Mechanical Engineering Commons^™

Comparison Of 4d Phase-Contrast Mri Flow Measurements To Computational Fluid Dynamics Simulations Of Cerebrospinal Fluid Motion In The Cervical Spine, Theresia Yiallourou, Jan Robert Kroger, Nikolaos Stergiopulos, David Maintz, Bryn A. Martin, Alexander C. Bunck

Mechanical Engineering Faculty Research

Cerebrospinal fluid (CSF) dynamics in the cervical spinal subarachnoid space (SSS) have been thought to be important to help diagnose and assess craniospinal disorders such as Chiari I malformation (CM). In this study we obtained time-resolved three directional velocity encoded phase-contrast MRI (4D PC MRI) in three healthy volunteers and four CM patients and compared the 4D PC MRI measurements to subject-specific 3D computational fluid dynamics (CFD) simulations. The CFD simulations considered the geometry to be rigid-walled and did not include small anatomical structures such as nerve roots, denticulate ligaments and arachnoid trabeculae. Results were compared at nine axial planes …

Inertia Gap Between Md Simulations And Afm Experiments In Study Of Atomic Friction, Yalin Dong, Qunyang Li, Robert W. Carpick, Ashlie Martini

Mechanical Engineering Faculty Research

Both atomic force microscopy (AFM) experiments and molecular dynamics (MD) simulation are carried out to investigate atomic stick-slip friction by sliding a Pt tip on an Au substrate. Efforts are taken to match the conditions for AFM experiment and MD simulation as closely as possible. The results show that AFM and MD provide consistent energetic parameters, which suggests that MD simulations can be reliably used to interpret energetic aspects of the interfaces. However, orders of magnitude differences in attempt frequencies are found, which indicates another challenge between the MD simulations and AFM experiments, i.e., the inertia gap.

A Nano-Cheese-Cutter To Directly Measure Interfacial Adhesion Of Freestanding Nano-Fibers, Xin Wang, Johnny F. Najem, Shing Chung Josh Wong, Kai-Tak Wan

Mechanical Engineering Faculty Research

A nano-cheese-cutter is fabricated to directly measure the adhesion between two freestanding nano-fibers. A single electrospun fiber is attached to the free end of an atomic force microscope cantilever, while a similar fiber is similarly prepared on a mica substrate in an orthogonal direction. External load is applied to deform the two fibers into complementary V-shapes, and the force measurement allows the elastic modulus to be determined. At a critical tensile load, “pull-off” occurs when the adhering fibers spontaneously detach from each other, yielding the interfacial adhesion energy. Loading-unloading cycles are performed to investigate repeated adhesion-detachment and surface degradation.

Sheathless Size-Based Acoustic Particle Separation, Rasim Guldiken, Myeong Chan Jo, Nathan D. Gallant, Utkan Demirci, Jiang Zhe

Mechanical Engineering Faculty Research

Particle separation is of great interest in many biological and biomedical applications. Flow-based methods have been used to sort particles and cells. However, the main challenge with flow based particle separation systems is the need for a sheath flow for successful operation. Existence of the sheath liquid dilutes the analyte, necessitates precise flow control between sample and sheath flow, requires a complicated design to create sheath flow and separation efficiency depends on the sheath liquid composition. In this paper, we present a microfluidic platform for sheathless particle separation using standing surface acoustic waves. In this platform, particles are first lined …

Process Completing Sequences For Resource Allocation Systems With Synchronization, Song Foh Chew, Shengyong Wang

Mechanical Engineering Faculty Research

This paper considers the problem of establishing live resource allocation in workflows with synchronization stages. Establishing live resource allocation in this class of systems is challenging since deciding whether a given level of resource capacities is sufficient to complete a single process is NP-complete. In this paper, we develop two necessary conditions and one sufficient condition that provide quickly computable tests for the existence of process completing sequences. The necessary conditions are based on the sequence of completions of � subprocesses that merge together at a synchronization. Although the worst case complexity is O(2�), we expect the number of subprocesses …

Negative Effective Mass Density Of Acoustic Metamaterial Using Dual-Resonator Spring-Mass Model, Kwek Tze Tan, H. H. Huang, C. T. Sun

Mechanical Engineering Faculty Research

In this paper, we propose an acoustic metamaterial with a microstructure consisting of two internal resonators. The performance of this dual-resonator metamaterial is compared to the original singleresonator metamaterial. Analytical findings show that the dual-resonator metamaterial exhibits its negative effective mass density over a larger frequency spectrum, particularly at two distinctively asymptotic regions. The wave propagation phenomenon in the metamaterial is investigated using finite element simulation. Computational results reveal that the dual-resonator metamaterial is capable of attenuating wave propagation in a larger operating frequency. Practical applications like vibration control and blast mitigation are demonstrated and discussed.

Validation Of Delamination Reduction Trend For Stitched Composites Using Quasi-Static Indentation Test, Kwek Tze Tan, N. Watanabe, A. Yoshimura, Y. Iwahori

Mechanical Engineering Faculty Research

A novel empirical-based Delamination Reduction Trend (DRT) for stitched composites has been recently proposed. The DRT is capable of predicting the effective reduction in impact induced delamination area due to the influence of stitching. DRT simply relates two parameters: normalized delamination area and stitch fibre volume fraction, to characterize the effectiveness of stitching in impact damage suppression. This paper seeks to validate the DRT by using quasi-static indentation (QSI) test, which is considered analogous to low velocity impact test, due to similar structural response. Results from QSI test show good agreement with DRT. Furthermore, limitations in DRT have been established.

Design Charts For Circular Fins Of Arbitrary Profile Subject To Radiation And Convection With Wall Resistances, G. Zhang, Benjamin T.F. Chung

Mechanical Engineering Faculty Research

In this work, the optimization for a radiative-convective annular fin of arbitrary profile with base wall thermal resistances is considered. A fourth order Runge-Kutta method is used to solve the associated non-linear governing equa-tions. Further differentiations yield the optimum heat transfer and the optimum fin dimensions. To facilitate the thermal design, design charts for optimum dimensions are proposed. Furthermore, the fin effectiveness for the optimal annular ra-diative-convective fins is presented to check the practicality of the design.

http://dx.doi.org/10.2174/1874396X01206010015