Designing ultrafine lamellar eutectic structure in bimodal titanium alloys by semi-solid sintering

We report on a novel approach to design typical ultrafine lamellar eutectic structure in bimodal alloys fabricated by semi-solid sintering (SSS) of a eutectic mixture. In our work ultrafine lamellar eutectic structure was implemented by controlling the phase composition of eutectic reaction and consequently by regulating the structure of eutectic reaction-induced liquid phase through varying component number. Microstructure analysis indicate that although all SSSed alloys have the same three phase constitutions of bcc beta-Ti(Fe Co) and fcc Ti-2(Co Fe) the morphology and distribution of the eutectic structure transforms from limited length and minor quantity to partial fine alternating bcc beta-Ti and bcc Ti(Fe Co) lamellae and further to typical complete ultrafine alternating continuous lamellae in the SSSed ternary Ti-Fe-Co quaternary Ti-Fe-Co-Nb and quinary Ti-Fe-Co-Nb-Al alloys. Interestingly the SSSed Ti-Fe-Co-Nb-Al alloy presents a novel bimodal microstructure of coarse fcc Ti-2(Co Fe) surrounded by an ultrafine lamellar eutectic matrix containing ultrafine bcc beta-Ti and bcc Ti(Fe Co) lamellae. This bimodal microstructure exhibits ultra-high yield strength of 2050 MPa with plasticity in compression of 19.7% which exceed published values of equivalent materials. Our results provide a novel pathway for fabricating new-structure metallic alloys for high-performance structural applications. (C) 2017 Elsevier B.V. All rights reserved.</p

A Microscopic Analysis of Premixed Hydrogen-Oxygen Auto-ignition

Combustion is a complex problem involving multi-stage chemical reactions and multi-scale physics. The microscopic process of chemical reactions has obvious stochastic character and may bring important influence to combustion phenomena both locally and globally. In this study, we employ a stochastic simulation algorithm (SSA) to simulate the microscopic hydrogen-oxygen auto-ignition process. Statistical result of SSA calculation shows that fluctuation is controlled by both temperature and microscopic volume. The non-homogeneous distribution of radicals caused by local fluctuation may cause the difference between average microscopic quantities and their macroscopic counterparts due to some radical-radical reactions

Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine

[This corrects the article DOI: 10.1186/s13054-016-1208-6.]

Pan-cancer analysis of whole genomes

Cancer is driven by genetic change, and the advent of massively parallel sequencing has enabled systematic documentation of this variation at the whole-genome scale(1-3). Here we report the integrative analysis of 2,658 whole-cancer genomes and their matching normal tissues across 38 tumour types from the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium of the International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA). We describe the generation of the PCAWG resource, facilitated by international data sharing using compute clouds. On average, cancer genomes contained 4-5 driver mutations when combining coding and non-coding genomic elements; however, in around 5% of cases no drivers were identified, suggesting that cancer driver discovery is not yet complete. Chromothripsis, in which many clustered structural variants arise in a single catastrophic event, is frequently an early event in tumour evolution; in acral melanoma, for example, these events precede most somatic point mutations and affect several cancer-associated genes simultaneously. Cancers with abnormal telomere maintenance often originate from tissues with low replicative activity and show several mechanisms of preventing telomere attrition to critical levels. Common and rare germline variants affect patterns of somatic mutation, including point mutations, structural variants and somatic retrotransposition. A collection of papers from the PCAWG Consortium describes non-coding mutations that drive cancer beyond those in the TERT promoter(4); identifies new signatures of mutational processes that cause base substitutions, small insertions and deletions and structural variation(5,6); analyses timings and patterns of tumour evolution(7); describes the diverse transcriptional consequences of somatic mutation on splicing, expression levels, fusion genes and promoter activity(8,9); and evaluates a range of more-specialized features of cancer genomes(8,10-18).Peer reviewe

Point, surface and volumetric heat sources in the thermal modelling of selective laser melting

Selective laser melting (SLM) is a powder based additive manufacturing technique suitable for producing high precision metal parts. However, distortions and residual stresses within products arise during SLM because of the high temperature gradients created by the laser heating. Residual stresses limit the load resistance of the product and may even lead to fracture during the built process. It is therefore of paramount importance to predict the level of part distortion and residual stress as a function of SLM process parameters which requires a reliable thermal modelling of the SLM process. Consequently, a key question arises which is how to describe the laser source appropriately. Reasonable simplification of the laser representation is crucial for the computational efficiency of the thermal model of the SLM process. In this paper, first a semi-analytical thermal modelling approach is described. Subsequently, the laser heating is modelled using point, surface and volumetric sources, in order to compare the influence of different laser source geometries on the thermal history prediction of the thermal model. The present work provides guidelines on appropriate representation of the laser source in the thermal modelling of the SLM process.Structural Optimization and Mechanic

Computationally efficient thermal-mechanical modelling of selective laser melting

