GA Institute of Technology

Atlanta, GA, United States

GA Institute of Technology

Atlanta, GA, United States
SEARCH FILTERS
Time filter
Source Type

Rachev A.,GA Institute of Technology | Felden L.,GA Institute of Technology | Ku D.N.,GA Institute of Technology
Journal of Biomechanical Engineering | Year: 2011

The study provides a pathway to design a mechanics-matching vascular graft for an end-to-end anastomosis to a host artery. For functional equivalence, we submit that the graft and a host artery should have equal inner deformed diameters, equal pressure-radius module, and experience equal axial forces when subjected to mean arterial pressure. These criteria for mechanical equivalence are valid for a large class of materials that can be considered as elastic incompressible and orthotropic solids. As an example, specific known artery properties were used to design or select a graft made from a new synthetic biomaterial to demonstrate that reliable and robust technology for graft fabrication is possible. © 2011 American Society of Mechanical Engineers.


Jiang Y.,South China University of Technology | Jiang Z.-J.,South China University of Technology | Chen B.,South China University of Technology | Jiang Z.,Ningbo University of Technology | And 5 more authors.
Journal of Materials Chemistry A | Year: 2016

MnO2 nanorods grown on reduced graphene oxide (MnO2-NR/rGO) have been synthesized through a hydrothermal treatment of the reaction product between KMnO4 and 2-(N-morpholino)ethanesulfonic acid in the presence of graphene oxide. When tested as an anode in a lithium-ion battery (LIB), the obtained MnO2-NR/rGO exhibits a significant enhancement in electrochemical performance, especially after being discharged/charged for 300 cycles. Characterization of the microscopic features suggests that the morphology and crystal structure of the MnO2 nanorods evolve gradually during cycling, transforming the product of the MnO2-NR/rGO into a unique electrode architecture consisting of well-separated rGO coated with well-crystallized λ-MnO2 after 300 cycles. The significantly enhanced electrochemical performance of the MnO2-NR/rGO electrode after 300 cycles is attributed mainly to the resulting electrode architecture, which enhances the interaction between MnO2 and rGO, reduces the charge transfer resistance across the MnO2/rGO interface, and makes the rGO readily accessible to lithium ion storage. The demonstrated specific capacity and rate capability are among the best ever reported for transition metal oxide based electrodes for LIBs. © The Royal Society of Chemistry 2016.


Zheng D.,Chengdu University of Technology | Frost J.D.,GA Institute of Technology | Huang R.Q.,Chengdu University of Technology | Liu F.Z.,GA Institute of Technology
Engineering Geology | Year: 2015

The analysis of the failure processes and mechanisms of rockfalls that are associated with underground mining activities is presented. The study area is located in Kaiyang Phosphorite Mine in Southwest China, where the geological condition is dominated by anti-dip slopes with layers inclined backward into the natural slope with decreasing strength in the rock mass from the upper (dolomite-rich) to the lower (shale-rich) strata. The analysis is based on field investigation and laboratory experimental study using a gravitational simulation device. The results support the proposed failure mechanism by demonstrating the process of failure from the deformation of the roof and floor in the stopes, to the development of surface cracks near the top of slopes, and eventually to the formation of rockfalls as the surface cracks propagate along pre-existing joints. The rockfalls are classified into one of three failure modes: crack-toppling, crack-sliding, and crack-slumping, in which the failures are governed by the corresponding characteristics of the rock mass structure. The study of the failure process and their spatial and temporal correlation with the underground workings reveals warning signs or indicators of impending slope instability. Improved understanding of the failure process and indicators can aid in early identification and timely warning of geohazards in phosphorite mines. © 2015 Elsevier B.V.


Jiang Y.,South China University of Technology | Jiang Z.-J.,South China University of Technology | Cheng S.,South China University of Technology | Liu M.,South China University of Technology | Liu M.,GA Institute of Technology
Electrochimica Acta | Year: 2014

A 3-dimensional porous graphene material (PGM) has been synthesized using a simple two-step process: hydrothermal reaction and calcination. Hydrothermal reaction of graphene oxide (GO) in the presence of resorcinol and glutaraldehyde leads to covalent grafting of partially reduced GO with glutaraldehyde and the deposition of phenolic resin. Subsequent calcination of the composite consisting of phenolic resin deposited on partially reduced GO in the presence of KOH produces structurally stable, highly porous graphene material with a specific surface area of ∼1,066 ± 2 m2 g-1. When used as an active electrode material in a lithium battery, the PGM exhibits an initial discharge capacity of ∼1,538 mAh g-1, which is significantly higher than those of graphite and other carbonaceous materials reported previously. More importantly, when cycled at higher discharge/charge rates, the PGM-based electrodes still deliver large capacities and excellent cycling performance, demonstrating great potential for high-performance lithium-ion batteries. The attractive electrochemical performance of the PGM is attributed to its unique porous structure with large specific surface area and the presence of more disordered carbon atoms produced by the KOH activation. © 2014 Elsevier Ltd. All rights reserved.


Narisetti R.K.,GA Institute of Technology | Ruzzene M.,GA Institute of Technology | Leamy M.J.,GA Institute of Technology
Journal of Vibration and Acoustics, Transactions of the ASME | Year: 2011

The paper investigates wave dispersion in two-dimensional, weakly nonlinear periodic lattices. A perturbation approach, originally developed for one-dimensional systems and extended herein, allows for closed-form determination of the effects nonlinearities have on dispersion and group velocity. These expressions are used to identify amplitude-dependent bandgaps, and wave directivity in the anisotropic setting. The predictions from the perturbation technique are verified by numerically integrating the lattice equations of motion. For small amplitude waves, excellent agreement is documented for dispersion relationships and directivity patterns. Further, numerical simulations demonstrate that the response in anisotropic nonlinear lattices is characterized by amplitude-dependent "dead zones." © 2011 American Society of Mechanical Engineers.


