Vibrational Power Flow Analysis of Rods and Beams

A new method to model vibrational power flow and predict the resulting energy density levels in uniform rods and beams is investigated. This method models the flow of vibrational power in a manner analogous to the flow of thermal power in a heat conduction problem. The classical displacement solutions for harmonically excited, hysteretically damped rods and beams are used to derive expressions for the vibrational power flow and energy density in the rod and beam. Under certain conditions, the power flow in these two structural elements will be shown to be proportional to the energy density gradient. Using the relationship between power flow and energy density, an energy balance on differential control volumes in the rod and beam leads to a Poisson's equation which models the energy density distribution in the rod and beam. Coupling the energy density and power flow solutions for rods and beams is also discussed. It is shown that the resonant behavior of finite structures complicates the coupling of solutions, especially when the excitations are single frequency inputs. Two coupling formulations are discussed, the first based on the receptance method, and the second on the travelling wave approach used in Statistical Energy Analysis. The receptance method is the more computationally intensive but is capable of analyzing single frequency excitation cases. The traveling wave approach gives a good approximation of the frequency average of energy density and power flow in coupled systems, and thus, is an efficient technique for use with broadband frequency excitation

The role of the N domain in substrate binding, oligomerization, and allosteric regulation of the AAA+ Lon protease

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biology, June 2013."June 2013." Cataloged from PDF version of thesis.Includes bibliographical references.For cells and organisms to survive, they must maintain protein homeostasis in varied and often harsh environments. Cells utilize proteases and chaperones to maintain their proteomes. In bacteria, most cytosolic proteolysis is performed by self-compartmentalized AAA+ proteases, which convert the chemical energy of ATP binding and hydrolysis into mechanical work to unfold and translocate substrates into an internal degradation chamber. Substrates are targeted to AAA+ proteases by degradation tags (degrons). In E. coli, the Lon protease is responsible for the degradation of numerous regulatory proteins, including the cell-division inhibitor SulA, but also recognizes and degrades the majority of misfolded proteins. How Lon recognizes and prioritizes such a vast array of substrates is poorly understood. Active Lon is a homohexamer in which each subunit contains an N domain, a AAA+ module that mediates ATP binding and hydrolysis, and a peptidase domain. Degron binding allosterically regulates Lon activity and can shift Lon into conformations with higher or lower protease activity, but the mechanistic basis of this regulation is unknown. The low-protease conformation of Lon may serve as a chaperone. In Chapter 2, I describe the development and characterization of fluorescent model substrates that Lon degrades in vitro and in vivo. In Chapter 3, I describe collaborative experiments that show that Lon equilibrates between a hexamer and a dodecamer. Based on biochemical analysis and a low-resolution EM dodecamer structure, Lon appears to shift its substrate profile by changing oligomeric states and contacts between N domains appear to stabilize the dodecamer. In Chapters 4 and 5, 1 identify a binding site for the sul20 degron (isolated from SulA) in the Lon N domain and demonstrate that substrate binding to this site allosterically regulates protease and ATPase activity. I also show that the E240K mutation in the N domain alters Lon activity and stabilizes dodecamers. Finally, I provide evidence that E. coli Lon can act as a chaperone in vivo. These experiments demonstrate that the N domain integrates substrate binding, oligomerization, and regulation of the catalytic activities of Lon.by Matthew L. Wohlever.Ph.D

Sound transmission through the walls of light aircraft: An investigation of structure-borne noise in a Handley Page 137 Jetstream 3 aircraft

This study indicates that the structureborne noise due to wing/vortex interation for the Handley Page-137 Jetstream may be significant at frequencies above 500 Hz. It was found that by preventing such interaction, noise reductions between 1 to 3 dB were attainable. However, this study did not show any significant contribution due to this phenomena at the first blade passage tone. It is suspected that the wing/vortex interaction effect varies from plane to plane

Roles of the N domain of the AAA+ Lon protease in substrate recognition, allosteric regulation and chaperone activity