The Selective laser melting (SLM) is a powder based additive manufacturing (AM) method to produce high density metal parts with complex topology. However, part distortions and accompanying residual stresses deteriorates the mechanical reliability of SLM products. Modelling of the SLM process is anticipated to be instrumental for understanding and predicting the development of residual stress field during the build process. However, SLM process modelling requires determination of the heat transients within the part being built which is coupled to a mechanical boundary value problem to calculate displacement and residual stress fields. Thermal models associated with SLM are typically complex and computationally demanding. In this paper, we present a simple semi-analytical thermal-mechanical model, developed for SLM that represents the effect of laser scanning vectors with line heat sources. The temperature field within the part being build is attained by superposition of temperature field associated with line heat sources in a semi-infinite medium and a complimentary temperature field which accounts for the actual boundary conditions. An analytical solution of a line heat source in a semi-infinite medium is first described followed by the numerical procedure used for finding the complimentary temperature field. This analytical description of the line heat sources is able to capture the steep temperature gradients in the vicinity of the laser spot which is typically tens of micrometers. In turn, semi-analytical thermal model allows for having a relatively coarse discretisation of the complimentary temperature field. The temperature history determined is used to calculate the thermal strain induced on the SLM part. Finally, a mechanical model governed by elastic-plastic constitutive rule having isotropic hardening is used to predict the residual stresses.Structural Optimization and Mechanic

MOOC-Rec: Instructional Video Clip Recommendation for MOOC Forum Questions

In this work, we address the information overload issue that learners in Massive Open Online Courses (MOOCs) face when attempting to close their knowledge gaps via the use of MOOC discussion forums. To this end, we investigate the recommendation of one-minute-resolution video clips given the textual similarity between the clips’ transcripts and MOOC discussion forum entries. We first create a large-scale dataset from Khan Academy video transcripts and their forum discussions. We then investigate the effectiveness of applying pre-trained transformers-based neural retrieval models to rank video clips in response to a forum discussion. The retrieval models are trained with supervised learning and distant supervision to effectively leverage the unlabeled data—which accounts for more than 80% of all available data. Our experimental results demonstrate that the proposed method is effective for this task, by outperforming a standard baseline by 0.208 on the absolute change in terms of precision.Web Information System

Integrated Safety and Security Management to Tackle Domino Effects

Domino effects may be induced by both intentional and unintentional threats. To deal with possible intentional and unintentional domino effects, this chapter develops an integrated safety and security management framework. First, safety and security management principles are introduced to show the similarities and differences between safety management and security management. Then an integrated safety and security management framework is proposed based on risk assessment and management principles. In this framework, safety measures and security measures are integrated and divided into three categories: detection measures, delay measures, and emergency response actions. This framework mainly consists of six parts: chemical plant description, threat and hazard identification, the vulnerability of installations subject to hazards and threats, the vulnerability of installations exposed to domino effects, consequence analysis, risk treatment, and risk reduction. According to the framework, protection strategies encompassing both safety and security can be formulated to obtain an acceptable domino effect risk.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Safety and Security Scienc

Risk Assessment of Coupled Hazardous Scenarios

In a coupled domino effect, hazardous scenarios such as toxic release, VCE, and fire can simultaneously or sequentially occur. Chapters 2 and 3 only consider domino effects that are caused by fire or VCE. Therefore, this study develops a dynamic method called “Dynamic Graph Monte Carlo” (DGMC) to model the evolution of coupled domino effects and assess the vulnerability of humans and installations exposed to such scenarios. In the DGMC model, a chemical plant is represented by a system with multiple agents. The system consists of three types of agents: hazardous installations, ignition sources, and humans. Monte Carlo simulation is used to address the uncertainties in the evolution and interdependencies among the agents. By applying the developed algorithm, the death probability of humans and the failure probability of installations exposed to multiple possible hazardous scenarios can be obtained. Moreover, we can also obtain the possible evolution paths, evolution time nodes, and ignition times by using the developed model and algorithm.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Safety and Security Scienc

Dynamic Assessment of VCE-Induced Domino Effects

Vapor cloud explosion (VCE) accidents such as the Jaipur explosion in 2005 manifest that VCEs may lead to unpredicted overpressures, resulting in catastrophic domino effects. Many attempts have been made to assess VCEs and the subsequent domino effects in the process and chemical industry, whereas little attention has been paid to the spatial–temporal evolution of VCEs. Thus, this chapter provides a dynamic methodology based on the discrete dynamic event tree to assess the likelihood of VCEs and possible subsequent domino effects. The developed methodology includes six steps: identification and characterization of loss of containment scenarios, analysis of vapor cloud dispersion, identification and characterization of ignition sources, explosion frequency assessment, overpressure calculation, and escalation assessment. Given a release scenario, by applying the developed methodology, we can obtain the probability of VCEs, the likelihood of domino effects, and the damage probabilities of installations exposed to overpressure.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Safety and Security Scienc