Exact solution of cilia induced flow of a Jeffrey fluid in an inclined tube.

The present study investigated the cilia induced flow of MHD Jeffrey fluid through an inclined tube. This study is carried out under the assumptions of long wavelength and low Reynolds number approximations. Exact solutions for the velocity profile, pressure rise, pressure gradient, volume flow rate and stream function are obtained. Effects of pertinent physical parameters on the computational results are presented graphically.

Characterizing and identifying incipient carious lesions in dental enamel using micro-Raman spectroscopy.

Early detection of dental caries is vital if improved patient outcomes are to be achieved by reversal of the demineralization process. Current techniques used by dentists for identifying carious lesions are effective in identifying more advanced lesions, but do not have sufficient sensitivity and specificity to detect them at the earliest stages. This study focused on characterizing the growth of incipient carious lesions in vitro using micro-Raman spectroscopy. The incipient carious lesions were grown on the buccal faces of human molars by controlled exposure to lactic acid. Lesions were cross-sectioned to expose the subsurface body of the lesion and then examined using micro-Raman spectroscopy. The intensity of the phosphate peaks in the Raman spectra was found to differ significantly between healthy enamel and the demineralized region of the lesions. The sensitivity of the phosphate peaks to the degree of demineralization was observed by taking a series of spectra over the cross section of the lesions. This revealed that the body of the lesion is highly demineralized, but in a narrow surface region (up to 10 µm) there is little demineralization. All the phosphate peaks were found to be sensitive to the degree of demineralization; however, changes in the intensity of the pronounced phosphate peak at 961 cm(-1) offer the most promise for identifying lesions. The results indicate that micro-Raman spectroscopy has both the sensitivity and selectivity to identify incipient carious lesions, but the presence of a surface layer with a relatively high mineral content could complicate the analysis.

Hierarchies of damage induced loss of mechanical properties in calcified bone after in vivo fatigue loading of rat ulnae.

During fatigue loading of whole bone, damage to bone tissue accumulates, coalesces and leads to fractures. Whether damage affects tissue material properties similarly at the nanoscale (less than 1 µm), microscale (less than 1 mm), and whole bone scale has not been fully evaluated. Therefore, in this study, we examine scale-dependent loss of calcified tissue material properties in rat ulnae, after fatigue loading of rat forearms using the forearm compression model. In vivo fatigue loading was conducted on the right forearms until a displacement end-point was reached. The non-fatigued left forearms served as contralateral controls. Subsequently, three-point bending tests to failure on excised ulnae demonstrated a 41% and 49% reduction in the stiffness and ultimate strength as compared to contralateral control ulnae, respectively. Depth-sensing microindentation demonstrated an average decrease in material properties, such as elastic modulus and hardness, of 28% and 29% respectively. Nanoindentation measured elastic modulus and hardness were reduced by 26% and 29% in damaged bone relative to contralateral controls, respectively. The increased loss of whole bone material properties compared to tissue material properties measured using indentation is mainly attributed to the presence of a macrocrack located in the medial compressive region at the site of peak strains. The similar magnitude of changes in material properties by microindentation and nanoindentation is attributed to damage that may originate at an even smaller scale, as inferred from 10% differences in connectivity of osteocyte canaliculi in damaged bone.

Effect of osteocalcin deficiency on the nanomechanics and chemistry of mouse bones.

In healthy bone there is a balance between bone resorption and formation. When an imbalance occurs there is an overall loss of bone mass leading to an increased risk of fracture. The deterioration is typically accompanied by changes in the non-collagenous proteins in the bone. Osteocalcin (OC) is the most abundant noncollageneous bone matrix protein and it is believed to play a role in bone formation and resorption. Nanoindentation and Raman microspectroscopy have been used to correlate the mechanical and chemical properties of cortical bone from femora of OC -/- (osteocalcin deficient) mice and their wild-type controls (OC +/+). There are significant intra-bone variations in mechanics and crystallinity especially in the mid-cortical section for OC -/- mice compared to OC +/+ mice. Type-B carbonate substitution decreased significantly in the absence of osteocalcin and this appears to affect the hardness more than the elasticity. The results suggest that OC plays a role in the growth of apatite crystals in bone by increasing the degree of carbonate substitutions. The addition of these defects to the apatite's crystal lattice has little effect on elasticity, but does appear to reduce the bone's hardness.

A note on plane wave diffraction by a perfectly conducting strip in a homogeneous bi-isotropic medium.

