Total Bond Strength Research Articles

Stronger maternal social bonds and higher rank are associated with accelerated infant maturation in Kinda baboons

Social relationships are critical components of health and fitness for humans and other animals. For female-philopatric species, affiliative relationships among females (kin and nonkin alike) can influence components of fitness that include individual survival, interbirth interval and offspring survival. Affiliative relationships with males have attracted somewhat less attention, with most studies focusing on female–male relationships as adaptations for infanticide avoidance. Here, we use 8 years of behavioural data on Kinda baboons, Papio kindae , to assess whether maternal social relationships—both among females and between females and males—affect infant survival, interbirth interval and the pace of infant development. Kinda baboons are an ideal system for these analyses because males and females form strong relationships outside of the periovulatory period and in the absence of obvious infanticide threat. We calculated social metrics that reflected dominance status, total social integration and social bond strength and paired these metrics with data on offspring survival, interbirth interval (IBI) duration and infant behavioural maturation. Neither dominance rank nor sociality had a significant effect on interbirth interval or survival, but higher rank and the stronger affiliative relationships between a female and her top female and top male social partners predicted more rapid infant behavioural maturation. These results suggest that maternal dominance and sociality may confer advantages related to infant development and independence that ultimately may permit females to more quickly invest in subsequent offspring and point to advantages of relationships with males outside of lowering infanticide threat. • Kinda baboon female–male bonds persist outside of fertility or infanticide threat. • Social bonds did not affect interbirth interval or infant survival and growth. • Dominance and affiliative bonds predicted more rapid infant development. • Top-partner bonds were the strongest predictors of infant development. • Strong maternal bonds with females and males enhanced infant development.

Principles Guiding the Square Bonding Motif Containing a Pair of Chalcogen Bonds between Chalcogenadiazoles.

The bonding motif adopted by a dimer of chalcogenadiazole molecules is characterized by a pair of equivalent Ch···N chalcogen bonds. Quantum calculations show that the interaction energy is substantial, varying between 4 kcal/mol for Ch = S and 17 kcal/mol for Te. The interaction is cooperative in that the total bond strength is greater than either chalcogen bond individually. Neither the addition of a phenyl ring nor the addition of a pair of cyano substituents to the diazole ring has much influence on this binding. Removal of one N from the diazole weakens the binding, and addition of two nitrogens has little effect. The largest perturbation arises with three N atoms in each ring, for which the binding energy increases by some 25%. The ring size plays a minor role in most cases, although a near doubling of bond strength occurs if there are two N atoms present on a four-membered ring.

First-principles study of vacancy ordered structures, mechanical properties and electronic properties of ternary Hf-C-N system

The thermal-mechanical properties of transition metal carbonitrides can be affected by the concentration and ordering of vacancies besides the C/N atomic ratio. However, there are few reports on the vacancy ordered structure of ternary transition metal carbonitrides. In the present paper, the first-principles method is used to study the vacancy ordered structures, mechanical properties, electronic properties and the effect of vacancies on the ternary Hf-C-N system. Firstly, the crystal structures of Hf-C-N system is examined by the first-principles and evolutionary algorithms implemented in USPEX under ambient pressure, and eight thermodynamical stable vacancy ordered structures are found, each of which has a rock-salt structure, and is also dynamical and mechanical stable, which are verified by the calculations of their phonon dispersion curves and elastic constants. The vacancies are occupied at the [Hf<sub>6</sub>] octahedral interstices, which replace the positions of non-metal atoms. Their crystallographic data such as space group, lattice constants are also predicted. To the best of our knowledge, there is no report on the Hf-C-N vacancy ordered structures and these structures investigated here in this work are all found for the first time. Then their mechanical properties are calculated. The Hf-C-N vacancy ordered structures all have very high bulk, shear and elastic modulus and hardness. It is found that except for C∶N = 1∶4, for the Hf-C-N system with the same C/N ratio the moduli, Vickers hardness values, and Pugh’s ratios decrease with the increase of the concentration of vacancy. However, the Vickers hardness of Hf<sub>6</sub>CN<sub>4</sub> (the concentration of vacancy is equal to 1/6) is higher than that of Hf<sub>5</sub>CN<sub>4</sub> (no vacancy), that is so-called vacancy hardening. Finally, the electronic density of states and the crystal orbital Hamilton populations are calculated. The chemical bonding of Hf-C-N vacancy ordered structure is analyzed, which is a mixture of covalence and metallic and is similar to that of binary transition metal carbides and nitrides. With the increase of the concentration of vacancy, the total bond strength decreases, and then the modulus decreases for Hf-C-N compound.

