Publications

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The summary of this report is: (1) Optimizing synthesis parameters leads to enhanced catalyst surface areas - Nonlinear relationship between activity and surface area; (2) Catalyst development performed under a staged protocol; (3) Catalytic materials with desired properties have been identified - Meet stage requirements, Performance can be tuned by altering component concentrations, Optimization still necessary at low temperatures; (4) Better activity and tolerance to SO2 - V2O5-based materials ruled out because of durability issues; and (5) Future work will focus on improving overall low temperature activity.

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By means of coupled-cluster theory, molecular properties can be computed with an accuracy often exceeding that of experiment. The high-degree polynomial scaling of the coupled-cluster method, however, remains a major obstacle in the accurate theoretical treatment of mainstream chemical problems, despite tremendous progress in computer architectures. Although it has long been recognized that this super-linear scaling is non-physical, the development of efficient reduced-scaling algorithms for massively parallel computers has not been realized. We here present a locally correlated, reduced-scaling, massively parallel coupled-cluster algorithm. A sparse data representation for handling distributed, sparse multidimensional arrays has been implemented along with a set of generalized contraction routines capable of handling such arrays. The parallel implementation entails a coarse-grained parallelization, reducing interprocessor communication and distributing the largest data arrays but replicating as many arrays as possible without introducing memory bottlenecks. The performance of the algorithm is illustrated by several series of runs for glycine chains using a Linux cluster with an InfiniBand interconnect.

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The generalized momentum balance (GMB) methods, explored chiefly by Shabana and his co-workers, treat slap or collision in linear structures as sequences of impulses, thereby maintaining the linearity of the structures throughout. Further, such linear analysis is facilitated by modal representation of the structures. These methods are discussed here and extended. Simulations on a simple two-rod problem demonstrate how this modal impulse approximation affects the system both directly after each impulse as well as over the entire collision. Furthermore, these simulations illustrate how the GMB results differ from the exact solution and how mitigation of these artifacts is achieved. Another modal method discussed in this paper is the idea of imposing piecewise constant forces over short, yet finite, time intervals during contact. The derivation of this method is substantially different than that of the GMB method, yet the numerical results show similar behavior, adding credence to both models. Finally, a novel method combining these two approaches is introduced. The new method produces physically reasonable results that are numerically very close to the exact solution of the collision of two rods. This approach avoids most of the non physical, numerical artifacts of interpenetration or chatter present in the first two methods.

The purpose of modal testing is usually to provide an estimate of a linear structural dynamics model. Typical uses of the experimental modal model are (1) to compare it with a finite element model for model validation or updating; (2) to verify a plant model for a control system; or (3) to develop an experimentally based model to understand structural dynamic responses. Since these are some common end uses, for this article the main goal is to focus on excitation methods to obtain an adequate estimate of a linear structural dynamics model. The purpose of the modal test should also provide the requirements that will drive the rigor of the testing, analysis, and the amount of instrumentation. Sometimes, only the natural frequencies are required. The next level is to obtain relative mode shapes with the frequencies to correlate with a finite element model. More rigor is required to get accurate critical damping ratios if energy dissipation is important. At the highest level, a full experimental model may require the natural frequencies, damping, modal mass, scaled shapes, and, perhaps, other terms to account for out-of-band modes. There is usually a requirement on the uncertainty of the modal parameters, whether it is specifically called out or underlying. These requirements drive the meaning of the word 'adequate' in the phrase 'adequate linear estimate' for the structural dynamics model. The most popular tools for exciting structures in modal tests are shakers and impact hammers. The emphasis here will be on shakers. There have been many papers over the years that mention some of the advantages and issues associated with shaker testing. One study that is focused on getting good data with shakers is that of Peterson. Although impact hammers may seem very convenient, in many cases, shakers offer advantages in obtaining a linear model. The best choice of excitation device is somewhat dependent on the test article and logistical considerations. These considerations will be addressed in this article to help the test team make a choice between impact hammer and various shaker options. After the choice is made, there are still challenges to obtaining data for an adequate linear estimate of the desired structural dynamics model. The structural dynamics model may be a modal model with the desired quantities of natural frequencies, viscous damping ratios, and mode shapes with modal masses, or it may be the frequency response functions (FRFs), or their transforms, which may be constructed from the modal model. In any case, the fidelity of the linear model depends to a large extent on the validity of the experimental data, which are generally gathered in the form of FRFs. With the goal of obtaining an 'adequate linear estimate' for a model of the structural dynamic system under test, consider several common challenges that must be overcome in the excitation setup to gather adequate data.

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A laser hazard analysis and safety assessment was performed for each various laser diode candidates associated with the High Resolution Pulse Scanner based on the ANSI Standard Z136.1-2000, American National Standard for the Safe Use of Lasers. A theoretical laser hazard analysis model for this system was derived and an Excel{reg_sign} spreadsheet model was developed to answer the 'what if questions' associated with the various modes of operations for the various candidate diode lasers.

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