University of Maryland, Baltimore County
Not a member yet
17643 research outputs found
Sort by
Design of a Wing Mechanism for a Perching MAV
No full textA perching MAV utilizes a mechanism that can change its wings' position with respect to its body in order to reduce its velocity to near-zero for precision landings. This thesis examines current perching technology and applies knowledge from previous work in order to develop two conceptual mechanisms for control of the wings of a perching MAV. The first concept is designed and fabricated as a tool for learning how to apply a perching mechanism to a physical vehicle. The second concept builds on the first and attempts to make the mechanism strong enough to sustain the loads a perching MAV encounters while still being light enough for the vehicle to carry. Kinematic and physical testing are performed on both concepts. The final prototype is installed in an existing flight vehicle. It functions kinematically correct, weighs less than the payload capacity of the aircraft, and can theoretically sustain flight loads, but actuator failures inhibit its ability to fly
AERODYNAMIC & ELECTROMAGNETIC MODELING & ANALYSIS OF A VARIABLE TORQUE GENERATOR FOR WIND TURBINE APPLICATIONS
No full textThe use of a variable torque generator (VTG) with a movable stator relative to the rotor in the drivetrain of a wind turbine is investigated theoretically and computationally. This feature allows the use of a larger capacity generator in wind turbines to increase the rated power in high wind speeds and still keep them in operation in even lower than cut-in speed ranges. Thus, by harnessing more wind power throughout the entire power curve of the wind turbine, from the new cut-in speed to the cut-out speed, the efficiency of the wind turbine can be increased. The stator and the frame of the generator can be attached to a movable frame and changes in overlap can be mechanically achieved by a worm and worm gear system connected to the movable frame. Theoretical analyses together with computational methods on several wind turbine generators illustrate the advantages of having VTG feature in terms of decreasing the cut-in speed, increasing the rated power, and at the end improving the efficiency of a wind turbine. The aerodynamic and electromagnetic properties of the wind turbine are combined to make the best estimation on changing in overlap. At the end, simulation and mathematical results are presented and possible advantages of VTG with focus on on-shore wind turbine applications are discussed
Mode I and Mode II Transverse Toughness and Crack Propagation Characterization of Carbon Nano-Structure Infused High Strength Fiber Composites
No full textCarbon Nano-Structures (CNSs) infused in-situ on glass and carbon fiber filament bundles via Chemical Vapor Deposition (CVD) were implemented in attempt to improve the Mode I and Mode II transverse toughness and crack propagation resistance of corresponding unidirectional composite plies. Fractography was performed on failed specimens using optical and electron microscopy. Also, Mode I R-curves were developed to analyze the specimen's resistance to crack extension once a critical crack developed. Lastly, Digital Image Correlation was performed to determine the local displacement field near the crack tip. The glass fiber panels with CNS growth showed a reduction in Mode I transverse toughness and minimal reduction in Mode II transverse toughness compared to panels with no CNS growth. The Carbon Fiber panel showed improvements in transverse toughness for both the Mode I and Mode II loading regime of 21.8 % and 31.8 % respectively
Reliability of Structural Equation Modeling in Examining Resting State Motor Network in Healthy Subjects
No full textResting state connectivity studies are of growing significance and interest in the current neuroimaging literature due to their potential in explaining various underlying brain mechanisms and, therefore, their utility in clinical applications. While functional connectivity has been extensively examined in the human brain, effective connectivity is a burgeoning field in functional neuroimaging studies, and there is an increased interest in quantifying effective connectivity that takes into account the directional influences of various brain regions active in a particular functional network. Studies have shown the presence of multiple functional networks in the resting state, which have been shown to be consistent across subjects and between sessions. However, this is not the case with resting state effective connectivity. In this thesis we evaluate effective connectivity of the resting state motor network in normal subjects using structural equation modeling (SEM), a linear statistical analysis method. It has been shown that signals related to cardiac pulsatality and respiration effects can confound functional MRI results. Thus, we have investigated the effect of various