N-Heterocyclic Silylenes as Ligands in Transition Metal Carbonyl Chemistry: Nature of Their Bonding and Supposed Innocence.

A study on the reactivity of the N‐heterocyclic silylene Dipp2NHSi (1,3‐bis(diisopropylphenyl)‐1,3‐diaza‐2‐silacyclopent‐4‐en‐2‐yliden) with the transition metal complexes [Ni(CO)4], [M(CO)6] (M=Cr, Mo, W), [Mn(CO)5(Br)] and [(η 5‐C5H5)Fe(CO)2(I)] is reported. We demonstrate that N‐heterocyclic silylenes, the higher homologues of the now ubiquitous NHC ligands, show a remarkably different behavior in coordination chemistry compared to NHC ligands. Calculations on the electronic features of these ligands revealed significant differences in the frontier orbital region which lead to some peculiarities of the coordination chemistry of silylenes, as demonstrated by the synthesis of the dinuclear, NHSi‐bridged complex [{Ni(CO)2(μ‐Dipp2NHSi)}2] (2), complexes [M(CO)5(Dipp2NHSi)] (M=Cr 3, Mo 4, W 5), [Mn(CO)3(Dipp2NHSi)2(Br)] (9) and [(η 5‐C5H5)Fe(CO)2(Dipp2NHSi‐I)] (10). DFT calculations on several model systems [Ni(L)], [Ni(CO)3(L)], and [W(CO)5(L)] (L=NHC, NHSi) reveal that carbenes are typically the much better donor ligands with a larger intrinsic strength of the metal–ligand bond. The decrease going from the carbene to the silylene ligand is mainly caused by favorable electrostatic contributions for the NHC ligand to the total bond strength, whereas the orbital interactions were often found to be higher for the silylene complexes. Furthermore, we have demonstrated that the contribution of σ‐ and π‐interaction depends significantly on the system under investigation. The σ‐interaction is often much weaker for the NHSi ligand compared to NHC but, interestingly, the π‐interaction prevails for many NHSi complexes. For the carbonyl complexes, the NHSi ligand is the better σ‐donor ligand, and contributions of π‐symmetry play only a minor role for the NHC and NHSi co‐ligands.

Development of discrete meso-scale bond model for corrosion damage at steel-concrete interface based on tests with/without concrete damage

Rebar corrosion can lead to significant deterioration in bond strength between steel and concrete. However, since confinement is lost as the concrete cracks, the changes in frictional bonding and mechanical bonding resulting from corrosion remain unclear and there is a need for an efficient tool that can evaluate the bond performance of corroded concrete structures. In this study, an innovative pull-out test is used to study changes in bonding in reinforced concrete after rebar corrosion, then a discrete meso-scale model based on the Rigid Body Spring Model (RBSM) is developed to simulate the observed bond behavior. To isolate the effects of concrete cracking, after an initial pull-out test, the corroded rebars are obtained and used as the reinforcement in newly cast sound specimens that are subject to a further pull-out test. A corrosion acceleration method is used to obtain corroded rebars. Different types of reinforcement (round rebars and deformed rebars) are studied. The results are used to study changes in frictional bonding and mechanical bonding at different degrees of corrosion. It is found that, without concrete cracking, the frictional bond in specimens with both round and deformed rebars significantly increases with the amount of corrosion, while total bond strength of specimens with deformed bar is almost unchanged because mechanical bonding is weakened. In the presence of concrete cracking, for specimens reinforced with a corroded round rebar, bond capacity increases initially (up to 3% corrosion) and then falls as corrosion increases, while bonding in those with a corroded deformed rebar shows a consistent decrease. In the RBSM-based simulations, the effect of corrosion is modeled by adjusting springs at the corroded interface. Constitutive models of shear and normal springs are developed to simulate corrosion and reflect the changes on frictional and mechanical bonding. Simulated results for load-displacement relationship, pull-out capacity and crack pattern are in good agreement with the experimental results. The numerical simulation is used to visualize internal stress development and strain distribution along the rebar as the degree of corrosion increases, a result that cannot be obtained by experimental methods. The results demonstrate that RBSM is a useful tool for evaluating the mechanical performance of corroded reinforced concrete structures.

