total volume of wear, but do not directly address particle size due to a limited understanding of the mechanisms involved in producing such small debris. Directly observing these mechanisms is inherently challenging ...


Effects Of Contact Pressure, Molecular Weight, And Supplier On The Wear Behavior And Transfer Film Of Polyetheretherketone (Peek), Kevin A. Laux, Christian J. Schwartz 2019 Texas A&M University

Effects Of Contact Pressure, Molecular Weight, And Supplier On The Wear Behavior And Transfer Film Of Polyetheretherketone (Peek), Kevin A. Laux, Christian J. Schwartz

Christian Schwartz

Polyetheretherketone (PEEK) is a designation given to materials of the polyaryletherketone family having a characteristic distribution of ether and ketone groups in the polymer backbone. PEEK materials have high strength and chemical resistance as well as very high melting points and glass transition temperatures. Because of this combination of properties, PEEK materials find use for wear application in extreme environments where they provide a light-weight and corrosion resistant bearing material that often does not require lubrication. This study focused on determining the effects of supplier and molecular weight on the wear of particular PEEK materials, in addition to the effect ...


Numerical Investigation Of Inclination On The Thermal Performance Of Porous Fin Heatsink Using Pseudospectral Collocation Method, George Oguntala, Gbeminiyi Sobamowo, Raed Abd-Alhameed, James Noras 2019 University of Bradford

Numerical Investigation Of Inclination On The Thermal Performance Of Porous Fin Heatsink Using Pseudospectral Collocation Method, George Oguntala, Gbeminiyi Sobamowo, Raed Abd-Alhameed, James Noras

Karbala International Journal of Modern Science

Numerical investigation of inclination effect on the thermal performance of a porous fin heat sink is presented. The developed thermal model is solved using pseudo-spectral collocation method (PSCM). Parametric studies are carried out using PSCM, and the thermal characterization of heat sink with the inclined porous fin of rectangular geometry is presented. Results show that heat sink of inclined porous fin exhibits higher thermal performance than heat sink of vertical porous fin operating under the same thermal conditions with the same geometrical configurations. Performance of inclined or tilted fin increases with decrease in length-thickness aspect ratio. However, increase in the ...


Analysis Of Dynamic Behaviour Of A Tensioned Carbon Nanotube In Thermal And Pressurized Environments, Ahmed Yinusa, Gbeminiyi Sobamowo 2019 University of Lagos

Analysis Of Dynamic Behaviour Of A Tensioned Carbon Nanotube In Thermal And Pressurized Environments, Ahmed Yinusa, Gbeminiyi Sobamowo

Karbala International Journal of Modern Science

In this paper, the dynamic behaviour of a tensioned single-walled carbon nanotubes (SWCNT) in thermal and pressurized environments is investigated analytically. With the applications of Bernoulli-Euler and thermal elasticity mechanics theories, the governing equation of motion are developed and solved using Laplace and Fourier transforms. The results of the close form solution in this work are in excellent agreements with past results in literature. From the parametric studies, it is established that as the magnitude of the pressure distribution at the surface increases, the deflection associated with the nanotube increases at any mode of vibration. However, a corresponding increase in ...


Placenta‐On‐A‐Chip: In Vitro Study Of Caffeine Transport Across Placental Barrier Using Liquid Chromatography Mass Spectrometry, Rajeendra L. Pemathilaka, Jeremy D. Caplin, Saurabh S. Aykar, Reza Montazami, Nicole N. Hashemi 2019 Iowa State University

Placenta‐On‐A‐Chip: In Vitro Study Of Caffeine Transport Across Placental Barrier Using Liquid Chromatography Mass Spectrometry, Rajeendra L. Pemathilaka, Jeremy D. Caplin, Saurabh S. Aykar, Reza Montazami, Nicole N. Hashemi

Nicole N. Hashemi

Due to the particular structure and functionality of the placenta, most current human placenta drug testing methods are limited to animal models, conventional cell testing, and cohort/controlled testing. Previous studies have produced inconsistent results due to physiological differences between humans and animals and limited availability of human and/or animal models for controlled testing. To overcome these challenges, a placenta‐on‐a‐chip system is developed for studying the exchange of substances to and from the placenta. Caffeine transport across the placental barrier is studied because caffeine is a xenobiotic widely consumed on a daily basis. Since a fetus ...


Skin Tribology Phenomena Associated With Reading Braille Print: The Influence Of Cell Patterns And Skin Behavior On Coefficient Of Friction, Matthew A. Darden, Christian J. Schwartz 2019 Iowa State University

Skin Tribology Phenomena Associated With Reading Braille Print: The Influence Of Cell Patterns And Skin Behavior On Coefficient Of Friction, Matthew A. Darden, Christian J. Schwartz

Christian Schwartz

Efficient transmission of tactile information is vital for individuals who rely on their sense of touch to interact with and navigate their surroundings, including visually impaired persons. Somatosensory phenomena have been investigated with respect to surface topologies and neuron sensitivities in the skin, but there is little knowledge of the specific skin tribology when reading tactual-coded information such as braille. Braille is a tactual code that employs raised dome-shaped dots in six-position cells (2 columns by 3 rows per cell), with various dot patterns representing individual text characters, punctuation or mathematical operators. Due to the hypothesized significance of friction on ...