Degron binding regulates the activities of the AAA+ Lon protease in addition to targeting proteins for degradation. The sul20 degron from the cell-division inhibitor SulA is shown here to bind to the N domain of Escherichia coli Lon, and the recognition site is identified by cross-linking and scanning for mutations that prevent sul20-peptide binding. These N-domain mutations limit the rates of proteolysis of model sul20-tagged substrates and ATP hydrolysis by an allosteric mechanism. Lon inactivation of SulA in vivo requires binding to the N domain and robust ATP hydrolysis but does not require degradation or translocation into the proteolytic chamber. Lon-mediated relief of proteotoxic stress and protein aggregation in vivo can also occur without degradation but is not dependent on robust ATP hydrolysis. In combination, these results demonstrate that Lon can function as a protease or a chaperone and reveal that some of its ATP-dependent biological activities do not require translocation.National Institutes of Health (U.S.) (Grant AI-16982)National Science Foundation (U.S.). Graduate Research Fellowship Progra

Altering the electron transfer mechanism of cytochrome P450 reductase through a single point mutation

Cytochrome P450 reductase (CPR) is an electron transporter enzyme that plays an essential role in xenobiotic transformations, including metabolism of carcinogens, environmental agents, and drugs. CPR, a membrane bound flavoprotein, contains two flavin cofactors--flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN)--each bound to a separate protein domain. Both flavin cofactors utilize three distinct oxidation states: oxidized (OX), semiquinone (SQ) (one electron reduced), and hydroquinone (HQ) (two electron reduced). The multiple oxidation states of the flavin cofactors allow CPR to catalyze the essential transfer of electrons from the obligate two-electron donor NADPH to the one-electron acceptor heme-iron of cytochrome P450. A comparison of the FMN-binding domains in various related flavoproteins reveals that the FMN binding loops differ in their size, conformations, and primary structure yet each contains a conserved glycine residue. My research project was designed to evaluate the functional significance of this conserved glycine in rat CPR (Gly-141) through its replacement with threonine using site-directed mutagenesis. This replacement was made in both the intact reductase and the isolated FMN-binding domain (FBD). Based on previous research on the flavodoxin, we hypothesized that the larger, beta-branched side chain of threonine would disrupt the hydrogen bond between residue 141’s carbonyl group and the N5H of the reduced flavin, which should destabilize the functionally relevant semiquinone state. Using a standard steady-state turnover activity assay for cytochrome reduction and the physiological reductant NADPH, the G141T mutant was found to exhibit a specific activity that is 30% less than that of the wild type reductase, indicating that the conserved glycine residue helps modulate electron transfer. A distinctive characteristic of CPR is that the thermodynamically stable neutral FMN SQ serves as the primary electron donor to cytochrome P450. This phenomenon is the direct result of the substantial separation of the midpoint potentials for the OX/SQ and SQ/HQ redox couples (-43 mV and -280 mV, respectively). Reductive titrations of the G141T mutant revealed a significantly lower formation of the FMN SQ at thermodynamic equilibrium in both CPR and the FBD. The direct measurement of the midpoint potentials for this mutant indicated values for the OX/SQ and SQ/HQ couples of -250 mV and -218 mV, respectively. Thus, the midpoint potential for the OX/SQ couple has decreased substantially resulting in a significant loss in stability of the SQ state with the HQ state becoming the most stable thermodynamically. When wild-type CPR is mixed with an equimolar concentration of NADPH in a stopped-flow spectrophotometer, the disemiquinoid species is formed. However, when the experiment is repeated with G141T CPR, the FAD OX, FMN HQ species are preferentially formed. This data suggests that G141T CPR utilizes the FMN HQ as the primary electron donor to the cytochrome rather than the FMN SQ, but apparently in a less efficient manner. Thus the conserved glycine residue plays a critical role in stabilizing the reduced forms of the FMN cofactor, and in determining the mechanism of electron transfer in CPR. Advisor: Dr. Richard P. SwensonA one-year embargo was granted for this item

