Changes in bone’s micromechanical properties caused by fatigue fracture

The role of bone fatigue damage at the nanostructural level, and its effect on fatigue properties is an understudied and important subject. In this study, nanoindentation was used to probe the micro-mechanical properties of bovine tibiae subjected to fatigue loading in four-point bending. Indentation tests were conducted in the same 30 μm?×?120 μm region before fatigue loading and after loading to fracture. Using an optical microscope and scanning electron microscope, the morphology of the initial residual indentation before fatigue loading appeared the same as that after loading to fracture. The mechanical properties calculated using nanoindentation were reduced modulus and hardness, the time constant based on creep, long-term creep viscosity and the dissipated work. Differences of each parameter before loading and post fracture were examined using paired t-tests. The results show that the reduced modulus decreased significantly (p?=?9.47?×?10^–3) by 7.62–15.16% after fracture whereas the time constant of creep increased slightly (p?=?0.049) by 2.81–5.41%. There was no clear change in hardness or dissipated work with fatigue loading. Fatigue loading has the largest effect on bone’s reduced modulus compared to all other mechanical properties.

     

The strengthening effect caused by an elastic contrast��part II: stratification by a thin stiff layer

To quantify the gain in strength of a layered heterogeneous structure caused by the elastic contrast between the layers, especially if no crack deflection is observed at the interface, two original mechanisms baptized ??step-over?? and ??jump-through?? were proposed in Part I. They addressed the ability of a crack to pass through an interface and were applied to a bimaterial structure; whereas part II is dedicated to a homogeneous beam embedding a thin stiff film. The asymptotic expansions differ significantly since the small parameter is now the layer thickness. Unlike the first part where it was difficult to evidence the gain in toughness due to the superposition of two effects: a simultaneous increase in stiffness and in toughness, here it is possible to characterize the strength enhancement in using a single parameter. A discussion of the possibility to repeat the effect by multiplying the thin films is presented at the end.     

Anomalous celestial polarization caused by forest fire smoke: why do some insects become visually disoriented under smoky skies?

The effects of forest fire smoke on sky polarization and animal orientation are practically unknown. Using full-sky imaging polarimetry, we therefore measured the celestial polarization pattern under a smoky sky in Fairbanks, Alaska, during the forest fire season in August 2005. It is quantitatively documented here that the celestial polarization, a sky attribute that is necessary for orientation of many polarization-sensitive animal species, above Fairbanks on 17 August 2005 was in several aspects anomalous due to the forest fire smoke: (i) The pattern of the degree of linear polarization p of the reddish smoky sky differed considerably from that of the corresponding clear blue sky. (ii) Due to the smoke, p of skylight was drastically reduced (p(max)相似文献   

The strengthening effect caused by an elastic contrast��part I: the bimaterial case

The final aim of the two parts of this study is to quantify the gain in strength of a layered heterogeneous structure caused by the elastic contrast between the layers, especially if no crack deflection is observed at the interface. In part I, the analysis focus on an example, the 3 point-bending of a bimaterial made of a compliant and a stiff layer; whereas part II is dedicated to the 3-point bending of a homogeneous beam embedding a thin stiff film. Baptized ??step-over?? and ??jump-through??, two original mechanisms of crack crossing the interface are proposed herein. They rely on a coupled criterion involving both energy requirement and stress condition. It is established from asymptotic expansions and the theory of singularities. This criterion is able to respond to the paradox posed by the traditional tools of brittle fracture mechanics which might carelessly conclude to a quasi infinite strength enhancement. The subtitle of this first part might be: can a crack pass through an interface?     

Comparison of the bone modeling effects caused by curved and straight nickel–titanium intramedullary nails

Nitinol (NiTi) shape memory metal alloy makes it possible to prepare functional implants. A curved intramedullary NiTi nail has been shown to cause bending of the bone, bone thickening, increase in cortical area, and reduction in bone longitudinal growth. The purpose of the present study was to find out whether these changes are caused by the bending force of the curved nail or by the intramedullary nailing itself. Pre-shaped intramedullary NiTi nails were implanted in the cooled martensitic form into the medullary cavity of the right femur in 12 rats, where they started to restore their austenitic form, causing a bending force. Straight nails were used as controls in another 12 rats. After 12 weeks, the operated femurs were compared with their non-operated contralateral counterparts and the differences were compared between the groups. Anteroposterior radiographs demonstrated bone bowing only in the curved nail group. Retardation of longitudinal growth was observed in both groups, showing that the growth effect seems to be due to the intramedullary nailing itself. Increase in bone cross-sectional area and cortical thickness were found in both groups. However, this increase was more evident with the curved nail, indicating that the bending force of the functional nail seems to induce these changes.     