filtering strategies on the reliability of effective connectivity measurements. In this thesis, we examined the effect of four methods of physiological filtering of resting state data: (a) preprocessed data without any filtering, (b) removal of prospectively recorded cardiac and respiratory fluctuations using RETROICOR, (c) removal of global average signal from all the brain voxels time series, (d) regressing out average signal of the white matter (WM) and cerebrospinal fluid (CSF), and (e) temporal filtering to remove frequencies pertinent to cardiac and respiratory sources. The resulting effect of each of these methods on the estimation of resting state motor network effective connectivity was examined in this thesis. We identified two plausible models for resting state effective connectivity, that were both functionally feasible and provided good fits to the datasets considered. We also examined the effects of the filtering methods on the path coefficient values of the directional connections. While in model 2 there is a significant effect of the filtering methods on the effective connectivity estimates, this is not so clear with model 1, wherein the RETROICOR filtered dataset does not significantly change the path coefficient values from the dataset with no filtering. We also show that while the physiologically filtered dataset and the global signal filtered dataset yielded the most reliable estimates of path coefficients, global filtered and WmCsf filtered dataset were the least reliable amongst the datasets considered. The results also show that the path coefficients obtained at the subject level and the session level displayed a high degree of variability. Given the variability of effective connectivity from SEM, we suggest that the results of effective connectivity be interpreted with caution
Responses and constitutive modeling of aluminum alloys, and strain-rate and temperature dependent failure criteria for F.C.C. and H.C.P. metals
No full textThe thermo-mechanical response of Al 2024-T351 under uniaxial compression loading are presented. Below certain threshold temperature, negligible strain-rate sensitivity is observed during quasi-static regime, while significant strain rate sensitivity is measured at dynamic strain-rates. Above threshold temperature, increasing strain-rate sensitivity has been observed. Based on these observations, KHL phenomenological constitutive model is significantly modified to predict the mechanical behavior of the alloy. Correlations with this modified model are shown very close to the observed responses. The second aim of this investigation is to establish a universal, accurate and robust failure criterion for ductile solids. New experimental results, along with published data on the Al 2024-T351 alloy by Stoughton and Yoon (2011), are used to establish a phenomenological failure criterion using the magnitude of stress vector and the first invariant of stress tensor. Moreover, the proposed failure criterion is used for prediction of the published results by Bruenig et al. (2008). This proposed isotropic failure criterion, based on the magnitude of stress vector (MSV), is further developed to include strain rate and temperature dependences. Based on experiment results, an exponential loading is included to simulate the strain rate effect; the KHL hardening model type temperature dependent term is also included to correlate with the observed temperature sensitivity of the failure of Al2024-T351 alloy. These modifications allow the proposed MSV failure criterion to predict the failure of Al 2024-T351 alloy over wide ranges of strain rate and temperature. Further, by demonstrating the influence of hydrostatic pressure on the anisotropic failure behavior of a HCP alloy, a new uncoupled anisotropic failure criterion is established. To comprehensively consider the anisotropy and tension compression asymmetry in the Ti-6Al-4V alloy, the modified Hill anisotropic function proposed by Khan and Yu (2011b), is used to describe the geometry of the anisotropic failure loci in principal stress space. Moreover, the KHL hardening mode type strain rate and temperature terms are adopted in the new anisotropic failure criterion to predict the failure strength of the Ti-6Al-4V alloy. Excellent correlation between predicted failure loci and the corresponding failure observations is demonstrated
STRUCTURAL EXPLORATIONS TO THE PURINE SCAFFOLD FOR USE IN NUCLEOSIDE DRUG DESIGN
