Influence Of Mechanical Strain Research Articles

Direct Observation of Band-Gap Closure for a Semiconducting Carbon Nanotube in a Large Parallel Magnetic Field

We have investigated the magnetoconductance of semiconducting carbon nanotubes (CNTs) in pulsed, parallel magnetic fields up to 60T, and report the direct observation of the predicted band-gap closure and the reopening of the gap under variation of the applied magnetic field. We also highlight the important influence of mechanical strain on the magnetoconductance of the CNTs.

Influence of mechanical strain on the electrical properties of flexible organic thin-film transistors

In this study, we systematically investigated the bending effect on the electrical properties of flexible organic thin-film transistors (OTFTs) fabricated on stainless steel substrates. We found that the compressive strain resulted in an increased mobility, while the tensile strain degraded the electrical performance. We further used a transfer line method to extract the channel and parasitic resistances under either compressive or tensile strain. The results indicated that the parasitic resistance increased apparently under the tensile bending condition, which probably could be attributed to the damage of the source/drain contacts. Additionally, we deduced that mechanical strains influence the energy barrier height between the grains of pentacene thin films, thereby resulting in the variation of channel resistances. Overall, the flexible OTFTs fabricated on the metal foils exhibited high mechanical flexibility and stability.

Influence of Mechanical Strain on the Electrochemical Lithiation of Aluminum-Based Electrode Materials

While an Al-Li alloy is expected to be useful as an active material for a negative electrode in a Li battery, the electrochemical lithiation of pure Al metal is known to be quite difficult. In this work, we sought to clarify why an Al electrode hardly absorbs Li from a pure Al state, from the viewpoint of elasticity theory and thermodynamics. We consider two cases: (i) an AlLi compound with elastic strain due to volume expansion is formed in the Al matrix, and (ii) Li ions are absorbed into an Al electrode that has been pre-strained by rolling. These strain-energy effects are discussed with the aid of a chemical-potential diagram and the Gibbs-Duhem equation.

The influence of mechanical strain on the optical properties of spherical gold nanoparticles

Abstract We utilize classical Mie scattering theory to investigate the effects of tensile and compressive mechanical strain on both the far field (absorption, scattering and extinction efficiencies) and near field (surface enhanced Raman scattering) optical properties of spherical gold nanoparticles with diameters ranging from 10 to 100 nm. By accounting for the strain effects on both the ionic core (bound) and conduction (free) electrons through appropriate modifications of the bulk dielectric functions, we find that gold nanoparticles are relatively sensitive to the effects of mechanical strain due to the fact that the plasmon resonance wavelength for spherical gold particles, which occurs around λ = 520 nm , is nearly coincident with the interband transitions of the core electrons. Specifically, we find that tensile strain leads to significant enhancements ranging from 60% to 120% in the far field optical efficiencies, while compressive strain leads to similar decreases, and that the plasmon resonance wavelength can be red or blueshifted up to 100 nm due to the applied strain. Finally, we find that tensile strain also strongly enhances the local electric ( E )-field at the surface of the nanoparticles, which is of considerable interest for surface-enhanced Raman scattering applications; 5% tensile strain is found to enhance the | E | 4 intensity by 63%. The present results demonstrate the potential of mechanical strain, and specifically that of tensile mechanical strain in enhancing and tailoring the optical properties of gold nanoparticles.

Influence of mechanical strain on magnetic characteristics of spin valves

Giant magnetoresistance (GMR) of Co and Fe-Co based e-beam evaporated spin valves with Cu and Au spacers was studied. The effect of strain on samples, which is detrimental in standard GMR sensors, was measured in a bending configuration. The different dependences of coercivity Hc and magnetic field Hip in the point of inflection of MR loops vs. strain were found. For sample with Co/Au/Co core, Hc, Hip increase with increasing compressive stress, whereas for sample with FeCo/Cu/Co core they increase with tensile stress. The highest relative change of MR ratio vs. bending in the strain interval ± 300 × 10−6 is 1–2 % of the basic magnetoresistance and, practically, it does not influence the SV output.