Benchmarking real-time distributed object management systems for evolvable and adaptable command and control applications

Abstract This paper describes benchmarking for evolvable and adaptable real-time command and control systems Introduction MITRE's Evolvable Real-Time C3 initiative developed an approach that would enable current real-time systems to evolve into the systems of the future. We designed and implemented an infrastructure and data manager so that various applications could be hosted on the infrastructure. Then we completed a follow-on effort to design flexible adaptable distributed object management systems for command and control (C2) systems. Such an adaptable system would switch scheduling algorithms, policies, and protocols depending on the need and the environment. Both initiatives were carried out for the United States Air Force. One of the key contributions of our work is the investigation of real-time features for distributed object management systems. Partly as a result of our work we are now seeing various real-time distributed object management products being developed. In selecting a real-time distributed object management systems, we need to analyze various criteria. Therefore, we need benchmarking studies for realtime distributed object management systems. Although benchmarking systems such as Hartstone and Distributed Hartstone have been developed for middleware systems, these systems are not developed specifically for distributed object-based middleware. Since much of our work is heavily based on distributed objects, we developed benchmarking systems by adapting the Hartstone system. This paper describes out effort on developing benchmarks. In section 2 we discuss Distributed Hartstone. Then in section 3, we first provide background on the original Hartstone and DHartstone designs from SEI (Software Engineering Institute) and CMU (Carnegie Mellon University). We then describe our design and modification of DHartstone to incorporate the capability to benchmark real-time middleware in Section 4. Sections 5 and 6 describe the design of the benchmarking systems. For more details of our work on benchmarking and experimental results we refer to [MAUR98] and [MAUR99]. For background information of our work we refer t

Symmetry, Nonlinear Bifurcation Analysis, and Parallel Computation

In the natural and engineering sciences the equations which model physical systems with symmetry often exhibit an invariance with respect to a particular group G of linear transformations. G is typically a linear representation of a symmetry group G which characterizes the symmetry of the physical system. In this work, we will discuss the natural parallelism which arises while seeking families of solutions to a specific class of nonlinear vector equations which display a special type of group invariance, referred to as equivariance. The inherent parallelism stems from a global de-coupling, due to symmetry, of the full nonlinear equations which effectively splits the original problem into a set of smaller problems. Numerical results from a symmetry-adapted numerical procedure, (MMcontcm.m), written in MultiMATLAB 1 are discussed. 1 Introduction Consider the task of finding solutions to the following vector equilibrium equation f (u; ) = 0; f : R n \Theta R 7! R n : (1) In eq: ..

A preliminary evaluation of the B2000 nonlinear shell element Q8N.SM

Aerospace Engineerin

A preliminary evaluation of the B2000 nonlinear shell element Q8N.SM

Over the past ten years, there has been a growing interest within the mechanics community towards the application of group theoretic methods to aid in the global buckling analysis of symmetric-free structures. Within the context of a numerical arclength continuation procedure, group theory helps one systematically find an "optimal" set of basic vectors which reflect the symmetry of a given problem. The immediate payoff in formulating the numerical procedure with respect to the symmetry-adapted basis is a global de-coupling of the equilibrium equations which in turn leads to: (1) a dimensional reduction in the problem size; (2) improved numerical conditioning while computing solutions in the vicinity of singular points; (3) a systematic method for detecting and diagnosing for symmetry-breaking bifurcations. In this book, a new group theoretic nonlinear continuation algorithm, written for the modular finite element package B2000, will be discussed. The focus of the work was to provide a general computational environment in which a wide range of symmetric problems for structural mechanics could be formulated and solved. A group theoretic approach allows the computation of equilibrium solutions for perfect structures which might otherwise be numerically intracebie. Furthermore, understanding the global behaviour of the perfect structure can be crucial to understanding the behavior of the imperfect structure. Numerical examples to be presented include results from the buckling analysis of a flat plate and an axially compressed cylindrical shell.Aerospace Engineerin