Determining the homotopy type of one-dimensional Peano continua has been an open question of some interest. We give a complete invariant of the homotopy type of such continua, which consists of a pair of subspaces together with a relative homology group. Along the way, we describe reduced forms for one-dimensional Peano continua.

Purpose: Post-COVID-19 workforce issues have pushed terms like resilience and burnout further into the forefront of professional discourse. Strategies aimed to improve resilience, decrease burnout, and increase retention appear to be less effective in the current climate. One potential unexplored contributor is toxic positivity. The purpose of this research is to analyze the concept of toxic positivity and its relevance to nursing. Aims: Research questions; “1) How is toxic positivity used across contexts?; 2) Whose perspectives are represented and whose are not?; 3) What are the dimensions of toxic positivity?; 4) How are the dimensions related?; and 5) How is toxic positivity constructed and used in nursing? Methods: Using Schatzman’s dimensional analysis approach, the first analytic phase, Identification, elucidates relevant conceptual dimensions. The second analytic phase, Logistics, examines relationships among dimensions and contexts. Finally, a dimensional matrix provides conceptualization of toxic positivity for nursing. Results: Preliminary results reveal roots of toxic positivity in the realm of positive psychology with relevant dimensions including unrealistic optimism, inauthentic platitudes, and emotional invalidation and identified contexts including business, psychology, and medicine with no identified contexts in nursing. Primary limitations include limited time to complete this analysis, lack of empirical evidence regarding toxic positivity, and the potential for other unrealized dimensions or contexts. Conclusions: Results suggest nursing perspectives are missing from the literature about toxic positivity. Identifying toxic positivity as a phenomenon in nursing work environments has potential to inform future research and theoretical work related to nursing workforce burnout, retention, and coping strategies.

No description available.

This dissertation investigated the impact of active stereoscopic 3-dimensional (3D) imagery equipment and individual differences in visuo-spatial working memory (VSWM) capacity on retention of a set of similar, novel objects (i.e., armored military vehicles). Seventy-one participants were assessed on their visuo-spatial working memory using the Visual Patterns Test (Della Sala, Gray, Baddeley, & Wilson, 1997). They were then assigned to one of four different conditions (3D high VSWM, 3D low VSWM, 2D high VSWM, 2D low VSWM) based upon their visuo-spatial working memory. Participants were then trained to identify military vehicles using a simulation that presented the training stimuli in one of two dimensionalities, i.e. two dimensional (2D) or active stereoscopic three-dimensional (3D). Testing consisted of a vehicle memory training assessment, which challenged participants to choose the correct components of each vehicle immediately after studying; a measure of retention for military vehicles which asked participants to categorize the alliance and identify previously studied vehicles; and a transfer measure using video footage of actual military vehicles. The latter measures depicted military vehicles in an array of combat situations, and participants were asked to decide on whether or not to shoot each vehicle, as well as identify the vehicles. Testing occurred immediately after training. The moderating, as well as main effects, of VSWM were assessed. The mediating/moderating effects of several experiential factors were measured as well, including: immersion, presence, engagement, flow state, and technology acceptance. Findings indicate that perceptions of the simulation experience and VSWM are strong positive predictors of performance, while 3D was not predictive, and in some instances, significantly worse than the 2D condition. These findings indicate that individual differences in visual memory and user experiences during the SBT both are predictive factors in memory tasks iv for confusable objects. The SBT designed in this study also led to robust prediction of training outcomes on the final transfer task.

This research defined and evaluated mechanical properties of prototypes created using a plaster based three-dimensional printing (3DP) system commercialized by Z Corporation. 3DP is one of the fastest growing forms of rapid prototyping. Till date, there is little or no information available on material properties of infiltrants used in 3DP. This research work evaluated and documented some of the useful information for 3DP users by determining the effect of build position, build orientation and infiltration materials on the strength of prototypes. The study was performed in three different phases to limit the processing variables and to arrive at definite conclusions on relationship between materials properties and process variables. All specimens were built on the Z Corporation Spectrum Z510. In Phase 1, effects of build location on specimen strength was studied. Phase 2 evaluated the influence of build orientation on specimen strength. System Three Clear Coat epoxy was used during both Phase 1 and 2 for infiltration. The same infiltrant was in both of these phases to limit variables. Using results of Phase 1 & 2, the effects of infiltrant material on tensile strength of prototypes was calculated in Phase 3. Seven different infiltrating materials were tested during Phase 3. These materials included 2 cyanoacrylates and 5 epoxies. The tensile strength, flexural strength, and density and porosity of the specimens were determined and correlated. In each phase six specimens were built for each test performed. Two consistent methods of infiltration were utilized to infiltrate cyanoacrylates and epoxies into the as-processed specimens. It was found that the orientation of the specimen has more of an impact on strength than position within the build platform. The layering build process of rapid prototyping creates a variance in strength depending on the build orientation. Specimens infiltrated with epoxy achieved much higher strength than the specimens infiltrated with cyanoacrylate. Cyanoacrylates may be a good choice in making color concept models; however they are not good candidate materials where strength requirement is important. The epoxies with lower viscosities demonstrated higher part strength among the materials tested.

