OBJECTIVE: To evaluate if the firing cycles and etching conditions have an effect on the tensile bonding strength (TBS) of IPS e.max-CAD and CeltraDUO. METHODS: Lithium-disilicate (IPS e.max-CAD) ceramic blocks and zirconia reinforced lithium-disilicate (CeltraDUO) were sectioned into rectangular tiles. The tiles were randomly assigned to various treatment groups and heat treated (1, 5, or 9 firing cycles) or (0, 1 or 5 firing cycle) respectively. e.max-CAD and CeltraDUO tiles were etched for different times (20,160, 300 seconds) and (20, 50, 80 seconds) respectively with hydrofluoric-acid gel (9.6% or 5%). Titanium-pins were sand-blasted on the flat end and cemented on the etched tiles using self-adhesive resin cement (TheraCem). A vertical load of 12N was placed for 40 minutes. All the cemented specimens were stored in incubator at 37°C for 48 hours. A tensile test was performed using a mechanical testing machine (Instron-5566A). The load at failure was recorded and the TBS was calculated. The same procedure was followed on another set of 18 e.max-CAD (fired for 5 firing cycles) and 21 CeltraDUO tiles (fired for 1 firing cycle). The same cementation procedure was followed and TBS was calculated. RESULTS: The TBS of both CeltraDUO and e.max-CAD was significantly affected by etching duration and firing cycles (p<0.001), but not significantly affected by etchant concentration (p=0.31). The highest load to failure was observed around 50 and 60 seconds of etching respectively. CONCLUSION: The etching time and firing cycle directly affect the TBS of both materials whereas the etchant concentration does not. / 2021-07-15T00:00:00Z

No description available.

Indiana University-Purdue University Indianapolis (IUPUI) / Cementing of indirect restorations with resin cements generally requires the pre-treatment of dentin with an adhesive. When dual-cured or chemical-cured resin cements are used with these single-step adhesives, incompatibility issues exist. This has resulted in manufacturers making chemical changes in their products. Kerr Dental markets a new resin cement, Nexus Third generation (NX3), which utilizes a proprietary redox system different from the second generation of composite luting agent (NX2). The aim of this study was to evaluate microtensile bond strength and mode of failure of NX3 and NX2 with two different adhesive systems (total-etch and self-etch) after 1 week and after 3 months of storage. Methods: Sixty-four non-carious teeth were sectioned to expose the dentin using a low-speed saw. Dentin surfaces were ground with 320-grit SiC paper. The adhesives Optibond Solo Plus (SOL), and Optibond All In One (AIO) were applied, and resin cements (NX2, NX3) were used to lute 4-mm composite discs to the treated dentin surfaces. Microtensile bond strength was determined at 1 week (IM) and after 3 months (3MON) of storage using a universal testing machine (MTS). All specimens were examined under the stereomicroscope to determine the mode of failure. Random specimens from each failure group were examined using scanning electron microscopy. Statistical Analysis: Comparisons between the treatment combinations for differences in microtensile bond strength were performed using Weibull-distribution survival analysis. Comparisons between the treatment combinations for differences in the failure mode were performed using Fisher’s Exact tests. The group NX3 SOL IM (30.5 MPa) had significantly higher bond strength than NX3 SOL 3MON (13.4 MPa); NX3 AIO IM (11.3MPa); NX3 AIO 3MON (8.2 MPa; NX2 AIO 3MON (5.8 MPa); NX2 SOL IM (6.3 MPa), and NX2 SOL 3MON (3.2 MPa). The group NX2 AIO IM (19.3 MPa) was not significantly different from NX3 SOL IM. The group NX2 SOL 3MON and group NX2 SOL IM had a significantly higher percentage of teeth with mixed failure than all of the other groups. None of the other groups had significantly different failure mode. The group NX3 SOL IM had 90-percent beam survival beyond 17 MPa, and NX2 AIO IM had 50 percent of beams surviving beyond 17 MPa, a better performance. For all the other groups, more than 50 percent of beams failed below 17 MPa. Results show high evidence of degradation for all groups considered in this investigation. The use of these types of cement adhesive combinations in clinical situations should be used with this understanding.

We approximate the vibrational energies of the symmetric and asymmetric stretches of the hydrogen bonds of the molecules H_3O_2^- and H_5O_2^+ by applying an improvement to the standard time-independent Born-Oppenheimer approximation. These two molecules are symmetric around a central hydrogen which participates in hydrogen bonding. Unlike the standard Born-Oppenheimer approximation, this approximation appropriately scales the hydrogen nuclei differently than the heavier oxygen nuclei. This results in significantly more accurate approximations for the stretching vibrational energies, which we compare to experimental measurements. / Master of Science

<p> This thesis presents the results of an attempt to study the chemical bond in terms of the three-dimensional electronic charge distribution and the force which this charge distribution exerts on the nuclei. The homonuclear diatomic molecules Li2, B2, C2, N2, O2, and F2 are discussed in terms of covalent binding while the heteronuclear diatomic molecules LiF and LiH are discussed in terms of ionic binding.</p> / Thesis / Doctor of Philosophy (PhD)

