Liquid-like atoms in dense-packed solid glasses.

Revealing the microscopic structural and dynamic pictures of glasses is a long-standing challenge for scientists1,2. Extensive studies on the structure and relaxation dynamics of glasses have constructed the current classical picture3-5: glasses consist of some 'soft zones' of loosely bound atoms embedded in a tightly bound atomic matrix. Recent experiments have found an additional fast process in the relaxation spectra6-9, but the underlying physics of this process remains unclear. Here, combining extensive dynamic experiments and computer simulations, we reveal that this fast relaxation is associated with string-like diffusion of liquid-like atoms, which are inherited from the high-temperature liquids. Even at room temperature, some atoms in dense-packed metallic glasses can diffuse just as easily as they would in liquid states, with an experimentally determined viscosity as low as 107 Pa·s. This finding extends our current microscopic picture of glass solids and might help establish the dynamics-property relationship of glasses4.

Rejuvenation of metallic glasses by non-affine thermal strain.

When a spatially uniform temperature change is imposed on a solid with more than one phase, or on a polycrystal of a single, non-cubic phase (showing anisotropic expansion-contraction), the resulting thermal strain is inhomogeneous (non-affine). Thermal cycling induces internal stresses, leading to structural and property changes that are usually deleterious. Glasses are the solids that form on cooling a liquid if crystallization is avoided--they might be considered the ultimate, uniform solids, without the microstructural features and defects associated with polycrystals. Here we explore the effects of cryogenic thermal cycling on glasses, specifically metallic glasses. We show that, contrary to the null effect expected from uniformity, thermal cycling induces rejuvenation, reaching less relaxed states of higher energy. We interpret these findings in the context that the dynamics in liquids become heterogeneous on cooling towards the glass transition, and that there may be consequent heterogeneities in the resulting glasses. For example, the vibrational dynamics of glassy silica at long wavelengths are those of an elastic continuum, but at wavelengths less than approximately three nanometres the vibrational dynamics are similar to those of a polycrystal with anisotropic grains. Thermal cycling of metallic glasses is easily applied, and gives improvements in compressive plasticity. The fact that such effects can be achieved is attributed to intrinsic non-uniformity of the glass structure, giving a non-uniform coefficient of thermal expansion. While metallic glasses may be particularly suitable for thermal cycling, the non-affine nature of strains in glasses in general deserves further study, whether they are induced by applied stresses or by temperature change.

[Situation analysis of timing of first visit of anti-mitochondrial antibody-positive patients].

Objective: To understand the basic information of anti-mitochondrial antibody (anti-AMA)-positive patients after initial diagnosis, and to set groundwork for further exploring the clinical significance of AMA in various diseases. Methods: Demographic data and related clinical information recorded through the Information System of Peking University People's Hospital from January 2013 to December 2016 were collected. Patients whose AMA and/or AMA-M2 first- tested as positive were recorded. Complications were classified according to the International Classification of Diseases. Results: A total of 1323 AMA positive cases were discovered for the first time. Among them, 78.0% were women, and the age of initial diagnosis was 56.8 ± 16.0 years. The first three initially diagnosed departments were rheumatology and immunology (37.4%), liver Disease (15.9%) and hematology (15.9%) relevant to musculoskeletal and connective tissue diseases (45.2%), hematology and hematopoietic organs and immune diseases (30.6%) and circulatory system diseases (29.7%). There were 297 newly confirmed cases of primary biliary cholangitis (PBC); accounting for 89.2% of women, and the age of initial diagnosis was 60.1 ± 12.4 years. The top three departments of initially diagnosed as PBC were liver disease (37.7%), rheumatology (33.0%) and gastroenterology (15.2%), of which 39.7% had musculoskeletal and connective tissue diseases, 27.9% had circulatory diseases, and 24.9 % were combined with endocrine and metabolic diseases. Conclusion: Besides PBC and other autoimmune diseases, AMA and / or AMA-M2 positivity can be observed in a variety of diseases in several clinical departments, and its clinical significance remains to be further clarified.

Relaxation Decoupling in Metallic Glasses at Low Temperatures.

