The three-dimensional distribution of individual hydrogen atoms within a complex steel microstructure is characterized using isotopic doping and cryogenic-transfer atom probe tomography.
AbstractThe design of atomic-scale microstructural traps to limit the diffusion of hydrogen is one key strategy in the development of hydrogen-
Hydrogen embrittlement is a complex phenomenon, involving several lengthand timescales, that affects a large class of metals. It can significantly reduce the ductility and load-bearing capacity and cause cracking and catastrophic brittle failures at stresses below the yield stress of susceptible materials. Despite a large research effort in attempting to understand the mechanisms of failure and in developing potential mitigating solutions, hydrogen embrittlement mechanisms are still not completely understood. There are controversial opinions in the literature regarding the underlying mechanisms and related experimental evidence supporting each of these theories. The aim of this paper is to provide a detailed review up to the current state of the art on the effect of hydrogen on the degradation of metals, with a particular focus on steels. Here, we describe the effect of hydrogen in steels from the atomistic to the continuum scale by reporting theoretical evidence supported by quantum calculation and modern experimental characterisation methods, macroscopic effects that influence the mechanical properties of steels and established damaging mechanisms for the embrittlement of steels. Furthermore, we give an insight into current approaches and new mitigation strategies used to design new steels resistant to hydrogen embrittlement.
Hydrogen embrittlement of high-strength steel is an obstacle for using these steels in sustainable energy production. Hydrogen embrittlement involves hydrogen-defect interactions at multiple-length scales. However, the challenge of measuring the precise location of hydrogen atoms limits our understanding. Thermal desorption spectroscopy can identify hydrogen retention or trapping, but data cannot be easily linked to the relative contributions of different microstructural features. We used cryo-transfer atom probe tomography to observe hydrogen at specific microstructural features in steels. Direct observation of hydrogen at carbon-rich dislocations and grain boundaries provides validation for embrittlement models. Hydrogen observed at an incoherent interface between niobium carbides and the surrounding steel provides direct evidence that these incoherent boundaries can act as trapping sites. This information is vital for designing embrittlement-resistant steels.
We report theoretical and experimental evidence that EuCd2As2 in magnetic fields greater than 1.6 T applied along the c axis is a Weyl semimetal with a single pair of Weyl nodes. Ab initio electronic structure calculations, verified at zero field by angle-resolved photoemission spectra, predict Weyl nodes with wavevectors k = (0, 0, ±0.03) × 2π/c at the Fermi level when the Eu spins are fully aligned along the c axis. Shubnikov-de Haas oscillations measured in fields parallel to c reveal a cyclotron effective mass of m * c = 0.08 me and a Fermi surface of extremal area Aext = 0.24 nm −2 , corresponding to 0.1% of the area of the Brillouin zone. The small values of m * c and Aext are consistent with quasiparticles near a Weyl node. The identification of EuCd2As2 as a model Weyl semimetal opens the door to fundamental tests of Weyl physics.
BackgroundWorldwide 350 million people suffer from major depression, with the majority of cases
occurring in low- and middle-income countries. We examined the patterns, correlates and
care-seeking behaviour of adults suffering from major depressive episode (MDE) in
China.MethodA nationwide study recruited 512 891 adults aged 30–79 years from 10 provinces across
China during 2004–2008. The 12-month prevalence of MDE was assessed by the Modified
Composite International Diagnostic Interview-short form. Logistic regression yielded
adjusted odds ratios (ORs) of MDE associated with socio-economic, lifestyle and
health-related factors and major stressful life events.ResultsOverall, 0.7% of participants had MDE and a further 2.4% had major depressive symptoms.
Stressful life events were strongly associated with MDE [adjusted OR 14.7, 95%
confidence interval (CI) 13.7–15.7], with a dose–response relationship with the number
of such events experienced. Family conflict had the highest OR for MDE (18.9, 95% CI
16.8–21.2) among the 10 stressful life events. The risk of MDE was also positively
associated with rural residency (OR 1.5, 95% CI 1.4–1.7), low income (OR 2.3, 95% CI
2.1–2.4), living alone (OR 2.6, 95% CI 2.3–3.0), smoking (OR 1.4, 95% CI 1.3–1.6) and
certain other mental disorders (e.g. anxiety, phobia). Similar, albeit weaker,
associations were observed with depressive symptoms. Among those with MDE, about 15%
sought medical help or took psychiatric medication, 15% reported having suicidal
ideation and 6% reported attempting suicide.ConclusionsAmong Chinese adults, the patterns and correlates of MDE were generally consistent with
those observed in the West. The low rates of seeking professional help and treatment
highlight the great gap in mental health services in China.
Quasiparticle dynamics across the full Brillouin zone of Bi2Sr2CaCu2O8+δ traced with ultrafast time and angle-resolved photoemission spectroscopy Struct. Dyn. 2, 054501 (2015);
Functional magnetic resonance imaging (fMRI), which allows non-invasive mapping of human cognitive functions, has become an important tool for understanding language function. An understanding of component processes and sources of noise in the images is contributing to increased confidence in the reproductability of studies. This allows clinical applications, e.g., for pre-surgical lateralisation of language functions in patients with temporal lobe epilepsy. fMRI is a sensitive method for mapping regions involved in language functions. We recently have applied it to study the effect of word surface form on reading with a comparison of responses to Chinese characters or alphabetical Pinyin. Interpretation of fMRI activations must be made with caution; fMRI suggests task-associated activation, but does not independently confirm that such activity is necessary. However, complementary studies can be performed using transcranial magnetic stimulation (TMS), which can be used to interfere with brain activity in a specific region transiently for characterisation of the behavioural effects. We describe how TMS combined with fMRI has confirmed a role for the left inferior frontal cortex in semantic processing.
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