Parametric Investigation Of Soft-Body Penetration Into Parallel-Ridged Textured Surfaces For Tactile Applications, Thomas J. Wilde, Christian J. Schwartz 2019 Iowa State University

Parametric Investigation Of Soft-Body Penetration Into Parallel-Ridged Textured Surfaces For Tactile Applications, Thomas J. Wilde, Christian J. Schwartz

Christian Schwartz

The tribological interactions between skin and textured surfaces has profound impact on both the tactile perception of the product being used, as well as the functionality of the product with regards to friction coefficient. Previous work has shown that parallel-ridged textures have vastly different friction coefficients with regards to the direction of skin sliding, and that penetration of the skin into the voids between ridges not only add contact area but also potential for interlocking. The ability to model skin penetration into textural elements would prove to be very useful for predicting friction; however, the mechanics of the problem are ...


Microwave Self-Healing Technology As Airfield Porous Asphalt Friction Course Repair And Maintenance System, Amir Tabakovic, Declan O'Prey, Drew McKenna, David Woodward 2019 Technological University Dublin

Microwave Self-Healing Technology As Airfield Porous Asphalt Friction Course Repair And Maintenance System, Amir Tabakovic, Declan O'Prey, Drew Mckenna, David Woodward

Articles

A problem increasingly faced by airport authorities is the maintenance of runways. Due to their large aircraft loadings associated with take-off and landing operations, runways experience surface deterioration. Poor quality runway surfaces cannot be tolerated in such an environment. Maintenance issues must be carried out to maximise safety and minimise the risk of aircraft damage. A recent development has been the introduction of self-healing technologies such as rejuvenator encapsulation, induction and microwave heating to address these issues. This paper summarises a laboratory investigation to determine the effectiveness of microwave self-healing for crack repair of Porous Friction Course (PFC) used for ...


Investigation Of Friction Mechanisms In Finger Pad Sliding Against Surfaces Of Varying Roughness, Geetha Chimata, Christian J. Schwartz 2019 Iowa State University

Investigation Of Friction Mechanisms In Finger Pad Sliding Against Surfaces Of Varying Roughness, Geetha Chimata, Christian J. Schwartz

Christian Schwartz

Human finger pad friction and the effects of surface features on the fingerprint ridges, shape of the finger and the material properties of the finger were investigated. The friction coefficients for three fine-grit abrasive papers were measured to assess these effects. Four probing surfaces were used: human index finger pad, silicone replicas of the finger with and without fingerprints, and a smooth silicone sphere. Friction tests were performed at a constant normal load of 0.5 N in two probe orientations: normal and perpendicular to the orientation of the fingerprint ridges. Scanning electron microscopy of the abrasive papers was performed ...


Investigation Of The Effect Of The Normal Load On The Incidence Of Friction Blisters In A Skin-Simulant Model, Geetha Chimata, Christian J. Schwartz 2019 Iowa State University

Investigation Of The Effect Of The Normal Load On The Incidence Of Friction Blisters In A Skin-Simulant Model, Geetha Chimata, Christian J. Schwartz

Christian Schwartz

A laminar skin simulant was constructed to study the incidence of friction blisters. The skin simulant consists of a thin polyurethane top layer and textured gum foam rubber bottom layer adhered to an acrylic-backing plate to emulate the layered structure of the human skin. Friction blisters were produced on the skin simulant by using a dual-axis tribometer. The effect of the applied normal load on the number of cycles required to produce a blister was investigated. The skin simulant was also analyzed as an adhesive-bonded laminar composite to determine the relationship between the applied normal load and the number of ...


A New Analytical Evaluation Model For Kanban Controlled Systems With Fork/Join Synchronization Stations, Heedong Kim, Sarah M. Ryan 2019 Iowa State University

A New Analytical Evaluation Model For Kanban Controlled Systems With Fork/Join Synchronization Stations, Heedong Kim, Sarah M. Ryan

Sarah M. Ryan

A nonlinear programming model is developed for analyzing the queuing model of a kanban controlled system with fork/join synchronization stations. The model finds the minimum number of kanbans for a given throughput requirement or the maximum throughput for a given number of kanbans, where servers have different exponential service times. Furthermore, it aids understanding of kanban systems.


The Use Of Sacrificial Support Structures In A Rapid Machining Process, Wutthigrai Boonsuk, Matthew C. Frank 2019 Iowa State University

The Use Of Sacrificial Support Structures In A Rapid Machining Process, Wutthigrai Boonsuk, Matthew C. Frank

Matthew C. Frank

Rapid prototyping techniques for CNC machining have been developed in an effort to produce functional prototypes in appropriate materials. One of the major challenges is to develop an automatic fixturing system for the part during the milling process. The current proposed method, sacrificial support fixturing, is similar to the support structures used in existing rapid processes, such as Stereolithography. During the machining process, the sacrificial supports emerge incrementally and, at the end of the process, are the only entities connecting the part to the stock material. In this paper, we propose methodologies for the design of sacrificial support structures for ...


