Background: New dental restorative material, “Cention Forte” and “Admira Fusion” have been available on the market for quite some time but are still new in comparison with traditional resin-based composite, “Ceram.x Spectra ST” and glass ionomer cement, “GC Fuji II LC”.  Aim: To compare the flexural strength, elemental composition, and porosity of new dental restorative materials (Cention Forte, Admira Fusion) with existing ones (Ceram.x Spectra ST, GC Fuji II LC).   Methods: Three-point bending test and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analysis was used to compare the flexural strength and composition among Cention Forte, Ceram.x Spectra ST, GC Fuji II LC and Admira Fusion. 10 test specimens were used for each material, 40 in total. The dimension of the test specimens were l (25 ± 2) mm x b (2,0 ± 0,1) mm x h (2,0 ± 0,1) mm. The statical analysis was performed with one-way ANOVA followed by Bonferroni’s post-hoc test.  Results: The three-point bending test showed that Cention Forte and Ceram.x Spectra ST had the highest mean flexural strength between the 4 materials tested, whereas GC Fuji II LC had the lowest. Admira Fusion had an intermediate value. SEM-EDS showed significant differences in material density and composition, it was seen that Ceram.x Spectra ST and Admira Fusion had the lowest porosity while GC Fuji II LC had the highest porosity.  Conclusion: It can be concluded that Cention Forte and Ceram.x Spectra ST are the strongest dental materials among the ones tested, with high flexural strength values. Therefore, they may be more suitable for use in high stress-bearing areas. GC Fuji II LC showed the lowest flexural strength values, making it less suitable for use in such areas. Admira Fusion showed intermediate values, making it a good option for applications with moderate stress-bearing requirements. SEM-EDS analysis showed that Ceram.x Spectra ST and Admira Fusion had the lowest amount of porosity, whereas GC Fuji II LC had the highest. The presence of these porosities weakens the material, a higher number of porosities implies lower flexural strength values.

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The entorhinal cortex is reciprocally connected with both neocortical sensory areas and the hippocampal formation, and is thought to play a pivotal role in learning and memory. Changes in synaptic strength are thought to provide the major neurophysiological basis for memory formation, but little is known about synaptic plasticity in the entorhinal cortex. The objectives of this research were to provide a basis for the interpretation of evoked potentials recorded from the entorhinal cortex following pyriform (primary olfactory) cortex stimulation 𝘪𝘯 𝘷𝘪𝘷𝘰, and to determine the conditions under which synaptic enhancements in this pathway may occur and contribute to lasting changes in the processing of olfactory information. The synaptic currents which generate field potentials in the entorhinal cortex following pyriform cortex and medial septal stimulation were first localized to the superficial layers of the entorhinal cortex using current source density analysis techniques in the anesthetized rat. This allowed changes in the strength of these synaptic inputs to be monitored in the awake rat by measuring evoked field potential amplitudes at a single cortical depth. Long-term synaptic potentiation (LTP) in this pathway was reliably induced following stimulation of the pyriform cortex with either epileptogenic stimuli, or with prolonged subconvulsive high-frequency trains. Further, stimulation which results in short-term frequency potentiation effects, was found to increase the amount of LTP induced. Concurrent stimulation of the medial septum at a frequency similar to that of the endogenous theta rhythm also resulted in a cooperative enhancement of the LTP produced. Computational modelling techniques were then used to formalize the heterosynaptic contribution of frequency potentiating medial septal inputs to Hebbian synaptic modification in entorhinal cortex. These results indicate that the frequency of rhythmic activity in sensory afferents and the activity of the medial septum may play critical roles in the regulation of synaptic plasticity in the entorhinal cortex. / Thesis / Doctor of Philosophy (PhD)

In addition to immediate elastic deformations, concrete undergoes time-dependent deformations that must be considered in design. Creep is defined as the time-dependent deformation resulting from a sustained stress. Shrinkage deformation is the time-dependent strain that occurs in the absence of an applied load. The total strain of a concrete specimen is the sum of elastic, creep, and shrinkage strains. Several test beams for the Pinner's Point Bridge have been produced by Bayshore Concrete Products Corp., in Cape Charles, VA. These beams feature high strength concrete mix designs with specified 28-day compressive strengths of 55.2 MPa (8,000 psi) and 69.0 MPa (10,000 psi). These test beams were equipped with thermocouples to track interior concrete temperatures, and vibrating wire gages placed at the center of prestressing to record changes in strain. Laboratory creep and shrinkage testing was conducted on specimens prepared with identical materials and similar mixture proportions to those used at Bayshore. The temperature profile from the test beams during steam curing was used to produce match-cured specimens for laboratory testing. Two match cure batches were produced, along with two standard cure batches. Creep specimens from each batch were placed in the creep room and loaded to 30 percent of their after-cure compressive strength. The creep room had a temperature of 23.0 ± 1.7 °C (73.4 ± 3 ºF) and relative humidity of 50 ± 4 %. Companion shrinkage specimens were also placed in the creep room. Measurements were taken on the creep and shrinkage specimens using a Whittemore gage. Four cylinders were also equipped with embedded vibrating wire gages (VWGs) so that the interior and exterior strains could be compared. The Whittemore and VWG elastic and creep strains were similar, while the VWGs recorded significantly less shrinkage. The measured creep and shrinkage strains were compared to seven different models to determine which model was the most accurate. The models considered were ACI 209, ACI 209 modified by Huo, CEB Model Code 90, AASHTO-LRFD, Gardner GL2000, Tadros, and Bazant B3. The ACI 209 modified by Huo was most accurate in predicting time-dependent strains. / Master of Science