Bactericidal and Bioactive Dental Composites.

Aim: Antimicrobial and bioactive restorative materials are needed to develop a bacteria free environment and tight bond with the surrounding tissue, preventing the spread of secondary caries and thus extending the lifetime of dental restorations. The characteristic properties of new dental bioactive and antibacterial composites are presented in this work. The new composites have been microstructurally characterized and both long and short term properties have been studied.Methods: The Ag-doped sol-gel derived bioactive glass (Ag-BG) was incorporated into resin composite in concentrations 5, 10, and 15 wt.%, to fabricate new Ag-doped bioactive and antibacterial dental composites (Ag-BGCOMP). The microstructural properties and elemental analysis of the developed Ag-BGCOMP was observed. The total bond strength (TBS) was measured immediately and after long term of immersion in medium using microtensile testing. The capability of Ag-BGCOMPs to form apatite layer on their surface after immersion in Simulated Body Fluid (SBF) as well as the bacteria growth inhibition in a biofilm formed by Streptococcus mutans (S. mutans) were evaluated.Results: Homogeneous distribution of Ag-BG particles into the resin composite was observed microstructurally for all Ag-BGCOMPs. The TBS measurements showed non-statistically significant difference between control samples (Ag-BG 0 wt.%) and Ag-BGCOMP specimens. Moreover, the total bond strength between the surrounding tooth tissue and the material of restoration does not present any statistically significant change for all the cases even after 3 months of immersion in the medium. The bioactivity of the Ag-BGCOMPs was also shown by the formation of a calcium-phosphate layer on the surface of the specimens after immersion in SBF. Antibacterial activity was observed for all Ag-BGCOMPs, statistically significant differences were observed between control samples and Ag-BGCOMPs. Accordingly, the number of dead bacteria in the biofilm found to increase significantly with the increase of Ag-BG concentration in the Ag-BGCOMPs.Conclusions: New resin composites with antibacterial and remineralizing properties have been manufactured. Characterization of these materials provides a rationale for future clinical trials to evaluate clinical benefits and outcomes in comparison with currently used dental materials.Significance: The new developed composites could ultimately prevent restoration failure and could advance patients' wellbeing.

Designing dental composites with bioactive and bactericidal properties.

The aim of this work was to fabricate and evaluate new antibacterial and bioactive composites capable of strictly controlling oral bacteria, enhancing apatite layer formation and retaining their mechanical properties. A new Ag-doped bioactive glass (Ag-BG) was incorporated into flowable dental composite (COMP) in different concentrations (1, 5, and 15 wt.%) in order to fabricate new combined bioactive and antibacterial composite materials (Ag-BGCOMPs). The antibacterial properties, bioactivity, and total bond strength of the Ag-BGCOMPs were evaluated. The bioactivity of the Ag-BG was confirmed after its immersion in simulated body fluid (SBF). The total bond strength between the surrounding tooth tissue and the new composites or the control (dental composite alone) has not shown any statistically significant difference in the performed pilot study. Antibacterial activity was observed against Escherichia coli (E. coli) and Streptococcus mutans (S. mutans) for the Ag-BGCOMP 5 wt.% and 15 wt.% but not for the Ag-BGCOMP 1 wt.% or the control. This work contributes to our long term aim which is the fabrication of dental materials capable of reducing bacteria invasion and enhancing remineralization of the surrounding dental tissues. We anticipate that these new composites could ultimately prevent restoration failure by inhibiting the formation of secondary caries and by remineralizing the hard tissues surrounding tooth lesions.