Effects of 17β-estradiol on growth and apoptosis in human vascular endothelial cells: Influence of mechanical strain and tumor necrosis factor-α

Vascular endothelial cell (EC) integrity is key to arterial health; endothelial dysfunction is linked to atherogenesis. Atherosclerosis shows a male preponderance, possibly related to the protective effect of estrogens in women. This study examined the effect of estrogens on growth, apoptosis and adhesion molecule expression in cultured human EC. The effects of 17β-estradiol (E2) were studied in human umbilical vein endothelial cells (HUVEC) under normal culture conditions, and following exposure to cyclic mechanical strain or tumor necrosis factor α (TNFα). E2 enhanced HUVEC growth in serum-enriched media, in a concentration-dependent manner. This up-regulation of EC growth by E2 was associated with an increase in telomerase activity, assessed by PCR-based TRAP analysis. Cyclic strain enhanced [ 3H]-thymidine incorporation into DNA, and increased activation of mitogen-activated protein (MAP) kinase ERK1/2 and expression of early growth genes (Egr-1 and Sp-1); E2 attenuated the strain-induced ERK1/2 activation but not the early growth gene expression or DNA synthesis. TNFα (20 ng/mL) induced apoptosis in HUVEC, causing a decrease in DNA synthesis, increase in floating and Annexin-V-stained cell numbers, and morphological changes. TNFα also upregulated ERK1/2 activity and expression of adhesion molecules (ICAM-1, VCAM-1 and E-selectin). E2 significantly attenuated the effects of TNFα on ERK1/2 activity, apoptosis, and E-selectin expression in the cells. Thus, estradiol enhances growth and reduces TNFα-induced apoptosis in EC; enhanced EC growth may be mediated via upregulation of telomerase activity. These effects are possible cellular mechanisms underlying female gender-associated cardiovascular protection.

The influence of mechanical strain on adult rat marrow stromal cell dynamics

The combination of a β-tricalcium phosphate (βTCP) block with a scaffold-free chondrocyte sheet formed by the centrifugation of chondrocytes in a well was investigated with the aim of constructing an osteochondral-like structure.Human and porcine articular cartilage chondrocytes were respectively centrifuged in a 96-well plate or cell culture insert (0.32 cm2) that was set in a 24-well plate, cultivated in the respective vessel for 3 weeks, and the cell sheets were harvested. In some cases, a cylindrical βTCP block (diameter 5 mm, height 3 mm) was placed on the sheet on days 1–7. The sheet size, cell number, and sulfated glycosaminoglycan accumulation were determined.The use of a 96-well plate for not suspension but adhesion culture and the initial centrifugation of a well containing cells were crucial to obtaining a uniformly thick cell sheet. The glycosaminoglycan density of the harvested cell sheet was comparable to that of the pellet culture. An inoculum cell number of more than 31 × 105 cells tended to result in a curved cell sheet. Culture involving 18.6 × 105 cells and the 96-well plate for adhesion culture showed no curving of the cell sheet (thickness of 0.85 mm), and these were found to be the best of the culture conditions tested. The timing of the addition of a βTCP block to the cell sheet (1–7 days) markedly affected the balance between the thickness of cell sheet parts on and in the βTCP block.Centrifugation and subsequent cultivation of chondrocytes (18.6 × 105 cells) in a 96-well plate for adhesion culture led to the production of a scaffold-free cartilage-like cell sheet with a thickness of 0.85 mm. A combined osteochondral-like structure was produced by putting a βTCP block on the cell sheet. The thickness of the cell sheet on the βTCP block and the binding strength between the cell sheet and the βTCP block could be optimized by adjusting the inoculum cell number and timing of βTCP block addition.

Superconducting and mechanical performance and the strain effects of a multifilamentaryMgB2/Ni tape

Superconducting and mechanical performance and the straineffect, the influence of mechanical strain on the critical current(Ic), are investigated for a commercially availableMgB2 multifilamentary tape. The conductor was made through the ex situroute and has 14 filaments in nickel matrix with copper stabilizer.Ic was measured as a function of magnetic field(B) at 4.2, 15, 20, and 25 K and we determined the irreversibility fields(Birr) usingIc–B curves at eachtemperature. Ic, measured as a function of field angle at 4.2 K and 4 T, shows an anisotropic behaviour. We also measuredIc as a function of temperature in 0–5 T. The stress–strain relation was testedat 296 and 113 K. The strain effect was examined in magnetic fields at 4.2,15, and 20 K using a U-shape rig made of stainless steel (SUS304). TheIc–strain relation is linear and reversible in the window of external strain between−0.5% (compression) and 0.5% (tension). With increasing strain,large and irreversible degradation occurs after the maximum ofIc (Icm) at 0.57% tension.Although d (Ic/Icm)/d (strain), theslope of the linear Ic–strain relation in the reversible regime, depends on both temperature and magnetic field, the relationsbetween d (Ic/Icm)/d (strain) and B/Birr fall on a universal line independently of temperature.