Three-dimensional (3D) metal photonic crystals (MPCs) can exhibit interesting electromagnetic properties such as ultra-wide photonic or "plasmonic" band gaps, selectively tailored thermal emission, extrinsically modified absorption, and negative refractive index. Yet, optical-wavelength 3D MPCs remain relatively unexplored due to the challenges posed by their fabrication. This work explores the use of multi-photon direct laser writing (DLW) coupled with electroless metallization as a means for preparing MPCs. Multi-photon DLW was used to prepare polymeric photonic crystal (PC) templates having a targeted micron-scale structure and form. MPCs were then created by metallizing the polymeric PCs via wet-chemical electroless deposition. The electromagnetic properties of the polymeric PCs and the metallized structures were characterized using Fourier transform infrared spectroscopy. It is shown that metallization transforms the optical properties of the structures from those of conventional 3D dielectric PCs to those consistent with 3D MPCs that exhibit ultra-wide photonic band gaps. These data demonstrate that multi-photon DLW followed by electroless deposition provides a viable and highly flexible route to MPCs, opening a new path to metal photonic materials and devices.

Cell culturing on three-dimensional structures has increased the possibilities in tissue engineering and bioreactor research. These structures enable cells to differentiate, proliferate, mobilize, and function in a conformation that more accurately mimics in vivo conditions. Computer generated models aid in development and rapid alteration of three-dimensional cell substrates, defining their internal structure as well as their external morphology. The rapid transition from substrate design to a viable culture is imperative to quickly advance research in biomedical and tissue engineering applications. The aim of this thesis is to investigate the feasibility of a rapid prototyping process by selectively cross-linking and assembling biocompatible films. This investigation revealed that selectively cross-linking and layering gelatin films could produce a three-dimensional substrate with a defined structure after dissolving uncross-linked gelatin. The study also revealed that freeze-drying aided in the rapid dissolution of uncross-linked gelatin. The line width resolution obtained during tests was .5 mm using a template treatment method and was limited by the template construction resolution. Finally, alteration in treatment time, rinsing agitation, and rinsing temperature yielded stable films that better retained their size and shape compared to films produced in previous processes.

Modem high-performance military aircraft are subjected to rapid flight maneuvers which place great operational demands on their compression system by producing highly distorted flow to the compressor. Inlet distortion generally reduces the engine compressor stability margin and may induce compressor surge at high rotational speeds, or rotating stall at lower rotational speeds. Therefore, a computational fluid dynamics (CFD) based compressor simulation would be very useful in the design, test, and analysis process since it gives additional information with inexpensive modifications. A new CFD simulation called the Turbine Engine Analysis Compressor Code (TEACC) was designed to meet these requirements. This code solves the compressible 3D Euler equations modified to include turbomachinery source terms which simulates the effect of the compressor blades. The source terms are calculated for each blade row by the application of a streamline curvature code. A methodology was developed for calculating turbomachinery source terms and distributing them axially, radially, and circumferentially while maintaining a sensitivity to strong inlet distortion. TEACC was compared with experimental data from NASA Rotor 1 B, a transonic rotor. Experimental data from Rotor 1 B were available for comparison with TEACC results for a clean inlet and for an inlet distortion produced by a 90-degree, one-per-revolution screen. TEACC results compared very well with experimental data with a clean inlet. Comparison with experimental data with inlet distortion demonstrated TEACC's ability to characterize the compressor overall, and to accurately predict the magnitude and shape of exit total temperature and exit total pressure in the distorted region. TEACC calculated the overall character of exit total pressure and exit total temperature in the nondistorted region, identifying the location of the largest value just after the inlet distortion and the decrease in exit total values through the nondistorted region in the direction of rotation. / Ph. D.

A more robust method for solving the governing equations of a one-dimensional stage-by-stage dynamic compression system model was developed and validated. The improved method was then applied to two-dimensional post-stall models. The improvement in robustness was achieved by modeling the governing equations with upwind differencing and use of implicit time integration. A special form of upwind flux, flux difference splitting with source term treatment, FDSS, was developed for the model. A two-dimensional axisymmetric model was developed to allow post-stall modeling of split flowpath systems such as turbofans. This model was an entirely new concept. Additionally, a two-dimensional axial-circumferential model of rotating stall cell development and propagation was developed based on previous work. All of the models developed applied upwind differencing techniques to improve upon central-difference methods. / Ph. D.

An unsteady, finite-rate, one-dimensional model has been developed for the analysis for gas-turbine combustors. The basis of the model is the one-dimensional, integral form of the conservation equations for multi-species, non-equilibrium, reacting mixtures. Special procedures were devised for the flow-division of the inlet flow into primary- and annular-flows, for both straight- and reverse-flow combustors. This allows the model to handle complete combustor configurations, which at present are beyond the reach of more sophisticated CFD tools. The model was validated with a steady-state analytical solution for a basic problem, and with steady-state results from a production code applied to a production combustor. Additional calculations show the ability of the code to predict blow-out due to rich and lean mixtures, and to predict the response of a combustor to perturbations in operating and boundary conditions. / Ph. D.