Twin Layers Research Articles

In situ observation of nanotwins formation through twin terrace growth in pulse electrodeposited Cu films

Nanotwinned copper (nt-Cu) shows a broad application prospects as interconnection materials in integrated circuit industry, since it combines the excellent mechanical and electrical properties. However, the formation and growth behavior of twin lamellae in pulse electrodeposited copper films are not fully understood. In this work, a series of electroplated copper films are prepared by verifying the electroplating parameters and the microstructures are analyzed using scanning electron microscope (SEM) and transmission electron microscope (TEM). The surface morphology indicates strong evidence of stacked twin terraces and layers, suggesting that nanotwins grow up layer by layer. Combined with in situ characterization by SEM and molecular dynamics (MD) simulation, it is proved that the terraces originate from the triple junction of grain boundaries and grow up by extending along the lateral (111) crystal plane. A twin terrace-growing model for nt-Cu is then deduced, which distinguishes from deformation twins or annealed twins. This growth model would be prospective to help obtain high quality of nt-Cu in industry.

The drilling of carbon fibre composite–aluminium stacks and its effect on hole quality and integrity

The article details experimental work to evaluate tool wear, cutting forces/torque and associated hole quality/accuracy following single-shot drilling of twin layer CFRP/AA7010 stacks. A full factorial experiment was initially planned involving variation in cutting speed (60 and 120 m/min), feed rate (0.15 and 0.30 mm/rev) and drill tip geometry (double cone and flat point drills). While flank wear for the flat point drills did not exceed 40 µm even after 120 holes irrespective of operating conditions, the double cone geometry suffered catastrophic failure after only four holes at the lowest parameter combination. Therefore, the remaining tests involving the double cone drill at higher operating parameters were subsequently halted. Feed rate had a significant influence on torque in both the CFRP and Al layers, although thrust force and torque generally remained stable over the test duration. Hole diameter was typically up to 34 µm above the nominal value of 6.38 mm with corresponding out of roundness of <60 µm. Burrs were prevalent at hole exit in all tests, with an average height of ∼120 µm when drilling at the highest cutting speed–feed rate parameter combination. Similarly, the delamination factor at hole entry increased by up to 23% when operating at the higher feed rate level.

Microalgal cultivation in porous substrate bioreactor for extracellular polysaccharide production

Netrium digitus is a representative of the species-rich class Zygnematophyceae (Streptophyta). Its intensive extracellular polysaccharide (EPS) production makes this alga interesting for biotechnological applications with a focus on cosmetics and food additives. Quantitative data on growth and EPS production in suspension and, for the first time, in immobilized culture using lab-scale porous substrate bioreactors, so-called Twin-Layer (TL) systems, is presented. It is shown that the cell as well as the EPS dry weight content is increased at least sixfold in immobilized compared to suspension culture. Due to the high amount of EPS, the biofilms reach a thickness of more than 8 mm after 27 days at 70 μmol photons m−2 s−1 and with 1.5% CO2 supply. Frequent exchange of the growth medium results in a linear cell biomass increase of 2.02 ± 0.09 g m−2 growth area day−1 compared to 2.99 ± 0.09 g m−2 day−1, when the medium is not exchanged. Under this mode of cultivation, the EPS production is lower and a final concentration of 12.18 ± 1.25 g m−2 compared to 20.76 ± 0.85 g m−2, when medium was exchanged, is reached. It is clearly demonstrated that the relatively slow growing, but excessively EPS producing, microalgal species N. digitus can be grown in porous substrate bioreactors and that this culturing technique is a promising alternative to suspension culture for the Zygnematophyceae.

Synthesis and study of electrolytic materials with a high-energy defect structure and a developed surface

The defect structure of the electrolytic copper coatings formed upon mechanical activation of a cathode is described. These coatings are shown to have a fragmented structure containing disclination-type defects, namely, terminating dislocation, disclination and twin boundaries; partial disclinations, misorientation bands; and twin layers. They have both growth and deformation origins. The mechanisms of formation of the structural defects are discussed. It is experimentally proved that part of the elastic energy stored in the crystal volume during electrocrystallization can be converted into surface energy. As a result, catalytically active materials with a large developed surface can be synthesized.