The selectivity of diglycolamide (TODGA) and bis-triazine-bipyridine (BTBP) ligands in actinide/lanthanide complexation and solvent extraction separation - a theoretical approach.

Theoretical calculations (density functional theory with the scalar relativistic ZORA Hamiltonian) have been performed to obtain the energy and Gibbs free energy of formation of cationic 1 : 3 complexes of americium(iii) and europium(iii) with a tri-O-dentate diglycolamide ligand TEDGA (a model of TODGA extractant), as well as the free energy of their partition between water and an organic diluent. The distribution of electron density over the atoms, bonds, and molecular orbitals was analyzed by means of Mulliken population analysis, the localization procedure of natural bond orbitals, and the Quantum Theory of Atoms-in-Molecules. The stabilities of both [M(TEDGA)(3)](3+) complexes are similar to each other. On the other hand, our recent data for a similar pair of cationic Am/Eu complexes with a softer (HSAB) tetra-N-dentate ligand C2-BTBP show that the [Am(C2-BTBP)(2)](3+) complex is significantly more stable in aqueous solution than its Eu counterpart. The decisive factor stabilizing the Am(3+) complexes over their Eu(3+) analogues is the charge transfer from the ligands, somewhat greater on the 6d(Am(III)) than on 5d(Eu(III)) orbitals. The covalency of M-N bonds in the [M(C2-BTBP)(2)](3+) complexes is greater than that of M-O bonds in [M(TEDGA)(3)](3+), but the latter is not negligible, in particular in the bonds with the oxygen atoms of the amide groups in TEDGA. The analysis of charge distribution over the whole molecules of the complexes shows that the TEDGA molecule is not hard as expected, but a relatively soft Lewis base, only slightly harder than BTBP. This conclusion has been confirmed by the calculation of the chemical hardness of the ligands. Moreover, the comparison of the results of bonding analysis with the calculated energies of complex formation in water and in the gas phase allows us to conclude that the population analysis, QTAIM topological parameters, and SOPT stabilization energy, as well as Wiberg and overlap-weighted NAO indices are the tools for analyzing the covalency rather than the total bond strength.

Load-reversed push-out tests on rectangular CFST columns

Load-reversed push-out tests have been carried out on 6 rectangular concrete-filled steel tubular (CFST) columns with the aim of investigating the nature of the bond between the concrete infill and the steel tube, the contribution of each bond stress component (i.e. chemical adhesion, microlocking and macrolocking) and the development of macrolocking within four half-cycles of loading. The contribution of microlocking to the total bond strength was obtained from the comparison between the ultimate strength of normal specimens and lubricated specimens, which also revealed the detrimental effect of lubrication on the bond strength. The macrolocking contribution was obtained from the comparison between the ultimate strength achieved in the first half-cycle of loading τu1 and the ultimate strength achieved in the third half-cycle of loading τu3 of the non-lubricated specimens. The developed bond mechanisms were explained and details of the interface bond stress distribution were obtained from the recorded axial strain gradients in the steel tube. Finally, the concept of a critical shear force transfer length was introduced, and its implications on practical design discussed.

