Synthesis of few-layered graphene by ion implantation of carbon in nickel thin films

The synthesis of few-layered graphene is performed by ion implantation of carbon species in thin nickel films, followed by high temperature annealing and quenching. Although ion implantation enables a precise control of the carbon content and of the uniformity of the in-plane carbon concentration in the Ni films before annealing, we observe thickness non-uniformities in the synthesized graphene layers after high temperature annealing. These non-uniformities are probably induced by the heterogeneous distribution/topography of the graphene nucleation sites on the Ni surface. Taken altogether, our results indicate that the number of graphene layers on top of Ni films is controlled by the nucleation process on the Ni surface rather than by the carbon content in the Ni film.     

Experimental determination of 3D crack propagation scenario in resistance spot welds of a martensitic stainless steel

International Journal of Fracture - The development of high-performance automotive steels involves increasingly complex chemistries and heat treating sequences, to produce stronger and lighter...     

Carbide Precipitation in 2.25 Cr-1 Mo Bainitic Steel: Effect of Heating and Isothermal Tempering Conditions

The effect of the tempering heat treatment, including heating prior to the isothermal step, on carbide precipitation has been determined in a 2.25 Cr-1 Mo bainitic steel for thick-walled applications. The carbides were identified using their amount of metallic elements, morphology, nucleation sites, and diffraction patterns. The evolution of carbide phase fraction, morphology, and composition was investigated using transmission electron microscopy, X-ray diffraction, as well as thermodynamic calculations. Upon heating, retained austenite into the as-quenched material decomposes into ferrite and cementite. M₇C₃ carbides then nucleate at the interface between the cementite and the matrix, triggering the dissolution of cementite. M₂C carbides precipitate separately within the bainitic laths during slow heating. M₂₃C₆ carbides precipitate at the interfaces (lath boundaries or prior austenite grain boundaries) and grow by attracting nearby chromium atoms, which results in the dissolution of M₇C₃ and, depending on the temperature, coarsening, or dissolution of M₂C carbides, respectively.     

Multi-stage production cost optimization of semi-rigid steel frames using genetic algorithms

The response of a steel structure is closely related to the behavior of its joints. This means that it is necessary to take explicit account of joint properties in order to ensure a consistent approach to design optimization of steel frames. Semi-rigid design has been introduced into steel construction standards such as Eurocode 3 and AISC. However, in the absence of appropriate guidelines, engineers encounter difficulties when bringing in semi-rigid design to everyday engineering practice. Moreover, connection design significantly affects the production cost of steel frame structures. Thus, a realistic optimization of frame design should take into account the effective costs of different stages of production including manufacturing and erection activities. This paper presents a Genetic Algorithm based method for multi-stage cost optimization of steel structures. In the objective function, the total cost of different production stages is minimized. A new cost model is presented that itemizes costs of all stages of production (material supply, manufacturing, erection and foundation). Design examples are used to validate the proposed methodology. Numerical validation shows that the multi-stage design optimization results in substantial cost benefits between 10% and 25% compared to traditional design of steel frames. Furthermore, the developed methodology is shown to be capable of measuring the possible impact of design choices in the early design stage thus assisting designers to make better design decisions.     

Microstructural Characterization of Internal Welding Defects and Their Effect on the Tensile Behavior of FSW Joints of AA2198 Al-Cu-Li Alloy

Internal features and defects such as joint line remnant, kissing bond, and those induced by an initial gap between the two parent sheets were investigated in AA2198-T851 friction stir welded joints. They were compared with the parent material and to defect-free welds obtained using a seamless sheet. The cross-weld tensile strength was reduced by the defects by less than 6 pct. The fracture elongation was not significantly affected in view of experimental scatter. Fracture location, however, changed from the thermomechanically affected zone (retreating side) to the defect in the weld nugget for the welds bearing a kissing bond and for some of the gap welds. The kissing bond was shown by EBSD to be an intergranular feature; it fractured under a normal engineering stress close to 260 MPa during an in situ SEM tensile test. Synchrotron tomography after interrupted tensile testing confirmed opening of the kissing bond. For an initial gap of 23 pct of the sheet thickness, intergranular fracture of copper-enriched or oxide-bearing grain boundaries close to the nugget root was evidenced. The stress and strain state of cross-weld specimens loaded under uniaxial tension was assessed using a 3D finite element, multi-material model, determined on the basis of experimental data obtained on the same specimens using digital image correlation.     

