Slight Relaxation Research Articles

An atomic study of hydrogen effect on the early stage oxidation of transition metal surfaces

Density functional theory (DFT) and tight-binding quantum chemical molecular dynamics (QCMD) have been applied to analyze the role of interstitial hydrogen in the process of oxygen adsorption to Ni (111) and Cr-doped Ni (111) surfaces and diffusion within these metal surfaces. The DFT calculations demonstrate that the fcc hollow and octahedral sites are the most favorable for hydrogen adsorption on the surface and subsurface, respectively. A clean metal surface has a slight inward relaxation in the topmost layer, whereas the metal atoms show outward relaxation (2%) due to interstitial hydrogen. The adsorption energies of oxygen and OH have decreased to 0.26 and 0.13 eV, respectively, and the metal atomic bond further extended in the range of 1–2% in order to hydrogen remained interstitial site. Hydrogen changes to a negatively charged in the interstitial site by receiving electron. The QCMD results reveal that the oxygen penetration depth increases when hydrogen occupy into interstitial octahedral site. The deeply diffused or interstitial hydrogen receives electrons from the metal. Additionally, interstitial hydrogen initiates the charge transfer and extends the metal atomic bond. The localized process weakens the metal–metal bonds and it makes the surface chemically active for further interaction. This process can help oxygen or other species to diffuse into the structure. As a result, the subsurface hydrogen accelerates the early stage of oxidation initiation.

Evaluation of residual stress relaxation and its effect on fatigue strength of AISI 316L stainless steel ground surfaces: Experimental and numerical approaches

This paper is aimed at evaluating the residual stress relaxation and its effect on the fatigue strength of AISI 316L steel ground surfaces in comparison to electro-polished surfaces. An experimental evaluation was performed using 3-point and 4-point bending fatigue tests at Rσ=0.1 on two sets of notched specimens finished by electro-polishing and grinding. The residual stress fields were measured at the notch root of specimens, before and after fatigue tests, by means of the X-ray diffraction technique. It was found a degradation of about −35% for the 4-point bending fatigue limit at 2×106 cycles of the ground specimens in comparison to the electro-polished ones. This degradation is associated with a slight relaxation of the grinding residual stresses which remain significant tensile stresses at the stabilized state. While under the 3-point bending test, these residual stresses relax completely and provoke a noticeable increase of the fatigue limit estimated at about 50% in comparison to the 4-point bending fatigue test. The numerical evaluation of residual stress relaxation was carried out by FE analyses of the cyclic hardening behaviour of the ground layer. The isotropic and nonlinear kinematic model proposed by Chaboche was used and calibrated for the base material and the ground layer. The results show that residual stresses relax to a stabilized state characterized by elastic-shakedown response. This stabilization is occurred after the first cycle of the 4-point bending test corresponding to the higher stress concentration (Kt-4p=1.66), while it requires many cycles under the 3-point bending test corresponding to the lower stress concentration (Kt-3p=1.54). The incorporation of stabilized residual stress values into the Dang Van’s criterion has permitted to predict with an acceptable accuracy the fatigue limits under both bending modes.

A DFT study of formation energies of Fe–Zn–Al intermetallics and solutes

We report Density Functional Theory results on FeAl and FeZn intermetallics and Fe, Zn and Al solute atoms. The formation energies of fully relaxed intermetallic geometries were determined, as well as solution energies of the three elements in host lattices of the other two elements. Since it is know that the outcome of the magnetic states of some FeAl intermetallics and Fe solutes in Al depends on subtle details of how the calculations are carried out, we have determined many of our results with two different parameterisations, PBE and PBEsol, so see how the parameterisation influences the results.The relaxed intermetallic geometries are in good agreement with experimental results, with PBEsol calculations resulting in slightly smaller geometries than PBE calculations (0.7–2.1%). Intermetallic formation energies fall within ranges of experimental results where available, and are in excellent or reasonable agreement with other DFT results, except for the FeAl2 phase. For this phase a structure revision was recently suggested and the heat of formation of the newly suggested structure is 0.1 eV/atom lower than for the long-accepted structure. The formation energies of Fe aluminides are an order of magnitude more negative than those of FeZn intermetallics. Most of the calculated magnetic states of the intermetallics are at odds with experimental results. However, the intermetallic formation energies are often not strongly affected by this.Fe/Al solute systems have the most negative solution energies. All other solution energies are positive and smaller in absolute value than the Fe/Al solution energies. Solution energies were all some tenths of eV. Where comparisons could be made, calculated and experimental results differed by some hundredths of eV. The magnetic moment found on an Fe solute in Al is at odds with experimental results. As with FeAl, the outcome of the magnetic state subtly depends on the details of how calculations were performed and has little energetic effect. Lattice relaxation around solute atoms is mostly in agreement with simple atomic size considerations. The slight relaxation of Al neighbours away from a Zn solute is at odds with this pattern, and also with experimental results.