Influence of cyclic mechanical strain and heat of human tendon fibroblasts on HSP-72

Heat shock protein 72 (HSP-72) is a member of a superfamily of different proteins that are synthesized as a cytoprotective response following cellular stress. Mechanical strain is an important component in ligament and tendon healing. Up to the present point of time, the influence of mechanical strain on the expression of HSP-72 is unknown. Tendon fibroblasts from the patellar tendons of nine individuals were isolated and amplified in vitro. First, the effect of 15 or 60 min of heat exposition was studied immunohistochemically and by Western blotting. In a second experiment, the effects of 15 and 60 min of cyclic longitudinal stretching were investigated. Samples were taken after 2, 4 and 8 h. The heat exposition experiments indicate that HSP-72 accumulates in the nucleus and that there is a transient upregulation. This effect is more prominent after 60 min of heat exposure. The same reaction was found after stretching stimulation, however, to a lesser extent. There was a transient up regulation of HSP-72 after short-term stretching and a biphasic increase after 60 min of stretching. Upregulation of HSP-72 by heat and mechanical stress is a response in human fibroblasts which involves a nuclear translocation. The response differs with regard to the time points beyond 2 h after the application of either stress.

Critical current of magnesium diboride/stainless steel composite tapes under tensile or compressive strains

We investigate the influence of mechanical strain on the critical current (Ic) for magnesium diboride/stainless steel (SUS316) superconducting tapes. The tensile axial strain along the tape length is successfully induced in the sample by using a U-shaped holder made of stainless steel (SUS304). Two samples are examined at 4.2 K and 5 T (B is applied perpendicular to the tape surface). The Ic–strain relation can be divided into two regions. Rapid and large degradation occurs at a strain exceeding ∼0.5%. On the other hand, Ic change is reversible against strain change between −0.4% (compressive strain) and 0.4%. Ic increases and decreases with increasing and decreasing external strain in this region, respectively. The critical temperature (Tc) also changes with the change in the external strain; Tc increases with increasing external strain. The reversible change in Ic originates in the change of Tc.

Systemic regulation of distraction osteogenesis: a cascade of biochemical factors.

This study investigates the systemic biochemical regulation of fracture healing in distraction osteogenesis compared with rigid osteotomy in a prospective in vivo study in humans. To further clarify the influence of mechanical strain on the regulation of bone formation, bone growth factors (insulin-like growth factor [IGF] I, IGF binding protein [IGFBP] 3, transforming growth factor [TGF] beta1, and basic FGF [bFGF]), bone matrix degrading enzymes (matrix-metalloproteinases [MMPs] 1, 2, and 3), human growth hormone (hGH), and bone formation markers (ALP, bone-specific ALP [BAP], and osteocalcin [OC]) have been analyzed in serum samples from 10 patients in each group pre- and postoperatively. In the distraction group, a significant postoperative increase in MMP-1, bFGF, ALP, and BAP could be observed during the lengthening and the consolidation period when compared with the baseline levels. Osteotomy fracture healing without the traction stimulus failed to induce a corresponding increase in these factors. In addition, comparison of both groups revealed a significantly higher increase in TGF-beta1, IGF-I, IGFBP-3, and hGH in the lengthening group during the distraction period, indicating key regulatory functions in mechanotransduction. The time courses of changes in MMP-1, bone growth factors (TGF-beta1 and bFGF), and hGH, respectively, correlated significantly during the lengthening phase, indicating common regulatory pathways for these factors in distraction osteogenesis. Significant correlation between the osteoblastic marker BAP, TGF-beta1, and bFGF suggests strain-activated osteoblastic cells as a major source of systemically increased bone growth factors during callus distraction. The systemic increase in bFGF and MMP-1 might reflect an increased local stimulation of angiogenesis during distraction osteogenesis.