Upon cooling, glass-forming liquids experience a dynamic decoupling in the fast ß and slow α process, which has greatly influenced glass physics. By exploring an extremely wide temporal and temperature range, we find a surprising gradual change of the relaxation profile from a single-step to a two-step decay upon cooling in various metallic glasses. This behavior implies a decoupling of the relaxation in two different processes in a glass state: a faster one likely related to the anomalous stress-dominated microscopic dynamics, and a slower one associated with subdiffusive motion at larger scales with a broader distribution of relaxation times.

Fast Surface Dynamics of Metallic Glass Enable Superlatticelike Nanostructure Growth.

Contrary to the formation of complicated polycrystals induced by general crystallization, a modulated superlatticelike nanostructure, which grows layer by layer from the surface to the interior of a Pd_{40}Ni_{10}Cu_{30}P_{20} metallic glass, is observed via isothermal annealing below the glass transition temperature. The generation of the modulated nanostructure can be solely controlled by the annealing temperature, and it can be understood based on the fast dynamic and liquidlike behavior of the glass surface. The observations have implications for understanding the glassy surface dynamics and pave a way for the controllable fabrication of a unique and sophisticated nanostructure on a glass surface to realize the properties' modification.

Size effect on dynamics and glass transition in metallic liquids and glasses.

The relaxation dynamics and glass transition in finite-sized metallic liquid droplets were investigated via molecular dynamic simulations in model monoatomic Ta and binary Cu50Zr50 metallic liquids. We find that the droplet size has a significant impact on liquid dynamics and glass transition. Glass transition temperature and structural relaxation time exhibit strong size dependence and decrease drastically as the droplet is smaller than a certain size. It is revealed that this results from a liquid-like surface layer (∼1 nm thick) of droplets, in which the dynamics is much faster than the interior of droplets. A proposed scaling relationship can well describe the size dependent behavior of the glass transition temperature in metallic liquid droplets. These findings provide insight into the dynamics of metallic liquid droplets and plausible understanding of recent novel experimental observations. Apart from temperature and pressure, size may be another important parameter for potentially tuning the properties of metallic liquids and glasses in nanometer scale.

Memory Effect Manifested by a Boson Peak in Metallic Glass.

We explore the correlation between a boson peak and structural relaxation in a typical metallic glass. Consistent with enthalpy recovery, a boson peak shows a memory effect in an aging-and-scan procedure. Single-step isothermal aging produces a monotonic decrease of enthalpy and boson peak intensity; for double-step isothermal aging, both enthalpy and boson peak intensity experience, coincidently, an incipient increase to a maximum and a subsequent decrease toward the equilibrium state. Our results indicate a direct link between slow structural relaxation and fast boson peak dynamics, which presents a profound understanding of the two dynamic behaviors in glass.

Effects of atomic interaction stiffness on low-temperature relaxation of amorphous solids.

While low-temperature relaxations show significant differences among metallic glasses with different compositions, the underlying mechanism remains mysterious. Using molecular dynamics simulation, low-temperature relaxation of amorphous solids is investigated in model systems with different atomic interaction stiffness. It was found that as the interaction stiffness increases, the low-temperature relaxation is enhanced. The fraction of mobile atoms increases with increasing interaction stiffness, while the length scale of dynamical heterogeneity does not change. The enhanced relaxation may be due to increased dynamical heterogeneity. These findings provide a physical picture for better understanding the origin of low-temperature relaxation dynamics in amorphous solids, and the experimentally observed different ß-relaxation behaviors in various metallic glasses.

A fast dynamic mode in rare earth based glasses.

Metallic glasses (MGs) usually exhibit only slow ß-relaxation peak, and the signature of the fast dynamic is challenging to be observed experimentally in MGs. We report a general and unusual fast dynamic mode in a series of rare earth based MGs manifested as a distinct fast ß'-relaxation peak in addition to slow ß-relaxation and α-relaxation peaks. We show that the activation energy of the fast ß'-relaxation is about 12RTg and is equivalent to the activation of localized flow event. The coupling of these dynamic processes as well as their relationship with glass transition and structural heterogeneity is discussed.

Revealing ß-relaxation mechanism based on energy distribution of flow units in metallic glass.