Two-Dimensionally Patterned Electrodeposition of Sn Film from Aqueous Acid Bath

The electrodeposition of two-dimensional Sn micropatterns without whisker growth was investigated using an aqueous acid bath. Polyethylene glycol suppressed the growth of Sn normal to the surface of a Cu foil substrate and flat Sn micropatterns were successfully obtained on various different photoresist-patterned Cu foils. The current efficiency of Sn electrodeposition was higher than 97% for all samples, although the pH of the solution was about 0.0, indicating that the overpotential of H2 evolution on the Sn/Cu substrate was quite large. Sn micropatterns, in the form of both lines and circles, showed a slight macroscopic stress relaxation effect. In the present work, we demonstrate the electrodeposition of two- dimensional Sn micropatterns on Cu foils from an aqueous acid bath utilizing a photolithographic technique. The effect of polyethylene glycol on the surface morphology of Sn and the potential change during electrodeposition were also investigated. This work provides general guidelines for the patterned electrodeposition of other types of metals or alloys. Furthermore, we evaluated the stress relaxation effect during lithiation and delithiation using two-dimensional Sn micropatterns as a reference. expose a single side with an area of 20 mm × 20 mm. The masked Cu foils were used as the working electrodes and a carbon substrate was used as the counter electrode. The distance between the working and counter electrodes was set at 10 mm. A saturated calomel electrode (SCE) was used as the reference electrode. The measured poten- tials were converted to values versus the standard hydrogen electrode (SHE) using the following relationship: ESCE= +0.244 V vs. SHE. Sn plating on the Cu surface was conducted at 10 mA cm −2 (effective surfacearea)withapotentiostat/galvanostat(HokutoDenkoCo.,Ltd., Japan, HZ-3000) at room temperature with stirring at 100 rpm. The Sn morphology was observed using afield emission scanning electron microscope (FE-SEM: Hitachi Ltd., S-4300). Charge-discharge tests were conducted at 90 μ Ac m −2 (effec- tive surface area) and room temperature with a charge-discharge unit (Hokuto Denko Co., Ltd., Japan, HJ-1001 SD8) to study the effect of macroscopic stress relaxation of Sn micropatterns during lithia- tion and delithiation. The cutoff potentials were 0.001 V and 2 V vs. Li/Li + . A coin cell was constructed in an Ar atmosphere glove box (M. Braun Inertgas-Systeme GmbH, Germany, MB150-B). Sn- deposited Cu foils and Li metal were used as the positive and negative electrodes, respectively, and 1 M LiPF6 solution of ethylene carbonate and dimethyl carbonate (1:2, v/v) was used as the electrolyte.

Electronic structures and optical properties of CuSCN with Cu vacancies

Based on density functional theory (DFT) within the generalized gradient approximation (GGA) using the CASTEP code, we calculated the formation energy of a Cu vacancy, as well as the band structure and the optical properties of β-CuSCN with Cu vacancies. Removal a Cu atom from the 32-site and the 72-site supercell results in an enlargement of the band-gap and a slight relaxation in the lattice parameter. An accepter level above the valence band maximum is observed in the 32-site supercell with a Cu vacancy, which results in the onset of a small absorption pre-peak at 0.65 eV.