We studied the problem of diffraction of an electromagnetic plane wave by a perfectly conducting finite strip in a homogeneous bi-isotropic medium and obtained some improved results which were presented both mathematically and graphically. The problem was solved by using the Wiener-Hopf technique and Fourier transform. The scattered field in the far zone was determined by the method of steepest decent. The significance of present analysis was that it recovered the results when a strip was widened into a half plane.

The effect of prism orientation on the indentation testing of human molar enamel.

Recent nanoindentation studies have demonstrated that the hardness and Young's modulus of human molar enamel decreases by more than 50% on moving from the occlusal surface to the dentine-enamel junction on cross-sectional samples. Possible sources of these variations are changes in local chemistry, microstructure, and prism orientation. This study investigates the latter source by performing nanoindentation tests at two different orientations relative to the hydroxyapatite prisms: parallel and perpendicular. A single sample volume was tested in order to maintain a constant chemistry and microstructure. The resulting data show very small differences between the two orientations for both hardness and Young's modulus. The 1.5-3.0% difference is significantly less than the standard deviations found within the data set. Thus, the variations in hardness and Young's modulus on cross-sectional samples of human molar are attributed to changes in local chemistry (varying levels of mineralization, organic matter, and water content) and changes in microstructure (varying volume fractions of inorganic crystals and organic matrix). The impact of prism orientation on mechanical properties measured at this scale by nanoindentation appears to be minimal.

Nanomechanical and chemical characterization of incipient in vitro carious lesions in human dental enamel.

OBJECTIVE: The research was designed to examine the growth of in vitro carious lesions in dental enamel using nanoindentation and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). This was intended to give maps of mechanical properties and chemistry over the cross-section of the lesions. METHODS: Incipient carious lesions were grown on the buccal faces of 20 human premolars by exposure to acid for 3, 5, 7 or 14 days. The lesions were then cut in cross-section normal to the exposed surface. The lesions' cross-sections were then examined using nanoindentation and TOF-SIMS. RESULTS: The earliest lesions (3 days of acid exposure) showed little evidence of lesion growth, but the 5, 7 and 14 days of exposure all gave lesions with a weak, demineralized interior, but a stronger, less demineralized surface zone. The thickness of the surface zone was found to diminish with the length of exposure to acid, but it was still present even after 14 days of exposure. CONCLUSION: The results indicate that carious lesions develop subsurface and that the surface zone forms by a coupled diffusion process. Mechanically the lesion has a strong surface layer, but a very weak interior which makes the lesion vulnerable to mechanical loading. However, the presence of a surface zone that retains a high mineral content and is mechanically strong suggests that lesion development can be arrested and possibly reversed even when the lesions are relatively mature.

Nanoindentation mapping of the mechanical properties of human molar tooth enamel.

The mechanical behavior of dental enamel has been the subject of many investigations. Initial studies assumed that it was a more or less homogeneous material with uniform mechanical properties. Now it is generally recognized that the mechanical response of enamel depends upon location, chemical composition, and prism orientation. This study used nanoindentation to map out the properties of dental enamel over the axial cross-section of a maxillary second molar (M(2)). Local variations in mechanical characteristics were correlated with changes in chemical content and microstructure across the entire depth and span of a sample. Microprobe techniques were used to examine changes in chemical composition and scanning electron microscopy was used to examine the microstructure. The range of hardness (H) and Young's modulus (E) observed over an individual tooth was found to be far greater than previously reported. At the enamel surface H>6GPa and E>115GPa, while at the enamel-dentine junction H<3GPa and E<70GPa. These variations corresponded to the changes in chemistry, microstructure, and prism alignment but showed the strongest correlations with changes in the average chemistry of enamel. For example, the concentrations of the constituents of hydroxyapatite (P(2)O(5) and CaO) were highest at the hard occlusal surface and decreased on moving toward the softer enamel-dentine junction. Na(2)O and MgO showed the opposite trend. The mechanical properties of the enamel were also found to differ from the lingual to the buccal side of the molar. At the occlusal surface the enamel was harder and stiffer on the lingual side than on the buccal side. The interior enamel, however, was softer and more compliant on the lingual than on the buccal side, a variation that also correlated with differences in average chemistry and might be related to differences in function.

[Reconstitution of the Gypsy family using data from three communes]. / Vyvoj romskej rodiny na priklade troch spisskych obci.

PIP: The extent to which the Gypsy population of Slovakia has experienced demographic transition is explored. Data from three communal registers are used to reconstruct their family history from the late nineteenth century to the present. Particular demographic characteristics of the Gypsy population are also discussed. (SUMMARY IN ENG AND RUS)^ieng