Is science driven by principal investigators?

Scientometrics - In this paper we consider the question what is the scientific and career performance of principal investigators (PI’s) of publicly funded research projects compared to...     

The impact of a 360° virtual tour on the reduction of psychological stress caused by COVID-19

The continuous spread of the COVID-19 pandemic is causing people to feel anxiety and stress. This study constructs a four-layer research model to examine how a 360° virtual tour can reduce people's psychological stress through two types of presence (the sense of presence and telepresence) and affective-motivational states (enjoyment and involvement) in this extraordinary period of the COVID-19 pandemic. In order to test the moderating effect of involvement, partial least squares (PLS) analysis is employed to analyse valid data collected from 235 individuals. The results of this study indicate that telepresence has a higher impact in generating affective-motivational states than the sense of presence. Among the factors, enjoyment shows the highest effect on satisfaction with the 360° virtual tour experience and stress reduction; involvement moderates the effect of telepresence on satisfaction with the 360° virtual tour experience. This study also contributes to virtual reality research by distinguishing the concepts of ‘sense of presence’ and ‘telepresence’ as well as demonstrating the mechanisms whereby virtual reality technology influences people's psychological well-being. Timely recommendations are provided for people in order to reduce psychological stress during and after COVID-19 pandemic.     

Copper-oxide whisker growth on tin–copper alloy coatings caused by the corrosion of Cu6Sn5 intermetallics

This paper reports the effect of corrosion caused by high temperature and humidity on pure tin and tin–copper alloy coatings. A new phenomenon was observed; the development of copper-oxide whiskers on tin–copper alloys plated on copper substrates (1–5 % copper content stored at 105 °C/100 % relative humidity). The copper-oxide whiskers showed similar growth properties to tin whiskers. We have made a model to understand the development of copper-oxide whiskers. Localized corrosion of the tin coating reaches the Cu₆Sn₅ intermetallic layer, and copper oxide accumulates after the corrosion of Cu₆Sn₅. The dilating SnO _x compresses and extrudes out the copper oxide in a whisker form.     

Orientation and temperature dependence of superelasticity caused by reversible γ-α′ martensitic transformations in FeNiCoAlTa single crystals

Reversible thermoelastic γ-α′ martensite transformations (MTs) have been studied in Fe-28%Ni-17%Co-11.5%Al-2.5%Ta (at. %) single crystals under cooling/heating and loading conditions. It is established that the precipitation of dispersed γ′ phase particles with an average size of d ≤ 5 nm leads to thermoelastic γ-α′ MTs with a small temperature hysteresis (ΔT = 20 K). The [001] oriented crystals favor the attaining of maximum superelasticity (SE) ɛ_SE = 6.8%, minimum mechanical hysteresis Δσ = 130 MPa, and large SE temperature interval ΔT _SE = 130 K. In contrast, in the [111] oriented crystals, small values of ɛ_SE = 2.0%, high values of Δσ = 350–400 MPa and narrow SE interval ΔT _SE = 55 K are found.     

Mn²+-bonded reduced graphene oxide with strong radiative recombination in broad visible range caused by resonant energy transfer

The photoluminescence (PL) characteristics of Mn(2+)-bonded reduced graphene oxide (rGO) are studied in details. The Mn(2+)-bonded rGO is synthesized using MnO(2)-decorated GO as the intermediate products and ideal tunable PL is obtained by enhancing the long-wavelength (450-550 nm) emission. The PL spectra excited by different wavelengths are analyzed to elucidate the mechanism, and the resonant energy transfer between Mn(2+) and sp(2) clusters of the rGO appears to be responsible for the enhanced long-wavelength emission. To examine the effect of Mn(2+) on the long-wavelength emission from the Mn(2+)-bonded rGO, the PL characteristics of Mn(2+)-bonded rGO with smaller Mn concentrations are studied and weaker emission is observed. Our theoretical calculation corroborates the experimental results.     