Calculation and mitigation of isotopic interferences in liquid chromatography-mass spectrometry/mass spectrometry assays and its application in supporting microdose absolute bioavailability studies

A methodology for the accurate calculation and mitigation of isotopic interferences in liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) assays and its application in supporting microdose absolute bioavailability studies are reported for the first time. For simplicity, this calculation methodology and the strategy to minimize the isotopic interference are demonstrated using a simple molecule entity, then applied to actual development drugs. The exact isotopic interferences calculated with this methodology were often much less than the traditionally used, overestimated isotopic interferences simply based on the molecular isotope abundance. One application of the methodology is the selection of a stable isotopically labeled internal standard (SIL-IS) for an LC-MS/MS bioanalytical assay. The second application is the selection of an SIL analogue for use in intravenous (i.v.) microdosing for the determination of absolute bioavailability. In the case of microdosing, the traditional approach of calculating isotopic interferences can result in selecting a labeling scheme that overlabels the i.v.-dosed drug or leads to incorrect conclusions on the feasibility of using an SIL drug and analysis by LC-MS/MS. The methodology presented here can guide the synthesis by accurately calculating the isotopic interferences when labeling at different positions, using different selective reaction monitoring (SRM) transitions or adding more labeling positions. This methodology has been successfully applied to the selection of the labeled i.v.-dosed drugs for use in two microdose absolute bioavailability studies, before initiating the chemical synthesis. With this methodology, significant time and cost saving can be achieved in supporting microdose absolute bioavailability studies with stable labeled drugs.     

Specialization Scenarios: A Pragmatic Approach to Declaring Program Specialization

Partial evaluation is a program transformation that automatically specializes a program with respect to invariants. Despite successful application in areas such as graphics, operating systems, and software engineering, partial evaluators have yet to achieve widespread use. One reason is the difficulty of adequately describing specialization opportunities. Indeed, underspecialization or overspecialization often occurs, without any feedback as to the source of the problem. We have developed a high-level, module-based language allowing the program developer to guide the choice of both the code to specialize and the invariants to exploit during the specialization process. To ease the use of partial evaluation, the syntax of this language is similar to the declaration syntax of the target language of the partial evaluator. To provide feedback, declarations are checked during the analyses performed by partial evaluation. The language has been successfully used by a variety of users, including students having no previous experience with partial evaluation.     

Combed single DNA molecules imaged by secondary ion mass spectrometry

Studies of replication, recombination, and rearrangements at the level of individual molecules of DNA are often limited by problems of resolution or of perturbations caused by the modifications that are needed for imaging. The Combing-Imaging by Secondary Ion Mass Spectrometry (SIMS) (CIS) method helps solve these problems by combining DNA combing, cesium flooding, and quantitative imaging via the NanoSIMS 50. We show here that CIS can reveal, on the 50 nm scale, individual DNA fibers labeled with different, nonradioactive isotopes and, moreover, that it can quantify these isotopes so as to detect and measure the length of one or more short nucleic acid fragments associated with a longer fiber.     

Modelling and experimental study of the tertiary creep stage of Grade 91 steel

This article addresses experimental studies and analytical simulations of the tertiary creep stage of Grade 91 steel tested at various stresses and temperatures between 500°C (up to 160 × 10³ h) and 600°C (up to 94 × 10³ h). The strain rate increases after its minimum mainly because of the softening of the material which microstructure evolves strongly during creep deformation. An interrupted creep test shows that necking significantly affects the acceleration of the reduction in cross-section only during the last 10% of the creep lifetime. The Hoff model based on homogeneous reduction of cross-section correctly predicts lifetimes only for high applied stress. The Hart necking model using the Norton power-law allows fair predictions of lifetimes up to 60 × 10³ h at 500°C. The necking model using a modified Norton power-law combined with a material softening term allows predictions of lifetimes for all creep tests, differing from the experimental results by less than 50%, which is consistent with the experimental scatter. The evolution of the cross-section predicted by this model is in agreement with measurements carried out during the interrupted creep test. Two prediction rules for the lifetime prediction are deduced from the necking model that takes into account the material softening. For a large number of tempered martensitic steels, these two criteria bound the experimental lifetimes up to 200 × 10³ h at 500–700°C.     

From a domain analysis to the specification and detection of code and design smells

Code and design smells are recurring design problems in software systems that must be identified to avoid their possible negative consequences on development and maintenance. Consequently, several smell detection approaches and tools have been proposed in the literature. However, so far, they allow the detection of predefined smells but the detection of new smells or smells adapted to the context of the analysed systems is possible only by implementing new detection algorithms manually. Moreover, previous approaches do not explain the transition from specifications of smells to their detection. Finally, the validation of the existing approaches and tools has been limited on few proprietary systems and on a reduced number of smells. In this paper, we introduce an approach to automate the generation of detection algorithms from specifications written using a domain-specific language. This language is defined from a thorough domain analysis. It allows the specification of smells using high-level domain-related abstractions. It allows the adaptation of the specifications of smells to the context of the analysed systems. We specify 10 smells, generate automatically their detection algorithms using templates, and validate the algorithms in terms of precision and recall on Xerces v2.7.0 and GanttProject v1.10.2, two open-source object-oriented systems. We also compare the detection results with those of a previous approach, iPlasma.