Surface relaxation of topological insulators: Influence on the electronic structure

The surface structure of topological insulators Bi${}_{2}$Te${}_{3}$(111) and a single bilayer bismuth on it was studied by low-energy electron-diffraction analysis. The topmost quintuple layer of Bi${}_{2}$Te${}_{3}$ showed only a slight relaxation ($\ensuremath{\sim}\phantom{\rule{-0.16em}{0ex}}1%$ contraction). On the other hand, the bilayer Bi was strongly distorted compared to bulk Bi (3.5 $\phantom{\rule{-0.16em}{0ex}}%$ in-plane contraction and $\ensuremath{\sim}\phantom{\rule{-0.16em}{0ex}}7%$ out-of-plane expansion). First-principles calculation reveals that this distortion has a large influence on the electronic structure and can enlarge the band gap.

Systematic Modification of Electrical and Superconducting Properties of YBCO and Nano-Patterning of High-Tc Superconducting Thin Films by Light-Ion Irradiation

Abstract Irradiation of high-temperature superconducting (HTS) YBa2Cu3O7-d (YBCO) thin films with 75 keV He + ions leads to a quasi-exponential increase of the in-plane (ρab) and the out-of-plane (ρc) resistivity in the normal state and to a non-linear decrease of the critical temperature Tc with ion dose. In situ electrical measurements at room temperature reveal an irradiation-induced reduction of resistivity anisotropy ρc/ρab and a slight relaxation of film resistivity after the ion irradiation is stopped. Ex situ measurements show a stretched-exponential relaxation of Tc and normal state resistivity that continues for several weeks after the ion irradiation. Irradiation of YBCO thin films by low-energy He + ions through stencil masks results in local modification of the electrical and superconducting properties of the HTS material. We demonstrate that masked ion-beam lithography enables to produce structures smaller than 100 nm in size that have potential for applications in future superconducting nano-electronics.

A Model for Ca(2+)-Dependent Cooperative Activation in the Cardiac Thin Filament that Allows for Crossbridge Cycle Feedback

The mechanism underlying the apparent cooperativity of the cardiac thin filament was investigated by using FRET to follow the N-domain opening of recombinant cardiac troponin C (N-cTnC opening) passively exchanged into rat myocardial fiber bundles and tested under a variety of experimental conditions. Calcium titrations conducted in the presence of crossbridge cycle modulators and tension recovery experiments revealed: 1) N-cTnC opening occurred just as “cooperatively” with or without crossbridge cycle activity; 2) the calcium sensitivity of N-cTnC opening is enhanced by crossbridge cycling; 3) the rigor state results in no cooperativity and 10% of the cTnC ensemble being apparently open under resting conditions; 4) the breaking of crossbridges preceding a tension recovery phase results in a slight relaxation of the FRET distance associated with N-cTnC opening, which recovers during tension recovery.

Solution concepts in vector optimization: a fresh look at an old story

Over the past decades various solution concepts for vector optimization problems have been established and used: among them are efficient, weakly efficient and properly efficient solutions. In contrast to the classical approach, we define a solution to be a set of efficient solutions on which the infimum of the objective function with respect to an appropriate complete lattice (the space of self-infimal sets) is attained. The set of weakly efficient solutions is not considered to be a solution, but weak efficiency is essential in the construction of the complete lattice. In this way, two classic concepts are involved in a common approach. Several different notions of semicontinuity are compared. Using the space of self-infimal sets, we can show that various originally different concepts coincide. A Weierstrass existence result is proved for our solution concept. A slight relaxation of the solution concept yields a relationship to properly efficient solutions.

First-principle calculations of dilute nitride GaP 1− xN x alloy in zinc-blende structures

First-principle plane-wave pseudopotential calculations using the density-functional theory within the local density approximation (LDA) have been carried out to investigate the structural, electronic and thermodynamic properties of zinc-blende dilute nitride GaP 1− x N x alloy. We have found that the unit cell volumes of GaP 1− x N x alloys are smaller than the value calculated from the linear interpolation of GaN and GaP binary alloys and there exists a negative deviation from Vegard's law. The Ga–P and Ga–N bond lengths of GaP 1− x N x alloys reveal a slight relaxation. The incorporation of nitrogen into GaP leads to the giant reduction of the bandgap energy. We have investigated the thermal stabilities and obtained the most stable configurations of the GaP 1− x N x alloy. In addition, the formation enthalpies have also been calculated, which could explain the difficulty in nitrogen incorporation into GaP.