Bond between galvanized steel and concrete prepared with limestone aggregates

PurposeThe purpose of this paper is to elucidate if there is a loss in bond strength between galvanized steel used as reinforcement, and concrete of water‐to‐cement (w/c) ratio of 0.4 and 0.5, after both types of sample were cured for seven, 21 and 28 days in saturated calcium hydroxide solution, and without curing. The air permeability of the concrete was investigated at the interfacial zone.Design/methodology/approachStructural low‐carbon steel and galvanized steel were embedded in concrete samples, prepared with Portland cement type I and limestone (calcite 94‐97 percent) aggregates. The bond strength between the concrete and the reinforcing bars was measured by means of pull‐out tests.FindingsIn concrete of w/c=0.4 the bond for galvanized steel was 5.4±0.5 MPa, while the bond for black steel was 5.8±0.5 MPa, which is 7 percent higher than bond strength measured for samples with galvanized steel rebars. The bond strength for galvanized steel in concrete with a w/c ratio 0.5 was 5.5±0.6 MPa, which was 9 percent higher than the values obtained for black steel, which was 5.0±1 MPa. The total average bond strength of galvanized steel in concrete of w/c ratio 0.4 (5.4±0.5 MPa) and w/c ratio 0.5 (5.5±0.6 MPa) was very similar. They differed by only 2 percent. No decrease in the air permeability at the interfacial zone concrete/galvanized steel was found due to curing.Originality/valueThis research gives quantitative data on the behavior of galvanized steel used as reinforcing bars in concrete, prepared with limestone aggregates. The results might help to increase the reliability of galvanized reinforcing steel used in infrastructure exposed to very aggressive tropical humid marine environments.

Influence of Natural Bovine Enamel Roughness on Bond Strength after Etching

To determine and compare the longitudinal and transverse roughness parameters of the enamel surface of bovine teeth and evaluate the influence of these parameters on bond strength. Ninety bovine incisors were used. The surface roughness of enamel was measured with a profilometer. For each tooth, five readings were taken in the longitudinal plane and five were taken in the transverse plane of the long axis of the tooth in an area equal to the size of the bracket base. The metal brackets were bonded with Transbond XT, and bond strength was evaluated in a universal test machine. There was a statistical correlation (P < .01) between the longitudinal and transverse roughness measurements. There was no correlation between roughness measurements (longitudinal and transverse) and bond strength (P > .05), nor was there a correlation between total roughness (longitudinal Ra and transverse Ra) and bond strength. The Student's t-test showed that there was a statistically significant difference (P < .05) between longitudinal and transverse roughness. The transverse roughness is greater than the longitudinal roughness, there is a strong correlation between longitudinal and transverse roughness, and there is no correlation between enamel roughness and bond strength.

Theoretical analysis of the temperature and pressure dependences of the viscosity in supercooled liquids

In this paper, a method to analyze the temperature and pressure dependences of the viscosity or of the structural relaxation time in supercooled liquids is shown from the point of view of chemical bonding. The model used in this analysis is the Bond Strength–Coordination Number Fluctuation (BSCNF) model originally proposed by one of the authors. A theoretical relationship between the Vogel temperature T0 of the well-known Vogel-Flucher-Tammann (VFT) equation and our model parameters which contain some microscopic information on bonding connectivity among the structural units that form the melt has been obtained. Using the theoretical relationship, we analyzed the dynamics of two kinds of molecular glass forming liquids under pressure, (a) 4,4'-methylenebis(N,N-diglycidylaniline), and (b) BMPC: 1,1'-di(p-methoxyphenyl)cyclohexane. The result obtained suggests that by applying pressure in these materials, the intermolecular cooperativity is suppressed due to increases in the mean total bond strength and the fluctuations of the structural units.

Bonding Mechanisms in Cold Spraying: The Contributions of Metallurgical and Mechanical Components

The mechanism of bonding in cold spraying is still a matter of some debate. In this work, copper has been cold sprayed onto aluminium alloy substrates, the surfaces of which had been prepared in a variety of ways. The coating-substrate bonding was assessed via a novel intermetallic growth method along with adhesive pull-off testing, and related to the substrate preparation method. The bond strength has been rationalized in terms of a modified composite strength model, with two operative bonding mechanisms, namely (i) metallurgical bonding and (ii) mechanical interlocking of substrate material into the coating. In most cases, mechanical interlocking is able to account for a large proportion of the total bond strength, with metallurgical bonding only contributing significantly when the substrate had been polished and annealed prior to spraying. In addition, grit-blasting has been shown to significantly reduce the bond strength compared to other substrate preparation methods.