The ß-relaxation, which is the source of the dynamics in glass state and has practical significance to relaxation and mechanical properties of glasses, has been an open question for decades. Here, we propose a flow unit perspective to explain the structural origin and evolution of ß-relaxation based on experimentally obtained energy distribution of flow units using stress relaxation method under isothermal and linear heating modes. Through the molecular dynamics simulations, we creatively design various artificial metallic glass systems and build a direct relation between ß-relaxation behavior and features of flow units. Our results demonstrate that the ß-relaxation in metallic glasses originates from flow units and is modulated by the energy distribution of flow units, and the density and distribution of flow units can effectively regulate the ß-relaxation behavior. The results provide a better understanding of the structural origin of ß-relaxation and also afford a method for designing metallic glasses with obvious ß-relaxation and better mechanical properties.

Communication: Non-monotonic evolution of dynamical heterogeneity in unfreezing process of metallic glasses.

The relaxation dynamics in unfreezing process of metallic glasses is investigated by the activation-relaxation technique. A non-monotonic dynamical microstructural heterogeneities evolution with temperature is discovered, which confirms and supplies more features to flow units concept of glasses. A flow unit perspective is proposed to microscopically describe this non-monotonic evolution of the dynamical heterogeneities as well as its relationship with the deformation mode development of metallic glasses.

Flow unit perspective on room temperature homogeneous plastic deformation in metallic glasses.

A mandrel winding method, which can realize remarkable homogeneous plastic deformation at room temperature for various metallic glasses, is applied to characterize plastic flow units and study their relationship with macroscopic deformations and relaxations. The method can provide information on the activation energy, activation time, size, intrinsic relaxation time, distribution, and density of flow units. We find the plasticity of a metallic glass can be controlled through modulating the features of flow units. The results have benefits for better understanding the structural origins of deformations and relaxations, and for designing metallic glasses with improved performances.

Compositional origin of unusual ß-relaxation properties in La-Ni-Al metallic glasses.

The ß-relaxation of metallic glasses (MGs) bears nontrivial connections to their microscopic and macroscopic properties. In an effort to elucidate the mechanism of the ß-relaxation, we studied by dynamical mechanical measurements the change of its properties on varying the composition of La60Ni15Al25 in various ways. The properties of the ß-relaxation turn out to be very sensitive to the composition. It is found that the isochronal loss peak temperature of ß-relaxation, Tß,peak, is effectively determined by the total (La + Ni) content. When Cu is added into the alloy to replace either La, Ni, or Al, the Tß,peak increases with decrease of the (La + Ni) content. The trend is in accordance with data of binary and ternary MGs formed from La, Ni, Al, and Cu. Binary La-Ni MGs have pronounced ß-relaxation loss peaks, well separated from the α-relaxation. In contrast, the ß-relaxation is not resolved in La-Al and La-Cu MGs, showing up as an excess wing. For the ternary La-Ni-Al MGs, increase of La or Ni content is crucial to lower the Tß,peak. Keeping the Al content fixed, increase of La content lowers the Tß,peak further, indicating the more important role La plays in lowering Tß,peak than Ni. The observed effects on changing the composition of La60Ni15Al25 lead to the conclusion that the properties of the ß-relaxation are mainly determined by the interaction between the largest solvent element, La, and the smallest element, Ni. From our data, it is further deduced that La and Ni have high mobility in the MGs, and this explains why the ß-relaxation in this La-based MGs is prominent and well resolved from the α-relaxation as opposed to Pd- and Zr-based MGs where the solvent and largest atoms, Pd and Zr, are the least mobile.

Tensile plasticity in metallic glasses with pronounced ß relaxations.

Metallic glasses are commonly brittle, as they generally fail catastrophically under uniaxial tension. Here we show pronounced macroscopic tensile plasticity achieved in a La-based metallic glass which possesses strong ß relaxations and nanoscale heterogeneous structures. We demonstrate that the ß relaxation is closely correlated with the activation of the structural units of plastic deformations and global plasticity, and the transition from brittle to ductile in tension and the activation of the ß relaxations follow a similar time-temperature scaling relationship. The results have implications for understanding the mechanisms of plastic deformation and structural origin of ß relaxations as well as for solving the brittleness in metallic glasses.

Unusually thick shear-softening surface of micrometer-size metallic glasses.