Effects of the strain relaxation of an AlGaN barrier layer induced by various cap layers on the transport properties in AlGaN/GaN heterostructures

The strain relaxation of an AlGaN barrier layer may be influenced by a thin cap layer above, and affects the transport properties of AlGaN/GaN heterostructures. Compared with the slight strain relaxation found in AlGaN barrier layer without cap layer, it is found that a thin cap layer can induce considerable changes of strain state in the AlGaN barrier layer. The degree of relaxation of the AlGaN layer significantly influences the transport properties of the two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures. It is observed that electron mobility decreases with the increasing degree of relaxation of the AlGaN barrier, which is believed to be the main cause of the deterioration of crystalline quality and morphology on the AlGaN/GaN interface. On the other hand, both GaN and AlN cap layers lead to a decrease in 2DEG density. The reduction of 2DEG caused by the GaN cap layer may be attributed to the additional negative polarization charges formed at the interface between GaN and AlGaN, while the reduction of the piezoelectric effect in the AlGaN layer results in the decrease of 2DEG density in the case of AlN cap layer.

Casein-derived tripeptide Ile–Pro–Pro improves angiotensin-(1–7)- and bradykinin-induced rat mesenteric artery relaxation

AimsMilk casein-derived bioactive tripeptides isoleucine–proline–proline (Ile–Pro–Pro) and valine–proline–proline (Val–Pro–Pro) lower blood pressure in animal models of hypertension and humans. In some studies, their angiotensin-converting enzyme (ACE)-inhibitory effect has been demonstrated. Besides classical ACE-angiotensin II-AT1-receptor pathway (ACE-Ang II- AT1), the significance of ACE2-angiotensin-(1–7)-Mas-receptor (ACE2-Ang-(1–7)-Mas) axis in the blood pressure regulation has now been acknowledged. The present study was aimed to further evaluate the renin–angiotensin system (RAS)-related vascular effects of Ile–Pro–Pro in vitro using rat mesenteric arteries. Main methodsSuperior mesenteric arteries of spontaneously hypertensive rat (SHR) were isolated, cut into rings and mounted in standard organ bath chambers. Endothelium-intact arterial rings were incubated in Krebs solution either with Ile–Pro–Pro, proline–proline (Pro–Pro), isoleucine (Ile), proline (Pro) or captopril for 6h at +37°C and vascular reactivity was measured. Key findingsIn the presence of AT1-antagonist valsartan, Ang II induced vasodilatation, which was more pronounced in the arteries incubated with Ile–Pro–Pro (P<0.05) compared to the other compounds. Ang-(1–7)-induced vasodilatation was augmented by Ile–Pro–Pro or Pro (P<0.001 vs. control). Mas-receptor antagonist A-779 did not alter the responses. Ile–Pro–Pro and Pro augmented also bradykinin-induced relaxations (P<0.001 vs. control). Control arteries and arteries incubated with captopril showed only slight relaxations at higher bradykinin concentrations. SignificanceCasein-derived tripeptide Ile–Pro–Pro and amino acid Pro enhance the vasodilatory effect of Ang-(1–7) and bradykinin. The role of ACE2-Ang–(1–7)-Mas axis in the modulation of vascular tone by these compounds seems probable.

Effect of cassia sieberiena leaf extracts on the intestinal motility of rat

The in-vitro effects of methanolic extract (MCSL) and aqueous infusion (ACSL) of the leaves of C. sieberiena on the motility of the rat intestines were studied and compared with those of C. acutifolia(MCAL and ACAL) “Senna”. All the extracts and infusion relaxed the ileum dose-dependently. Their effects were blocked by tolazoline, indicating that á–adrenergic receptors were involved. MCSLcontracted the colon dose-dependently and was blocked by atropine(1.7x10-8 M) and nifedipine (2.8x10-10M). ACSL contracted this segment at 2.0-8.0 mg/ml and relaxed it at 8.0-16.0mg/ml. Itsrelaxant effect was blocked by tolazoline (1.0x10-6M), indicating the involvement of á– adrenergic receptors . MCAL had a slight relaxant effect on the colon, while ACAL contracted it dose dependently and was blocked by promethazine (3.1x10-8M) and nifedipine (2.8 x 10-8M), indicating that H1-receptor stimulation and increased intracellular calcium ion concentration are involved. MCSL was more potent than ACAL, while ACSL and ACAL were equipotent in contracting thecolon. With proper processing C. sieberiena can be substituted for C. acutifolia.