A new numerical method for singularly perturbed turning point problems with two boundary layers based on reproducing kernel method

In this paper, a simple numerical method is proposed for solving singularly perturbed boundary layers problems exhibiting twin boundary layers. The method avoids the choice of fitted meshes. Firstly the original problem is transformed into a new boundary value problem whose solution does not change rapidly by a proper variable transformation; then the transformed problem is solved by using the reproducing kernel method. Two numerical examples are given to show the effectiveness of the present method.

Coupled Effects of Strain Rate and Temperature on Deformation Twinning in Cu-Zn Alloy

Cu-Zn alloy is an advanced material with deformation twinning mechanism, which is complicated by coupled effects of temperature and strain rate. In this paper, a theoretical model of Cu-Zn alloy is proposed, which accounts for the coupled effects of strain rate and temperature. The model can accurately predict the experimentally observed tendency of the spacing evolution of twin boundary (TB), and it confirms that low temperature and high strain rate promote deformation twinning. Moreover, it is shown that deformation twining is more susceptible to low temperature than to high strain rate, while TB spacing and twin layer thickness values decrease at high strain rates and low temperatures.

Assessment of the corrosion protection ability of cysteamine and hybrid sol–gel twin layers on copper in 1% NaCl

Significant protection of copper in neutral medium was achieved by grafting of cysteamine-hybrid sol–gel twin layers over copper.

Computational method for singularly perturbed delay differential equations with twin layers or oscillatory behaviour

In this paper, we have presented a computational method for solving singularly perturbed delay differential equations with twin layers or oscillatory behaviour. In this method, the original second order singularly perturbed delay differential equation is replaced by an asymptotically equivalent first order neutral type delay differential equation. Then, we have employed numerical integration and linear interpolation to get tridiagonal system. This tridiagonal system is solved efficiently by using discrete invariant imbedding algorithm. Several model examples are solved, and computational results are presented by taking various values of the delay parameter and perturbation parameter. We have also discussed the convergence of the method.

On the role of acoustic feedback in boundary-layer instability.

In this paper, the classical triple-deck formalism is employed to investigate two instability problems in which an acoustic feedback loop plays an essential role. The first concerns a subsonic boundary layer over a flat plate on which two well-separated roughness elements are present. A spatially amplifying Tollmien-Schlichting (T-S) wave between the roughness elements is scattered by the downstream roughness to emit a sound wave that propagates upstream and impinges on the upstream roughness to regenerate the T-S wave, thereby forming a closed feedback loop in the streamwise direction. Numerical calculations suggest that, at high Reynolds numbers and for moderate roughness heights, the long-range acoustic coupling may lead to absolute instability, which is characterized by self-sustained oscillations at discrete frequencies. The dominant peak frequency may jump from one value to another as the Reynolds number, or the distance between the roughness elements, is varied gradually. The second problem concerns the supersonic 'twin boundary layers' that develop along two well-separated parallel flat plates. The two boundary layers are in mutual interaction through the impinging and reflected acoustic waves. It is found that the interaction leads to a new instability that is absent in the unconfined boundary layer.

Reproducing kernel method for singularly perturbed turning point problems having twin boundary layers

A numerical method is proposed for solving singularly perturbed turning point problems exhibiting twin boundary layers based on the reproducing kernel method (RKM). The original problem is reduced to two boundary layers problems and a regular domain problem. The regular domain problem is solved by using the RKM. Two boundary layers problems are treated by combining the method of stretching variable and the RKM. The boundary conditions at transition points are obtained by using the continuity of the approximate solution and its first derivatives at these points. Two numerical examples are provided to illustrate the effectiveness of the present method. The results compared with other methods show that the present method can provide very accurate approximate solutions.