A model for the temperature dependence of the viscosity in Cu–As–Se system

The microscopic bonding behavior of amorphous Cu x (As 2Se 3) 1− x ( x = 0.00, 0.01, 0.05, 0.10 and 0.20) is studied from the point of view of the viscosity. The model used in this analysis describes the temperature dependence of the viscosity in terms of the mean bond strength E 0, the mean coordination number Z 0, and their fluctuations Δ E, Δ Z of the structural units that form the melt. The model reproduces quite well the temperature dependence of the viscosity of Cu x (As 2Se 3) 1− x observed experimentally. According to the theory, the fragility of the system increases as the fluctuation of the total bond strength increases. It is shown that the viscous flow is accompanied by the cooperative movements of the structural units and occurs by breaking selectively the weaker parts of the bonds between the structural units. This notion is related to the concept of Cooperatively Rearranging Region (CRR) in the theory of Adam–Gibbs. By analyzing the model, the fluctuation of the total bond strength in Cu–As–Se system is evaluated quantitatively, and the composition dependence of the fragility is discussed in terms of bond strength and the coordination number between the structural units. The analysis suggests that in the Cu x (As 2Se 3) 1− x system, there must be a strong composition dependence in the bond strength and a weak composition dependence in the fragility and coordination number fluctuation.

The Binding Properties of Terminal and Bridging Fluoride and of Aqua Ligands – a Semiempirical Vibronic Coupling and DFT Study of Mixed‐Ligand Manganese(III) Complexes

AbstractA combined vibronic coupling and angular overlap analysis of MIIIL6 complexes, supplemented by basic DFT calculations, is performed where the 3d cations are CrIII, FeIII or the Jahn‐Teller unstable MnIII cation, and the ligands L fluoride – in terminal (Ft) or in bridging (Fb) function – or OH2. Our approach is mostly semiempirical and based on a novel ligand strain model, which utilises available structural and spectroscopic data and mostly deals with mixed‐ligand MnIII complexes, containing simultaneously Ft, Fb and H2O. Surveying the great number of published structural data, some interesting results concerning the differing binding properties are derived. While the total bond covalency is similar for the three ligands, the total bond strength – and hence also the ionic bond increment – follows the sequence: Ft ≫ OH2 &gt; Fb. Partitioning the bond covalency into a part, which measures the ligand‐to‐metal charge flow (a), and an increment stemming from orbital (predominantly σ‐) overlap (b), one obtains: Ft ≫ Fb &gt; OH2 for (a) and the reverse sequence for (b).DFT model calculations on the [MIII(Ft)6]3− polyhedra in a solvent continuum were the basis for the elucidation of reliable ground state potential energy surfaces also for the further investigated complexes. The sometimes only very small energy difference between the involved three minima, generated via the interaction with the Jahn‐Teller active vibrational ϵg mode, led to various orthorhombic distortion conformers in the range between the tetragonal elongation and compression, depending on the strain magnitude imposed on the [Mn(Ft)6]3− parent polyhedron by a Ft‐by‐Fb (or OH2) substitution. It is further remarkable, that the average bond length of the Jahn‐Teller distorted octahedron varies significantly with the extent of the deformation and wether it is elongated or compressed – providing also computational evidence for the experimentally observed additional coupling to the totally symmetric α1g mode (Eg ⊗(ϵg + α1) vibronic interaction). The Jahn‐Teller stabilisation energy of the D4h‐elongated [MnIII(Ft)6]3− complex (absolute minimum) with respect to the regular octahedron can be defined as the difference between the non‐Jahn‐Teller restoring energy(≈ 0.3 eV) and the vibronic energy (≈ 0.65 eV). It is considerable (≈ −0.35 eV) in comparison to the stabilisation in regard to the compressed D4h‐conformer (≅ −0.075 eV).DFT was not successful in calculating d‐d transition energies within the 5Eg ground state of MnIII complexes containing the aqua ligand. Apparently, hydrogen bonds of varying strength to the higher‐sphere chemical environment and with significant energetic retroaction on the MnIII‐OH2 bonds exist, which cannot be correctly simulated by non‐sophisticated DFT.