Hand and finger force data are used in many settings, including industrial design and indicating progress during rehabilitation. The application of appropriate work design principles, during the design of tools and workstations that involve the use of the hand and fingers, may minimize upper extremity injuries within the workplace. Determination and integration of force capabilities and requirements is an essential component of this process. Available data in the literature has focused primarily on whole-hand or multi-digit pinch exertions. The present study compiled and examined maximal forces exerted by the fingers in a variety of couplings to both enhance and supplement available data. This data was used to determine whether finger strength could be predicted from other strength measures and anthropometry. In addition, this study examined whether exerted finger forces could be estimated using surface electromyography obtained from standardized forearm locations. Such processes are of utility when designing and evaluating hand tools and human-machine interfaces involving finger intensive tasks, since the integration of finger force capabilities and task requirements are necessary to reduce the risk of injury to the upper limbs. Forces were measured using strain gauge transducers, and a modification of standard protocols was followed to obtain consistent and applicable data. Correlations within and among maximum finger forces, whole-hand grip force, and anthropometric measures were examined. Multiple regression models were developed to determine the feasibility of predicting of finger strength in various finger couplings from more accessible measures. After examining a wide variety of such mathematical models, the results suggest that finger strength can be predicted from easily obtained measures with only moderate accuracy (R²-adj: 0.45 - 0.64; standard error: 11.95N - 18.88N). Such models, however, begin to overcome the limitations of direct finger strength measurements of individuals. Surface electrodes were used to record electromyographic signals collected from three standardized electrode sites on the forearm. Multiple linear regression models were generated to predict finger force levels with the three normalized electromographic measures as predictor variables. The results suggest that standardized procedures for obtaining EMG data and simple linear models can be used to accurately predict finger forces (R²-adj: 0.77 - 0.88; standard error: 9.21N - 12.42N) during controlled maximal exertions. However, further work is needed to determine if the models can be generalized to more complex tasks. / Master of Science

This thesis studies the present methods used to predict the ultimate tripping strength of stiffened panels under compressive axial stress. The current methods involve the use of a bifurcation, or eigenvalue, approach to predicting failure stress. The effects of initial transverse eccentricity of the stiffener are ignored using such a method. Six panels were modeled and tested with ABAQUS, a finite element software package, and the results were compared to output from ULSAP, a closed-form ultimate strength analysis program. The ultimate strengths predicted by ABAQUS changed with the influence of initial deflection of the stiffener flange, while the results from ULSAP did not change. This thesis attempts to use beam-column analysis on the imperfect stiffener flange to predict the tripping strength. It was determined that the procedure presented in this thesis does not accurately model the true failure mode of stiffeners in tripping. The resulting ultimate strengths are extremely conservative and neglect the importance of the stiffener web's role in tripping. Future work is recommended to expand on these findings and to incorporate the influence of the stiffener web into a beam-column solution. / Master of Science

The objective of this research was to investigate the effect of applied compressive strain in various environments, on the strength and stiffness of compressed wood samples. It is believed that transverse compression of wood at specific conditions of temperature and moisture will result in improved mechanical properties, which can be attributed to increased density and perhaps other physical or chemical changes. Specimens of both mature and juvenile southern pine (Pinus taeda) and yellow-poplar (Liriodendron tulipifera) were compressed radially at three different temperature, and moisture content conditions relevant to the glass transition of wood. Ultimate tensile stress and longitudinal modulus of elasticity were obtained by testing compressed, uncompressed and control samples in tension parallel-to-grain. Strain measurements were performed using laboratory-built clip-on strain gauge transducers. Results of the tensile tests have shown an increase in the ultimate tensile stress and modulus of elasticity after all densification treatments. Scanning electron microscopy was employed for observing changes in cellular structure of densified wood. Existence of the cell wall fractures was evaluated using image processing and analysis software. Changes in cellular structure were correlated with the results of the tensile test. Chemical composition of wood samples before and after desorption experiments was determined by acid hydrolysis followed by high performance liquid chromatography (HPLC). The results of the chemical analysis of the wood specimens did not reveal significant changes in chemical composition of wood when subjected to 160 °C, pure steam for up to 8 hours. The results of this research will provide information about modifications that occur during wood compression and will result in better understanding of material behavior during the manufacture of wood-based composites. In the long run, modification of wood with inadequate mechanical properties can have a significant effect on the wood products industry. Low density and juvenile wood can be used in new high-performance wood-based composite materials instead of old-growth timber. / Master of Science

One scheme for reliability-based design that is growing in popularity for civil and naval applications is the load and resistance factor design (LRFD). Our goal in this research is the development of a simulation to predict the remaining strength of structural composites subjected to variable fatigue loading and environmental exposure. The results of this simulation can then be used in LRFD to determine appropriate material factors of safety for engineering design applications. The work so far focuses on modeling the response of the material to fatigue damage only. A general phenomenological modeling approach is described and applied in two experimental studies using E-glass/vinyl ester composite materials. Strength distributions are modeled using Weibull statistics and residual strength is modeled using a strength-life equal rank assumption and a Monte-Carlo style simulation. The model provides good residual strength distribution fits to constant amplitude fatigue data and worked well for ordered block spectrum loading using a 735,641 cycle, 22 stress level spectrum. However, applying a randomized spectrum produced unexpected results with every specimen failing after 200,000 to 400,000 cycles while the model predicts identical residual strength when compared with the block loading case. This work points to a need for focus on developing a better understanding of load order impacts in design of composite structures based on constant amplitude fatigue tests. A future approach toward more detailed micro-mechanics fatigue damage modeling is suggested to enable better modeling of residual strength of laminates subjected to random loading fatigue. / Master of Science