Twin Layer Iris Certification for Confidential Archive by Conceiving Shares (ICCA-CS)

Iris is one of the most challenging biometric techniques. In many proposed biometric recognition technique, template's are store in the database for comparison. But there exists a vital problem in storing the template in the database since it can be easily bootlegged. In order to overcome these issues a novel method for person identification by their Iris, through securely storing the template is proposed. Visual Cryptography Encryption (VCE) technique is used for securely storing the iris template. By means of VCE, shares are generated for the iris template which is stored in the database instead of storing the entire template. Shares are generated by pixel expansion method. Authentication is provided by comparing the shares. Comparison is done by using Hamming Code. So it is a very effective method of person identification. The proposed method gives an extra security in iris recognition.

Effect of Magnetostatic Energy on the Magnetic Driving Forces and Field Induced Superelastic Behavior in Ni-Mn-Ga

Abstract. Present publication gives a general theoretical concept and also presents the relevant experimental results concerning the effect of the magnetostatic coupling between the twin layers on the magnetic-field-controlled superelastic behavior during the mechanical cycling in magnetic field in Ni-Mn-Ga.

Flexural strengthening of concrete beams using CFRP, GFRP and hybrid FRP sheets

The use of composite materials such as fibre reinforced polymers in strengthening and repairing of structural elements, particularly those made of reinforced concrete, is widely spreading. However, for successful and cost-effective applications, engineers must improve their knowledge with respect to the actual behaviour of strengthened structures. Therefore, glass fibre reinforced polymers, because they are more ductile and cheaper than carbon fibres, can be considered as an alternative solution to repair and strengthen concrete elements.The present study is conducted to examine the efficiency of external strengthening systems for reinforced concrete beams using FRP fabric (Glass–Carbon). In order to address this problem, different strengthening configurations are considered (use of separate unidirectional glass and carbon fibres with some U-anchorages or of bidirectional glass–carbon fibre hybrid fabric).A total of seven flexural strengthened reinforced concrete beams are instrumented and tested under repeated loading sequences using a 4-point bending device to complete a failure analysis. The results for strength, stiffness, ductility and failure modes are discussed for the various strengthening solutions considered. An analytical model to predict the flexural failure of strengthened concrete elements is also developed. The results demonstrate that the model predicts strengthened concrete beam behaviour under applied loads accurately. The present tests also reveal the cost-effectiveness of twin layer glass–carbon FRP fabric as a strengthening configuration for reinforced concrete structures.

Collocation method using artificial viscosity for solving stiff singularly perturbed turning point problem having twin boundary layers

A numerical scheme is proposed to solve singularly perturbed two-point boundary value problems with a turning point exhibiting twin boundary layers. The scheme comprises a B-spline collocation method on a uniform mesh, which leads to a tridiagonal linear system. Asymptotic bounds are established for the derivative of the analytical solution of a turning point problem. The analysis is done on a uniform mesh, which permits its extension to the case of adaptive meshes which may be used to improve the solution. The design of an artificial viscosity parameter is confirmed to be a crucial ingredient for simulating the solution of the problem. Some relevant numerical examples are also illustrated to verify computationally the theoretical aspects.

Numerical simulation on size effect of copper with nano-scale twins

To understand the tensile deformation of electro-deposited Cu with nano-scale twins, a numerical study was carried out based on a conventional theory of mechanism-based strain gradient plasticity (CMSG). The concept of twin lamella strengthening zone was used in terms of the cohesive interface model to simulate grain-boundary sliding and separation. The model included a number of material parameters, such as grain size, elastic modulus, plastic strain hardening exponent, initial yield stress, as well as twin lamellar distribution, which may contribute to size effects of twin layers in Cu polycrystalline. The results provide information to understand the mechanical behaviors of Cu with nano-scale growth twins.

A parameter uniform B-spline collocation method for solving singularly perturbed turning point problem having twin boundary layers

A numerical scheme is proposed to solve singularly perturbed two-point boundary value problems with a turning point exhibiting twin boundary layers. The scheme comprises B-spline collocation method on a non-uniform mesh of Shishkin type. Asymptotic bounds are established for the derivative of the analytical solution of a turning point problem. The present method is boundary layer resolving as well as second-order accurate in the maximum norm. A brief analysis has been carried out to prove the uniform convergence with respect to the singular perturbation parameter ϵ by decomposing the solution into smooth and singular components. Some relevant numerical examples are also illustrated to verify computationally the theoretical aspects.