An alternative way of characterising the bonding in compounds featuring main-group elements and with the potential for multiple bonding: on the dissociation of binary main-group hydrides.

Herein the bonding in compounds featuring main-group elements and with the potential for multiple bonding is studied theoretically by examination of their fragmentation into two fragments that still exhibit the same structure as they had in the molecule prior to dissociation. The fragments were calculated both in their electronic ground state and in an excited electronic state, in which the number of unpaired electrons is equal to the maximal number of bonds in the compounds before dissociation. The energies of the fragmentation processes (DeltaE(frag)) can be more directly linked to the bond strengths than the dissociation energies (DeltaE(diss)), because of the absence of any secondary effects like relaxation of the electronic state or of the geometry of the fragments. These relaxation energies of the fragments (DeltaE(frag)) are also studied herein. The energies derived in this work allow for an accurate comparison of the bonding properties in main-group-element hydrides. The trends of the fragmentation and relaxation energies are discussed in detail. It will be shown that the relaxation energies allow for a classification of the bonds ("classical" sigma and pi bonds or donor-acceptor interactions), while the fragmentation energies are good quantitative measures for the total bond strength. Similar calculations are on the way to explore the bonding in systems in which the hydrogen atoms are replaced by organic groups or halogen atoms.

A model for the fragility of the melts

The concept of fragility has been used widely to characterize the temperature dependence of the viscosity of glass forming materials. However, the physical background that determines the degree of fragility is still not well understood. In the present study an expression for the fragility is derived based on a simple model of the melt. According to the model, the fragility is determined by the relaxation of structural units that form the melt, and is described in terms of the bond strength (E 0), coordination number (Z 0), and their fluctuations (ΔE and ΔZ). It is shown that a strong system is characterized by large value of total bond strength (Z 0 E 0) and small value of its fluctuation ((ΔZ)2(ΔE)2). On the other hand, a fragile system is characterized by small value of total bond strength and large value of its fluctuation.

Application Study on Ceria Based Thermal Barrier Coatings

en

Alloying effects on the electronic structure of ZrMn 2 intermetallic hydride

The electronic structures of ZrMn 2 intermetallic hydride containing a variety of alloying elements are investigated by the DV-X α cluster method. It is found that hydrogen atom makes a strong chemical bond with Mn atoms rather than Zr atoms in pure ZrMn 2 hydride. The substitution of alloying elements for Mn atoms scarcely modifies the total bond strength between hydrogen and metal atoms, despite the fact that hydrogen absorption and desorption characteristics change significantly with alloying elements. On the contrary, both the Mn–Mn and the Zr–Mn interactions are greatly affected by alloying. It is shown that the ratio of the Zr–Mn bond order to the Mn–Mn bond order in a small tetrahedron containing a hydrogen atom, correlates well with experimental data of the equilibrium hydrogen pressure of alloyed ZrMn 2.

Bond strength versus dentine structure: A modelling approach

Bond strengths of a hypothetical hydrophilic dentine-bonding agent were calculated as a function of dentine depth and resin strength to evaluate the importance of several variables in a simple model. The tested hypothesis was that the total bond strength was the sum of the strengths of resin tags, hybrid layer and surface adhesion. Each of these three variables has a range of values that can influence its relative contribution. The resulting calculations indicate the potential for higher bond strengths to deep dentine than to superficial dentine in non-vital dentine and the importance of resin strength in the development of strong bonds. Comparison of the calculated bonds with published values indicated that they were within the same order of magnitude. Such theoretical modelling of dentine bonding can identify the relative importance of variables involved in the substrate, resins and surface adhesion.