Highly sensitive strain sensors based on magnetic tunneling junctions

Micrometer-sized highly sensitive strain sensors are presented. The sensors are based on magnetic tunneling junctions (MTJs) incorporating magnetostrictive free layers. The influence of mechanical strain upon the free layer is explained by a model taking into account the total free energy of the sensing layer. Those MTJ devices prepared in situ with magnetostrictive Fe50Co50 layers exhibit a tunneling magnetoresistance (TMR) ratio of 48%. The changes in strain Δε on the order of 0.4 parts per thousand (‰) result in resistance changes of 24%, which in turn leads to gauge factors [(ΔR/R)/Δε] on the order of 600, whereas gauge factors of 2–4 are typical for metal based, and 40–180 for piezoresistive semiconductor strain gauges.

Temperature and magnetic field dependence of the critical current density for a mass-produced Nb/sub 3/Al multifilamentary strand fabricated by a jelly-roll method [for ITER

JAERI has been developing jelly-roll processed multifilamentary Nb/sub 3/Al-Cu strands for the toroidal field (TF) coils of fusion tokamak machines since 1986, in cooperation with Sumitomo Electric Industries. One ton of mass-produced strands were successfully manufactured for the 13 T-46 kA Nb/sub 3/ Al insert which will be tested in the ITER Central Solenoid model coil. The critical current of the Nb/sub 3/Al strand developed for the ITER project was measured in temperatures from 4.2 to 15 K and in applied magnetic fields up to 16 T. An empirical equation for the critical current density Was obtained by using these data and the pinning force scaling method. The obtained equation is useful in evaluating the performance of the full-size conductor and in establishing the optimum design criteria for the conductor in fusion machines. In this work, we did not take into account the influence of mechanical strain on the strand. I/sub C/ measurement of the strands under mechanical strain will be carried out and an expression for J/sub C/ with the strain will be completed in the next phase.

Effects of strain on the critical current of Bi-2223/Ag tapes

The influence of mechanical strain on the critical current (I/sub C/) is investigated for multi-filamentary Bi-2223/Ag/Ag-0.2wt%Mg-0.3wt%Sb superconducting tapes at liquid nitrogen temperature, 77 K. Several kinds of Bi-2223/Ag tapes with different Ag/SC ratio (2.0, 2.2, and 2.6) and/or number of filaments (19 and 37) are examined. Bending and tensile deformation tests are performed. In the bending deformation tests, decrease of I/sub C/ is observed for the all samples with bending strain above 0.3% and 0.4% in the tests for bent samples and bent-and-re-straightened samples, respectively. The decrease of I/sub C/ is the most sensitive on the bending strain in the 19-filament samples with Ag/SC ratio of 2.0 and the least sensitive in the 37-filament samples with Ag/SC ratio of 2.2. Strain tolerance in the tensile deformation tests varies depending on the number of filaments, although the strain tolerance is similar for the samples with the same number of filaments and different Ag/SC ratio. Large decrease of I/sub C/ is observed for 19-filament and 37-filament samples with Ag/SC ratio of 2.2 at tensile strain above 0.17% and 0.23%, respectively (the tensile strain is the deformation from as-cooled state on Ti-6wt%Al-4wt%V holder). Higher Ag/SC ratio and fine filament are effective to improve the durability against deformation.

Strain effect in MgB 2/stainless steel superconducting tape

The influence of mechanical strain on the critical current ( I c) is investigated for magnesium diboride (MgB 2)/stainless steel (SUS316) superconducting tapes. The tapes are fabricated by using “powder in tube” method and deformation process without any heat treatment. The tensile axial strain along tape length is successfully induced to the sample by using a U-shape holder made of stainless steel (SUS304). Two samples are examined at 4.2 K in 5 T ( B is applied perpendicular to the tape surface). While the initial I c at zero external strain state ( I c0) varies (30.4 and 33.3 A), normalized I c ( I c/ I c0) vs. external strain relations fall on the same curve. Linear increase of I c is observed from zero external strain state to 0.4% strain (107% of I c0). Rapid and large degradation occurs at the strain exceeding 0.4–0.5%. High durability against stress can be expected for MgB 2/stainless steel superconducting tapes.

Strain and fatigue tests of Bi-2223/Ag superconducting tapes

The influence of mechanical strain on I c is investigated for Bi-2223/pure-Ag superconducting tapes at 77 K. Taking into account of the pre-strain due to thermal contraction, all the results for normalized I c vs. strain relation fall on a master curve. Normalized I c values exceed 0.98 in the strain range from −0.2% to 0.2%. The strain test machine can be applicable also for fatigue tests. Application of cyclic strain (0%→ x%→0%) is repeated. Strain cycles with maximum strain ranging from −0.18% to 0.25% cause no significant degradation. The results support the feasibility of HTS conductors for practical applications.