Phase transition in twinned nanolayered silicon structures under uniaxial compression: Molecular dynamics simulations and first-principles total-energy calculations

Molecular dynamics simulations and first-principles total-energy calculations were carried out to investigate the behavior of nanolayered (111) twinned silicon structures under uniaxial compression. The diamondlike silicon structure inside the thin $(<3\text{ }\text{nm})$ twin layers was found to transform to the orthorhombic structure (space group $Fmmm$) at $\ensuremath{\sim}25\text{ }\text{GPa}$ under uniaxial compression and to the tetragonal structure (space group $I4/mmm$) upon decompression. The first structural transformation is a first-order phase transition and the new structure is characterized by an increased failure stress above 37 GPa. First-principles pseudopotential calculations confirmed the formation of the tetragonal phase and showed that both the orthorhombic and tetragonal phases would possess metal properties.

Poly[(μ3-5-bromonicotinato)(5-bromonicotinato)copper(II)

The title coordination polymer, [Cu(C6H3BrNO2)2]n, is composed of two structurally similar two-dimensional coordination polymers (twin layers). Both of them have the same chemical composition but they display different bond lengths and angles. In each layer, two N atoms and four carboxyl­ate O atoms from the bridging 5-bromo­nicotinate ligands and four carboxyl­ate O atoms from the terminal 5-bromo­nicotinate ligands bind to two CuII atoms to form a dinuclear paddle-wheel-like pattern. Adjacent paddle wheels are further linked by bridging 5-bromo­nicotinate groups to generate a two-dimensional coordination polymer; neighboring twin-like layers are finally stacked through π–π stacking interactions between adjacent pyridine rings [perpendicular distance of 3.626 (2) Å] in a ‘sandwich’ manner, thus generating a three-dimensional supra­molecular structure.

Rock magnetic identification and geochemical process models of greigite formation in Quaternary marine sediments from the Gulf of Mexico (IODP Hole U1319A)

A 160 m mostly turbiditic late Pleistocene sediment sequence (IODP Expedition 308, Hole U1319A) from the Brazos-Trinity intraslope basin system off Texas was investigated with paleo- and rock magnetic methods. Numerous layers depleted in iron oxides and enriched by the ferrimagnetic iron-sulfide mineral greigite (Fe 3S 4) were detected by diagnostic magnetic properties. From the distribution of these layers, their stratigraphic context and the present geochemical zonation, we develop two conceptual reaction models of greigite formation in non-steady depositional environments. The “sulfidization model” predicts single or twin greigite layers by incomplete transformation of iron monosulfides with polysulfides around the sulfate methane transition (SMT). The “oxidation model” explains greigite formation by partial oxidation of iron monosulfides near the iron redox boundary during periods of downward shifting oxidation fronts. The stratigraphic record provides evidence that both these greigite formation processes act here at typical depths of about 12–14 mbsf and 3–4 mbsf. Numerous “fossil” greigite layers most likely preserved by rapid upward shifts of the redox zonation denote past SMT and sea floor positions characterized by stagnant hemipelagic sedimentation conditions. Six diagenetic stages from a pristine magnetite-dominated to a fully greigite-dominated magnetic mineralogy were differentiated by combination of various hysteresis and remanence parameters.

Caudal end of the rat spinal dorsal horn

We have previously demonstrated that the transformation of the caudal spinal cord through the conus medullaris to the filum terminale takes place in three steps. In the conus medullaris the twin layers of CGRP-immunoreactive and IB4-labeled primary afferent fibers as well as the translucent portion of the superficial dorsal horn equivalent to the substantia gelatinosa discontinue before the complete removal of the dorsal horn. Parallel with these changes VGLUT1-immunoreactive myelinated primary afferent fibers arborize not only in the deep layers but also in the entire extension of the remaining dorsal horn, while scattered CGRP fibers still remains at the margin of and deep in the dorsal horn. PKCgamma-immunoreactive dorsal horn neurons discontinue parallel with the disappearance of the IB4-labeled nerve fibers. These observations suggest that in the dorsal horn certain neurons are linked to the substantia gelatinosa, while others are substantia gelatinosa-independent neurons.