<p> This thesis deals with 0-substituted carbenium ions. In particular, the relationship between the pattern of substitution and the nature of the charge distribution in the ion are probed by looking at the effects of systematic substituent change on bond distances.</p> <p> The model system employed in this investigation is the 1,3-dioxolan-2-ylium ion. A series of five ions were investigated by the preparation of single crystals which were studied using x-ray crystallography.</p> <p> The carbon oxygen bond distances around the five-membered dioxolanylium ring were found to be sensitive to changes in methyl substitution at position 4 of the ring. As methyl substitution at this position was increased systematically, an increase in the C4-03 carbon oxygen bond distance was observed.</p> <p> Changes in the substituent at position 2 of the dioxolanylium ring also had an effect on carbon oxygen bond distances but of a lesser magnitude than those brought about by methyl substitutions at position 4. The importance of these changes in structure are discussed in terms of the charge distribution in the cations.</p> / Thesis / Master of Science (MSc)

<p> Carbocyclic and heterocyclic compounds are ubiquitous in nature. Therefore, the discovery and development of new ring forming reactions are of paramount interest to synthetic organic chemists. Recently, the intramolecular cyclization of reactive intermediates, such as anions, cations, and radicals have provided a number of new methods by which known and novel ring systems can be constructed. Cyclizations involving tandem, or multiple sequences have gained considerable popularity due to their high overall efficiency and remarkable speed by which these processes can yield complex polycyclic ring systems.</p> <p> Carbenes are another interesting class of reactive intermediates which undergo characteristic reactions. The cyclization reactions of carbenes have not been studied to a significant extent. In particular, the work described in this thesis outlines the only study of the intramolecular cyclization of dioxycarbenes onto a tethered alkyne moiety.</p> <p> The first section of this dissertation details the development of a convenient new class of thermal dioxycarbene precursors, dioxyoxadiazolines I, which display many significant advantages over previously used sources of dioxycarbenes ll. (See Diagram in Thesis)</p> <p> The second section of this dissertation details the use of dioxyoxadiazolines possessing a tethered triple bond for the thermal generation of dioxycarbenes III which are capable of intramolecular cyclization. It was found that the cyclization of a dioxycarbene onto a tethered triple bond results in the regioselective generation, of another reactive intermediate, a 3,3-dioxyvinylcarbene (IV or V, depending on the nature of R'), which can undergo a number of interesting intermolecular reactions. This approach leads to the rapid construction of some interesting and rather complex polycyclic heterocyles which are, in many cases, obtained with high regioselectivity and sometimes even high stereoselectivity. (See Diagram in Thesis)</p> <p> The results described in this thesis mark the discovery and development of a new synthetic methodology which may, by appropriate choice of the starting material, provide a valuable tool for the rapid and selective synthesis of a number of heterocyclic ring systems.</p> / Thesis / Doctor of Philosophy (PhD)

This thesis involves the consideration of the reinforced concrete beam as a composite beam with incomplete interaction. The influence of bond slip and loading condition on the formation of cracks is studied analytically. / Thesis / Master of Engineering (ME)

<p dir="ltr">In computer-aided drug discovery, methods that are approximate, but computationally inexpensive play an essential role during the initial phase of the discovery process. Although often inaccurate, they enable the screening of vast drug libraries to identify potential inhibitors with favorable activities, before large amounts of computational resources could be dedicated to studying these individual molecules. This thesis presents<b> </b>such an approach, based on the concept of hydrogen bond wrapping, to study protein-ligand interactions in the context of drug discovery. The ‘wrapping’ refers to the tendency of hydrophobic groups to surround a hydrogen bond in water, leading to its desolvation, thereby stabilizing it.</p><p dir="ltr">Herein, a molecular descriptor was employed, which quantifies the extent of hydrophobic wrapping around a protein’s backbone hydrogen bonds (BHBs) and could help speed up the discovery process by providing cues for the design or optimization of inhibitors. Additionally, these insights could help tailor not just the binding affinity of inhibitors, but also their specificity toward an intended target protein. The human transmembrane protease serine 2 (TMPRSS2) was used as an illustrative target protein due to the pressing need for COVID-19 therapeutics, and since the current understanding of the binding mechanisms of known TMPRSS2 inhibitors is limited.</p><p dir="ltr">Molecular docking with a Generalized Born - surface area (GBSA) scoring function was first performed to virtually screen for TMPRSS2 inhibitors. The molecular descriptor was then used to analyze the change in wrapping groups of TMPRSS2 BHBs due to docked ligands, with the aim of identifying BHBs with a high propensity for desolvation. The BHBs involving residues Cys437, Gln438, Asp440, and Ser441 of TMPRSS2 were seen to have some of the largest average increases in wrapping. These general results were also compared to results from docking of the known TMPRSS2 inhibitors, camostat, and nafamostat.</p><p dir="ltr">The data generated from docking were then used to examine potential applications of the wrapping molecular descriptor using machine learning techniques: (i) for prediction of the solvent-accessible surface area term ΔG_sa of the GBSA score using regression and (ii) for classifying the solvent interactions of a TMPRSS2-inhibitor complex as favorable or unfavorable. The descriptor was seen to be only weakly related to ΔG_sa; the best-performing regression model had a Pearson correlation coefficient of 0.76 between the predictions and the actual values. The ability of the descriptor to classify solvent interactions was more satisfactory, with a highest value for area under the receiver operating characteristic curve of 0.75.</p><p dir="ltr">The descriptor was then used to analyze the effect of inhibitor binding on the dynamics of TMPRSS2 BHBs. For this, molecular dynamics simulation was carried out for the uncomplexed TMPRSS2, as well as its complex with known inhibitors and hit molecules from docking. The binding of these ligands was seen to improve the stability of TMPRSS2; certain BHBs which were unstable or not formed in the uncomplexed case, showed increased stability. These prominently included a couple of BHBs identified from docking as having gained a large increase in wrapping. The improved stability coincided with an increase in wrapping groups in several cases. The descriptor also successfully rationalized the desolvation of a few BHBs due to inhibitor binding.</p><p dir="ltr">This work demonstrates the potential application of the concept of hydrogen bond wrapping in understanding the mechanism of inhibitor binding and the resultant desolvation effects on a protein’s BHBs, without computationally expensive calculations. While the analysis methods require further improvement, the wrapping descriptor shows promising results and could be developed into a simple, yet powerful tool for drug discovery.</p>