No full textPurines are one of the most ubiquitous heterocyclic ring systems in nature and consequently, they are components in numerous biologically significant molecules. As a consequence they possess an excellent scaffold that may be exploited to interrogate enzyme structure and function, as well as for the development of new, potent therapeutic compounds. There are numerous examples in the literature of modifications that truly highlight the immense utility of these heterocycles. Consequently, three different, yet structurally related series of modified nucleoside(tide) analogues were sought in this work. The first project describes the synthesis of a series of thieno-expanded purine 2'-deoxy analogues that were designed to interrogate nucleic acid structure and function as well as to potentially provide the framework for novel biological agents. The second project is directly related to the expanded analogues, and focuses on a group of 2'-deoxy flexible nucleoside analogues called fleximers. This new class of unique shape-modified nucleosides introduces flexibility to the heteroaromatic purine ring by splitting it into its two components (for example, an imidazole and pyrimidine ring). This imparts additional degrees of conformational freedom and torsional flexibility while still retaining the molecular elements necessary for recognition. These innovative nucleosides are an extension of two series of ribose fleximers previously introduced by the Seley-Radtke laboratories. It is hoped that this new series of fleximers will expand the repertoire of active compounds especially after observing the exciting biological results observed by the ribose series. The third project highlights the use of thieno-expanded purine ribose derivatives, in the nucleoside as well as the triphosphate forms, as potential inhibitors of HCV. Motivation for this project was especially warranted following reports in the literature that inclusion of a pendant thiophene ring significantly increased inhibition against HCV for some inhibitors. All of the compounds that were pursued for this research have provided valuable information about nucleoside structure and function, as well as enzyme-ligand interactions, thereby providing a solid foundation for further study
Anisotropic Responses of a Ti-6Al-4V alloy, and development of a strain rate and temperature dependent yield criterion and constitutive model for HCP alloys
No full textThe deformation induced anisotropic mechanical responses of an electron beam single melt Ti-6Al-4V alloy are characterized over wide ranges of strain rates, temperatures and hydrostatic pressures, along different directions. Based on the experimental observation, the KHL model is used to predict the observed mechanical behaviors. Close agreement is found between the predicted results and the experimental observations. Based on the experimental results, a yield criterion is proposed to describe the anisotropy and tension compression asymmetry characteristics of this alloy. In the proposed anisotropic yield criterion, a novel method is introduced to decouple the anisotropy and tension compression asymmetry characteristics; the anisotropic coefficients and tension compression asymmetry parameter can be determined independently. The KHL model is used as the hardening response, and subsequently used to determine the material constants in the proposed yield criterion. Moreover, the newly proposed yield criterion is used to correlate the yield loci of the Ti-6Al-4V alloy at different strain levels, strain rates and temperatures. Excellent agreement between predicted yield surfaces and corresponding experimental data is obtained A generalized anisotropic associative constitutive model is established for anisotropic metals with tension-compression asymmetry. The stress strain hardening behavior of the Ti-6Al-4V alloy, based on KHL constitutive model, is adopted to include the influences of strain rate and temperature on the plastic deformation of the material. The newly proposed yield criterion is introduced to predict the initial yield and subsequent working-hardening surfaces of the Ti alloy under loading conditions. Based on the associative flow rule, the KHL hardening model and the newly proposed yield criterion are combined into the anisotropic, strain rate and temperature dependent associative constitutive model. A user defined material subroutine (UMAT) for ABAQUS, is programmed based on the backward Euler's stress integration and radial return mapping techniques. By establishing the finite element models and implementing the UMAT in ABAQUS, the mechanical responses of the Ti alloy under uniaxial loadings are simulated. Moreover, the validity of the proposed associative constitutive model and the UMAT is further verified by comparing the simulation and experimental results on the mechanical response of the alloy under multiaxial loading conditions
Minutes of the 52nd meeting of the Council of the International Union of Immunological Societies
No full textMeeting minutes for the 52nd meeting of the Council of the IUIS, held on August 19th, 2007 in Rio de Janeiro, Brazi
[EB 2011, Henry Gray Scientific Achievement Award recipient]
No full text[Title supplied by cataloger]AAA Awards Banquet at the 2011 Experimental Biology conference. L-R Outgoing President Kathy Jones, Henry Gray Scientific Achievement Award Recipient Bjorn Olsen & Past President David Burr