Influence of Mechanical Strain on the Electrical Conductivity of Carbon-Containing Composites

Influence of Mechanical Strain on the Electrical Conductivity of Carbon-Containing Composites

Strain effect in Bi-based oxide/Ag superconducting tapes

The influence of mechanical strain on the critical current (I/sub c/) is investigated for (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/(Bi-2223)/ Ag-0.2wt%Mg-0.3wt%Sb superconducting tapes at 77 K. The tensile axial strain along tape length is successfully induced to the sample by using a U-shape holder. Continuous change of the axial strain can be obtained by changing the distance between both ends of the holder. The U-shape holders made of Ti, SUS304, or brass are used to examine the effect of thermal strain due to the contraction caused by the cooling. For example, the results for the samples glued to Ti or brass holder are as follows. Strain dependence of normalized I/sub c/ (I/sub c//I/sub c/(at as-cooled state)) is affected by holder material. A steep decrease of I/sub c/ occurs when we apply 0.1% and 0.3% strain for Ti and brass holder, respectively. The different thermal expansion (-0.15% for Ti and -0.37% for brass from 300 K to 77 K) explains it. All the results for normalized I/sub c/ vs. strain relation fall on a master curve with taking into account of the effect of the thermal strain. Thermal expansion of the tape from 300 K to 77 K is measured to be -0.35% by using a strain gage. The critical strain ( c) where a steep decrease of I/sub c/ occurs is evaluated to be 0.27% from self-contracted state of the tape.

The influence of strain on confined electronic states in semiconductor quantum structures

A continuum finite element technique is adopted to study electronic properties of submicron electronic devices where function hinges on quantum mechanical effects. Of particular interest is the influence of mechanical strain on confined electronic states. The steady state Schrödinger equation, which governs the electronic behavior of such devices, is modified to include the potential induced by a strain field which is present as a consequence of the fabrication. The governing equation is cast in a variational form, and it is discretized on a standard finite element mesh which is more refined in regions where large quantum mechanical wave function gradients are expected. Multiple energy bands and three-dimensional structures can be considered, and effects including strain enhanced charge confinement and strain induced energy band mixing are studied. As examples, a Ge [5 0 1] faceted island, or quantum dot, on a Si substrate and a Ge v-groove quantum wire on a Si substrate are considered. The technique is used to determine size ranges in which these devices are expected to be most useful. The nonuniform mismatch strain field in the structures is found to affect the energies of experimentally accessible confined states and in some cases to enhance quantum mechanical confinement.

The effect of mechanical strain on hyaluronan metabolism in embryonic fibrocartilage cells.

The development of the synovial joint cavity between the cartilage anlagen of the long bones is thought to be mediated by differential matrix synthesis at the developing articular surfaces. In addition, many studies have shown that removal of movement-induced mechanical stimuli from developing diarthrodial joints prevents cavity formation or produces a secondary fusion of previously cavitated joints. Herein, we describe an inductive influence of mechanical strain on hyaluronan metabolism and the expression of hyaluronan-binding proteins in cultured cells isolated from the articular surface of the distal tibial condyles of 18-day chick embryos. The effect of 10 min of mechanical strain on hyaluronan release into culture media, intracellular uridine diphospho-glucose dehydrogenase activity (an enzyme required for hyaluronan saccharide precursor production), cell surface hyaluronan-binding protein expression and HA synthase mRNA expression were analysed up to 24 h later. Six hours after the application of strain, there was a significant increase in the accumulation of hyaluronan released into tissue culture media by strained fibrocartilage cells compared with controls, an effect still detectable after 24 h. Strained cells also showed increased activity for uridine diphospho-glucose dehydrogenase and expressed higher levels of the hyaluronan-binding protein CD44 at 24 h. In addition, at 24 h mRNA for HA synthase 2 was expressed in all samples whereas mRNA for HA synthase 3 was only expressed in strained cells. These results further highlight the role for movement-induced stimuli in differential extracellular matrix metabolism during joint development and also show that strain may facilitate differential HA synthase gene expression.