Developing And Testing Of An Upper Limb Exoskeleton For Stroke Patients, Drew Dudley, David Salazar 2019 University of Nebraska at Omaha

Developing And Testing Of An Upper Limb Exoskeleton For Stroke Patients, Drew Dudley, David Salazar

Student Research and Creative Activity Fair

Objective: The main objective of this study was to determine functional and neuromuscular outcomes of stroke patients using their non-preferred hand with and without a 3D printed passive exoskeleton compared to controls using their non-preferred hand with and without the passive exoskeleton. Methods: Adults at least six months post stroke (Stroke, n = 5) and age- and sex- matched healthy controls (Control, n = 5) performed nine trials of a gross motor task while having their brain activity measured. The Fugl-Meyer and “Box and Block” test was used to measure the gross dexterity of the subjects with and without the exoskeleton. Strength ...


Efficacy Of Assistive Devices Produced With Additive Manufacturing, James Pierce 2019 University of Nebraska at Omaha

Efficacy Of Assistive Devices Produced With Additive Manufacturing, James Pierce

Student Research and Creative Activity Fair

Despite the frequency of musculoskeletal injuries such as sprains, broken bones and torn ligaments1, treatment options are often costly, time-consuming and ill-fitted.2,3 Additive manufacturing (“3D-printing) allows for the production of highly-customized and inexpensive assistive devices4, which suggests potential efficacy in the prescription of splints and casts for musculoskeletal injury.3 In the present study, a parametric, customizable splint/cast was created using a computer-aided design (CAD) package (Fusion 360, Autodesk, San Rafael, CA, USA) and produced with low-cost, desktop 3D printing (Ultimaker 2+ Extended, Ultimaker, Geldermalsen, Netherlands). Fitting of the devices was performed on five healthy ...


Performance Analysis Of Isentropic Fluid Based Vapor Compression Refrigeration In Different Weather Conditions In Northern India, Adil Wazeer, Vishwas Nagrath, Kaushalendra Kumar Dubey, Sudipto Sarkar 2019 Galgotias University, Greater Noida

Performance Analysis Of Isentropic Fluid Based Vapor Compression Refrigeration In Different Weather Conditions In Northern India, Adil Wazeer, Vishwas Nagrath, Kaushalendra Kumar Dubey, Sudipto Sarkar

Journal of Asian Energy Studies

This study conducts an experimental analysis of a vapor compression refrigeration system (VCRS) test rig on the basis of first and second laws of thermodynamics. Performance analysis of the VCRS was conducted in winter and summer climatic conditions. The results show that high coefficient of performance (COP) is achieved in winter under both first and second law of thermodynamics analysis.


Reactive Ion Etching Selectivity Of Si/Sio2: Comparing Of Two fluorocarbon Gases Chf3 And Cf4, Meiyue Zhang, Pat Watson 2019 Singh Center for Nanotechnology

Reactive Ion Etching Selectivity Of Si/Sio2: Comparing Of Two fluorocarbon Gases Chf3 And Cf4, Meiyue Zhang, Pat Watson

Protocols and Reports

Two reactive ion etching (RIE) processes were studied to show the relative etch selectivity between SiO2 and Si using two fluorocarbon gases, CF4 and CHF3. Results show that CHF3 gives better selectivity (16:1) over CF4 (1.2 :1). On the other hand, the etch rate of SiO2 of CF4 is approximately 52.8 nm/min, faster than CHF3 (32.4 nm/min).


Interactions Between Dislocations And Three-Dimensional Annealing Twins In Face Centered Cubic Metals, Yanxiang Liang, Xiaofang Yang, Mingyu Gong, Guisen Liu, Qing Liu, Jian Wang 2019 University of Nebraska–Lincoln

Interactions Between Dislocations And Three-Dimensional Annealing Twins In Face Centered Cubic Metals, Yanxiang Liang, Xiaofang Yang, Mingyu Gong, Guisen Liu, Qing Liu, Jian Wang

Mechanical & Materials Engineering Faculty Publications

Annealing twins often form in metals with a face centered cubic structure during thermal and mechanical processing. Here, we conducted molecular dynamic (MD) simulations for copper and aluminum to study the interaction processes between {1 1 1}1/2 <1 1 0> dislocations and a three-dimensional annealing twin. Twin boundaries are characterized with Σ3{1 1 1} coherent twin boundaries (CTBs) and Σ3{1 1 2} incoherent twin boundaries (ITBs). MD results revealed that dislocation-ITB interactions affect slip transmission for a dislocation crossing CTBs, facilitating the nucleation of Lomer dislocation.


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