Strain effects on InxAl1−xN crystalline quality grown on GaN templates by metalorganic chemical vapor deposition

In x Al 1 − x N epilayers (∼200 nm thick) under different strain states were grown on GaN templates by metalorganic chemical vapor deposition. When the strain is small (0.166≤x≤0.208), InxAl1−xN epilayers are almost fully coherent with the GaN templates, and the surface presents similar characteristic of small hillocks and uniform pits. In the case of large tensile strain, cracks emerged on the surface, but the surface morphology is less influenced compared to the samples with small strain. However, with large compressive strain, the surface roughness dramatically increased and additional smaller pits emerged with partial strain relaxation occurring during growth. In addition, the microstructures were further investigated by transmission electron microscopy. It is demonstrated that even slight relaxation of compressive strain can lead to notable influence on the structural quality and surface morphology of InxAl1−xN films.

English

The leaf base of&nbsp;Sorghum bicolor&nbsp;(Family: Gramineae, Poaceae) was cold-macerated with 70% v/v methanol. The aqueous methanolic extract was further fractionated into non-polar, medium polar and very polar components using hexane, ethylacetate and water (aqueous), respectively. The gastrointestinal effects of these extracts were tested on intestinal motility (transit) in mice, castor oil-induced diarrhoeal model in rats, isolated rabbit jejunum, guinea pig ileum and rat stomach fundus strip. The oral and intraperitoneal LD50&nbsp;values for the extracts were determined in mice and rats. The aqueous methanolic extract (100 &ndash; 400 mg/kg i.p) significantly (P &lt; 0.05) and dose-dependently decreased the intestinal motility, inhibited castor oil-induced diarrhoea, produced concentration-dependent relaxation of rabbit jejunum with half maximal effective concentration (EC50) of 0.21 mg/ml. This extract also produced both non-myogenic and slight relaxation effects on guinea pig ileum and a contraction on rat stomach fundus strips. Both aqueous and ethylacetate fractions also reduced intestinal motility. However, ethylacetate fraction caused greater reduction than the aqueous fraction. The oral LD50&nbsp;value for the aqueous methanolic extact in both rats and mice was found to be &ge; 2000 mg/kg while the intraperitoneal values are 1414.2 mg/kg in rats and 1341.6 mg/kg in mice. The intrapertoneal value for both aqueous and ethylacetate fractions is &ge; 2000 mg/kg in mice. The study provided scientific bases for the traditional use of&nbsp;S. bicolor&nbsp;for treatment of gastrointestinal related problems such as diarrhoea. &nbsp; Key words:&nbsp;Sorghum bicolor, gastrointestinal, motility, diarrhoea, jejunum, ileum, fundus.

Fatigue Behaviour of Welded High-Strength Steels after High Frequency Mechanical Post-Weld Treatments

Investigations have been carried out regarding the fatigue strength of welded details improved by high frequency treatment methods. These methods increase the fatigue strength by cold forming of the surface, so that the weld toe is smoothened, the surface hardness is increased and compressive residual stresses are present up to a depth of 1 to 1.5 mm. In this paper, the surface residual stresses at the weld toe are investigated before and after different loading conditions and for different steel grades. It is shown that only high tensile fatigue loading can lead to a slight residual stress relaxation for low-strength steels. The fatigue crack behaviour is analysed in more detail. The crack propagation rates with and without surface treatment are investigated, using defined lines of rest. The study shows that crack propagation in the edge layers is reduced. Several cracks may start in the UIT-treated zone but will not propagate further, until one final crack, often close to the edge of the specimens, will lead to failure. The results of fatigue tests for butt welds and longitudinal stiffeners improved by high frequency hammer peening are presented. The fatigue strength is seen to be doubled. For high-strength steels, the improvement at different load levels is identical, but for lower-strength steels, high stress ranges lead to reduced improvement. This fact results in flatter SN-curves and can be explained by the lower maximum of residual stresses and residual stress relaxation.