Liu Y.,GA Institute of Technology | Dhingra M.,GA Institute of Technology | Prasad J.V.R.,GA Institute of Technology
Journal of Engineering for Gas Turbines and Power | Year: 2012

This paper presents a method for estimating compressor stall margin and the results of applying the estimation technique to an axial compressor rig. Stall margin estimation is accomplished through the use of a compressor stability detection parameter called the correlation measure. The correlation measure captures the periodicity of the pressure in the rotor tip region of the compressor. The downcrossing frequency of the correlation measure across some preset threshold is measured while operating the compressor rig at various steady-state points along the design speed characteristic line. These measurements are used to generate a relationship with stall margin as a function of downcrossing frequency. The estimation technique is evaluated by applying it while dynamically ramping the operating point of the compressor up the design speed line towards surge. A brief investigation on the effects of inlet distortions on the correlation measure-based estimation system is also given. © 2012 American Society of Mechanical Engineers.


Zvanut M.E.,University of Alabama at Birmingham | Uprety Y.,University of Alabama at Birmingham | Dashdorj J.,University of Alabama at Birmingham | Moseley M.,GA Institute of Technology | Alan Doolittle W.,GA Institute of Technology
Journal of Applied Physics | Year: 2011

Electron paramagnetic resonance measurements are used to monitor the passivation and activation of the Mg-related acceptor in GaN doped with different concentrations of Mg, up to 2 × 1020 cm-3. Samples were annealed in either forming gas (H2:N2) or pure N2 between 200 and 900°C. As expected, the Mg-related EPR signal is reduced by at least a factor of ten during the forming gas treatment; while the pure N2 environment revives the signal. However, the study also shows that reactions between Mg and hydrogen occur at a temperature as low as 525°C in the 1020 cm-3 Mg doped samples; while in more lightly doped samples, temperatures greater than 700°C are required to observe changes in the Mg signal intensity. While the observations support the model in which a hydrogen atom ionizes at the Mg impurity and the remaining proton bonds at a near neighbor, the different temperature dependence suggests that hydrogen diffusion is affected by the increased Mg concentration. © 2011 American Institute of Physics.


Jiang Y.,South China University of Technology | Jiang Z.-J.,South China University of Technology | Yang L.,South China University of Technology | Cheng S.,South China University of Technology | And 2 more authors.
Journal of Materials Chemistry A | Year: 2015

The encapsulation of transition metal oxide (TMO) particles in a graphene hollow shell to form a core-void-shell structure is an attractive way to improve the electrochemical performance of TMO-based electrodes for lithium ion batteries (LIBs). First, the continuous graphene shell may enhance the electrical conductivity of the electrodes and thus facilitate current collection and charge transfer associated with lithium storage. Second, the unique shell structure may suppress the aggregation of the core TMO particles while the void space between the core and shell may accommodate the large volume changes of the core during charge-discharge cycling, which enhances electrode stability against cycling. Third, the high specific surface area may improve the accessibility of active electrode materials to the electrolyte, which could effectively reduce the solid-state diffusion length and thus enhance Li ion transport and rate capability. When tested in a LIB, a Fe3O4@rGO composite electrode exhibits an initial reversible capacity of 1236.6 mA h g-1, which is much higher than that of an electrode based on bare Fe3O4, a physical mixture of Fe3O4 and graphene, or other forms of Fe3O4 reported in the literature. In addition, the cycling performance and rate capacity are also much better. The results clearly demonstrate that this unique electrode architecture is ideally suited for LIBs and other electrochemical energy storage and conversion devices. © The Royal Society of Chemistry 2015.


Senesi M.,Georgia Institute of Technology | Ruzzene M.,Georgia Institute of Technology | Ruzzene M.,GA Institute of Technology
Journal of the Acoustical Society of America | Year: 2011

A frequency selective acoustic transducer (FSAT) is proposed for directional sensing of guided waves. The considered FSAT design is characterized by a spiral configuration in wavenumber domain, which leads to a spatial arrangement of the sensing material producing output signals whose dominant frequency component is uniquely associated with the direction of incoming waves. The resulting spiral FSAT can be employed both for directional sensing and generation of guided waves, without relying on phasing and control of a large number of channels. The analytical expression of the shape of the spiral FSAT is obtained through the theoretical formulation for continuously distributed active material as part of a shaped piezoelectric device. Testing is performed by forming a discrete array through the points of the measurement grid of a scanning laser Doppler vibrometer. The discrete array approximates the continuous spiral FSAT geometry, and provides the flexibility to test several configurations. The experimental results demonstrate the strong frequency dependent directionality of the spiral FSAT and suggest its application for frequency selective acoustic sensors, to be employed for the localization of broadband acoustic events, or for the directional generation of Lamb waves for active interrogation of structural health. © 2011 Acoustical Society of America.


PubMed | GA Institute of Technology
Type: Journal Article | Journal: Journal of biomechanical engineering | Year: 2011

The study provides a pathway to design a mechanics-matching vascular graft for an end-to-end anastomosis to a host artery. For functional equivalence, we submit that the graft and a host artery should have equal inner deformed diameters, equal pressure-radius module, and experience equal axial forces when subjected to mean arterial pressure. These criteria for mechanical equivalence are valid for a large class of materials that can be considered as elastic incompressible and orthotropic solids. As an example, specific known artery properties were used to design or select a graft made from a new synthetic biomaterial to demonstrate that reliable and robust technology for graft fabrication is possible.

Loading GA Institute of Technology collaborators
Loading GA Institute of Technology collaborators