An Efficient SQUID NDE Defect Detection Approach by?Using?an?Adaptive?Finite-Element?Modeling

Incorporating the finite-element method for the modeling of the SQUID NDE response to a predefined defect pattern, an adaptive algorithm has been developed for the reconstruction of unknown defects using an optimization algorithm for updating of the forward problem. The defect reconstruction algorithm starts with an initial estimation for the defect pattern. Then the forward problem is solved and the obtained field pattern is compared with the measured signal from the SQUID NDE system. The result is used by an optimization algorithm to update the defect structure to be incorporated in the FEM forward problem for the next iteration. Since the mentioned model based inverse algorithm normally consumes a lot of computational resources, the number of iterations plays an important role in the determination of the total response convergence time. Consequently, different optimization algorithms have been applied and their performances are compared. In this work by incorporating an efficient forward model and using the stochastic and deterministic optimization algorithms for defect updating we have investigated their performance on the inversion of the SQUID NDE signal and also their ability to defect reconstruction in the noisy environment.     

Implementation of Molecular Transistor Electrodes by?Electromigration

Gaps with a size of less than 5 nm have been fabricated in 15-nm-thick and 200-nm-wide gold strips deposited on sapphire substrates. Preparation conditions providing a sufficient adhesion of such electrodes as well as the parameters for the electromigration process used to fabricate the gaps have been found which allow a successful gap implementation. Such gaps transform gold strips to the source-drain electrodes of planar single electron transistors based on nanoparticles or molecules.     

On the Structural Transition Driven by Band Nesting in?1111?Pnictides

The lattice critical response in REFeAsO (RE=Pr, Nd and Sm) oxypnictides near the orthorhombic-to-tetrahedral structural phase transition is studied using ultra-high-resolution X-ray diffraction in the temperature range 4 to 250 K. The critical exponent of the structural phase transition ?? is found to decrease with decreasing RE size. The ?? values determined to be 0.212, 0.209 and 0.194, respectively, for PrOFeAs, NdOFeAs and SmOFeAs. Temperature hysteresis is observed for all the REFeAsO, with ??T being of the order of 2 to 3 K. The results are discussed in the frame of Fermi surface nesting induced structural transition in the pnictides.     

Can breath isoprene be measured by ozone chemiluminescence?

Isoprene, involved in the biosynthetic pathway to cholesterol, is the prevalent hydrocarbon in breath. Breath isoprene measurement is of great interest as a measure of basal cholesterol production rate. We investigated the merits and pitfalls of isoprene measurement via its chemiluminescence (CL) reaction with ozone. For many subjects, apparent concentrations measured are higher than those obtained by a gas chromatography (GC) reference method that can be traced to ozone-induced CL with simultaneously present lower olefins and sulfur compounds. A warm column preconcentration method eliminates the lower olefins and greatly improves sensitivity while a silver-form, ion-exchange resin can remove the sulfur gases. The breath sample is captured on a miniature synthetic carbon sorbent column maintained at 55 degrees C, under which conditions ethylene, propylene, and water vapor are not significantly captured while the preconcentration process greatly improves the limit of detection for isoprene to 0.6 ppbv (S/N=3). The captured isoprene is released by heating the column to 150 degrees C. Breath samples from different subjects were collected both before and after meals and analyzed in a double-blind fashion in two laboratories, with the second laboratory performing quantitation by cryofocusing GC-flame ionization detection with parallel measurement by mass spectrometry to provide identity confirmation. For all individuals studied, the CL and the GC results agreed when both warm column preconcentration and passage through Ag+-form cation-exchange resin, which removes divalent sulfur gases, were implemented prior to CL measurement. The intensity of CL from the reaction with ozone can be much higher for some sulfur gases than for isoprene. Even though present at lower concentrations than isoprene, unless removed prior to CL measurement, for some individuals sulfur gases can cause unacceptably large (up to 500%) errors, making the sulfur gas removal step critical.