Serotonin-induced coronary microvessel contractions post cardioplegia, cardiopulmonary bypass are mediated in part via the phospholipase A2 pathway in patients

INTRODUCTION: Vasomotor dysfunction after cardiac surgery with cardioplegia and cardiopulmonary bypass (CPB) is estimated to occur in up to 2.5 % of patients, with EKG changes occurring in up to 8%. This dysfunction is thought to be caused by microvascular spasm and leads to myocardial ischemia and worsening cardiac function postoperatively. Phospholipases are involved in signal transduction pathways and regulate many inflammatory pathways. In this study, we examined the role of phospholipases A2 and C in serotonin-induced vasospasm post-CPB. METHODS: Right atrial tissue was harvested from patients undergoing coronary artery bypass grafting (n 5) before initiation of CPB (pre) and after termination of CPB (post). Cold blood cardioplegia was used. We examined coronary arterioles (70- 180 m) for vascular responses to serotonin alone and in the presence of phospholipase A2 (quinacrine, 10-9 to 10-5 mol/L) or phospholipase C inhibitors (U73122, 10-9 to 10-5 mol/L). RESULTS: Microvessels demonstrated a slight relaxation response to serotonin pre-CPB, which shifted to a strong dose-dependent contraction post-CPB. At the highest concentration, serotonin caused a 18.9%2%contraction.Additionofquinacrinesignificantlyinhib

Investigation of interface characteristics in strained-Si nMOSFETs

We investigate and compare the effects of silicon thicknesses on interface characteristics in strained-Si nMOSFET fabricated on SiGe virtual substrate. Ge out-diffusion effect and slight strain relaxation in Si-cap layer are observed with capacitance–voltage measurements. The low-frequency noise characteristics were used to further investigate the interface transport mechanisms and show the same tendency. Moreover, experimental results show that the unified model, i.e. carrier number fluctuation model, including correlated mobility fluctuation is more suitable to interpret the mechanism of 1/ f noise in strained-Si devices. Carrier number fluctuation dominates the 1/ f noise in weak inversion, but the mobility fluctuation contributes to strong inversion.

Uniformly oriented, ellipsoidal nanovoids in glass created by electric-field-assisted dissolution of metallic nanoparticles

Nanoporous glass containing spherical or ellipsoidal nanovoids, respectively, has been produced by electric-field-assisted dissolution of Ag nanoparticles embedded in glass-metal nanocomposites. Small angle x-ray scattering before and after particle dissolution gives evidence that in the case of spherical nanoparticles the remaining nanovoids have the same size distribution ($\ensuremath{\approx}20\text{ }\text{nm}$ average diameter) as the original silver particles. Spheroidal particles of uniform orientation leave strongly aspherical nanovoids, which undergo a slight shape relaxation from aspect ratio 4.7 (particles) to 3.8 (holes).

In-situ XAS study on Li 2MnSiO 4 and Li 2FeSiO 4 cathode materials

Li 2FeSiO 4/C and Li 2MnSiO 4/C cathode materials were a subject of in-situ characterisations during the first cycle of oxidation/reduction by complementary techniques of X-ray absorption spectroscopy and Mössbauer spectroscopy, whereby the changes in the local environment of Fe (and Mn) are monitored. Both techniques demonstrate the reversibility of monitored parameters of Fe environment during lithium exchange, and hence confirm the cycling stability of the Li 2FeSiO 4/C. The position of Fe in slightly distorted oxygen tetrahedra shifts with the change of valence accompanying Li removal. Outside of the immediate oxygen envelope, in more distant coordination shells, only minor variation in the neighbour distances is detected, apparently due to a slight relaxation of the structure. The oxidation state of Mn in Li 2MnSiO 4/C cathode material changes from the initial Mn(II) to Mn(III) in the potential range from 4.0 to 4.5 V vs. lithium reference but not beyond. During the oxidation, the short Mn O bond decreases from 2.04 to 1.87 Å in the correlation with the increase of Mn valence state, while the larger Mn O distance in the MnO 4 tetrahedron remains unchanged. The reduction is not completely reversible as evident from the distribution of O atoms in the MnO 4 tetrahedron after one oxidation/reduction cycle.