Mental health practitioners who incorporate animal-assisted interventions into clinical practice harness the human-animal bond for therapeutic benefit. According to the Animal-Assisted Therapy in Counseling Competencies, practitioners have a duty to understand the complex relational processes within animal-assisted interventions in counseling (AAI-C). These bonding processes may resemble that of an attachment bond in which the client desires to maintain closeness to the practitioner and therapy animal as a result of feeling safe and secure. Researchers studying attachment in the human-animal bond have stated that attachment processes may occur within other human-animal relationships, such as between a guardian and a companion animal. However, there is no empirical research on the attachment processes occurring between humans and therapy animals in AAI-C or how these processes affect the bond between the practitioner and client. A component of the working alliance, maintaining a quality bond can improve treatment outcomes in counseling. Therefore, the purpose of this quantitative study was to examine how attachment to a therapy animal impacts the attachment bond between a mental health practitioner and client. Participants completed an online survey with four measures to study the following: (a) client attachment to the therapy animal, (b) practitioner attachment to the therapy animal, (c) the bond between the practitioner and client, and (d) the impact of utilizing an animal in counseling sessions. Data analyses included a multiple regression to determine how practitioners' perceptions of the attachment processes within AAI-C best explain the bond with their clients. Descriptive analysis revealed that practitioners perceived high quality bonding within AAI-C, particularly in their own attachment to the therapy animal. Results of the multiple regression indicated practitioners' attachment to the therapy animal was a significant predictor of the working alliance and bond between the practitioner and client. Practitioners who perceived themselves as extremely skilled in working with the clients' presenting issue also had a statistically significant effect on the working alliance and bond when compared to practitioners who felt less skilled. Implications for practitioners and counselor educators are provided. Limitations and areas of future research are also discussed. / Doctor of Philosophy / Mental health practitioners who incorporate animal-assisted interventions into clinical practice harness the human-animal bond for therapeutic benefit. According to the Animal-Assisted Therapy in Counseling Competencies, practitioners have a duty to understand the complex relational processes within animal-assisted interventions in counseling (AAI-C). These bonding processes may resemble that of an attachment bond in which the client desires to maintain closeness to the practitioner and therapy animal as a result of feeling safe and secure. Researchers studying attachment in the human-animal bond have stated that attachment processes may occur within other human-animal relationships, such as between a guardian and a companion animal. However, there is no practical research on the attachment processes occurring between humans and therapy animals in AAI-C or how these processes affect the bond between the practitioner and client. A component of the working alliance, maintaining a quality bond, can improve treatment outcomes in counseling. Therefore, the purpose of this quantitative study was to examine how attachment to a therapy animal impacts the attachment bond between a mental health practitioner and client. Participants completed an online survey with four measures to study the following: (a) client attachment to the therapy animal, (b) practitioner attachment to the therapy animal, (c) the bond between the practitioner and client, and (d) the impact of utilizing an animal in counseling sessions. Data analyses included a multiple regression to determine how practitioners’ perceptions of the attachment processes within AAI-C best explain the bond with their clients. Descriptive statistics revealed that practitioners perceived high quality bonding within AAI-C, particularly in their own attachment to the therapy animal. Results of the multiple regression indicated practitioners’ attachment to the therapy animal influenced the working alliance and bond between the practitioner and client. Practitioners who perceived themselves as extremely skilled in working with the clients’ presenting issue also had an effect on the working alliance and bond when compared to practitioners who felt less skilled. Implications for practitioners and counselor educators are provided. Limitations and areas of future research are also discussed.