The surface of glass is crucial for understanding many fundamental processes in glassy solids. A common notion is that a glass surface is a thin layer with liquid-like atomic dynamics and a thickness of a few tens of nanometers. Here, we measured the shear modulus at the surface of both millimeter-size and micrometer-size metallic glasses (MGs) through high-sensitivity torsion techniques. We found a pronounced shear-modulus softening at the surface of MGs. Compared with the bulk, the maximum decrease in the surface shear modulus (G) for the micro-scale MGs reaches ~27%, which is close to the decrease in the G upon glass transition, yet it still behaves solid-like. Strikingly, the surface thickness estimated from the shear-modulus softening is at least 400 nm, which is approximately one order of magnitude larger than that revealed from the glass dynamics. The unusually thick surface is also confirmed by measurements using X-ray nano-computed tomography, and this may account for the brittle-to-ductile transition of the MGs with size reductions. The unique and unusual properties at the surface of the micrometer-size MGs are physically related to the negative pressure effect during the thermoplastic formation process, which can dramatically reduce the density of the proximate surface region in the supercooled liquid state.

Plasticity of ductile metallic glasses: a self-organized critical state.

We report a close correlation between the dynamic behavior of serrated flow and the plasticity in metallic glasses (MGs) and show that the plastic deformation of ductile MGs can evolve into a self-organized critical state characterized by the power-law distribution of shear avalanches. A stick-slip model considering the interaction of multiple shear bands is presented to reveal complex scale-free intermittent shear-band motions in ductile MGs and quantitatively reproduce the experimental observations. Our studies have implications for understanding the precise plastic deformation mechanism of MGs.

Metallic Glacial Glass Formation by a First-Order Liquid-Liquid Transition.

The glacial phase, with an apparently glassy structure, can be formed by a first-order transition in some molecular-glass-forming supercooled liquids. Here we report the formation of metallic glacial glass (MGG) from the precursor of a rare-earth-element-based metallic glass via the first-order phase transition in its supercooled liquid. The excellent glass-forming ability of the precursor ensures the MGG to be successfully fabricated into bulk samples (with a minimal critical diameter exceeding 3 mm). Distinct enthalpy, structure, and property changes are detected between MGG and metallic glass, and the reversed "melting-like" transition from the glacial phase to the supercooled liquid is observed in fast differential scanning calorimetry. The kinetics of MGG formation is reflected by a continuous heating transformation diagram, with the phase transition pathways measured at different heating rates taken into account. The finding supports the scenario of liquid-liquid transition in metallic-glass-forming liquids.

Liquid-like behaviours of metallic glassy nanoparticles at room temperature.

Direct atomic-scale observations and measurements on dynamics of amorphous metallic nanoparticles (a-NPs) are challenging owing to the insufficient consciousness to their striking characterizations and the difficulties in technological approaches. In this study, we observe coalescence process of the a-NPs at atomic scale. We measure the viscosity of the a-NPs through the particles coalescence by in situ method. We find that the a-NPs have fast dynamics, and the viscosity of the a-NPs exhibits a power law relationship with size of the a-NPs. The a-NPs with sizes smaller than 3 nm are in a supercooled liquid state and exhibit liquid-like behaviours with a decreased viscosity by four orders of magnitude lower than that of bulk glasses. These results reveal the intrinsic flow characteristics of glasses in low demension, and pave a way to understand the liquid-like behaviours of low dimension glass, and are also of key interest to develop size-controlled nanodevices.

Schoepfin A, B, C: three new chalcone C-glycosides from Schoepfia chinensis.

Three new chalcone C-glycosides named schoepfin A, B, C (1-3), together with three known compounds 4,2',4'-trihydroxy-3'-C-beta-D-glucosylchalcone (4), nothofagin (5) and hemiphloin (6) were isolated from ethanolic extract of the bark of Schoepfia chinensis Gardn. et Champ (Olacaceae). Their structures were determined mainly by spectroscopic techniques including 2D-NMR (HMBC, HMQC) and MS experiments.

Shear-band affected zone revealed by magnetic domains in a ferromagnetic metallic glass.

Plastic deformation of metallic glasses (MGs) has long been considered to be confined to nanoscale shear bands, but recently an affected zone around the shear band was found. Yet, due to technical limitations, the shear-band affected zone (SBAZ), which is critical for understanding shear banding and design of ductile MGs, has yet to be precisely identified. Here, by using magnetic domains as a probe with sufficiently high sensitivity and spatial resolution, we unveil the structure of SBAZs in detail. We demonstrate that shear banding is accompanied by a micrometer-scale SBAZ with a gradient in the strain field, and multiple shear bands interact through the superimposition of SBAZs. There also exists an ultra-long-range gradual elastic stress field extending hundreds of micrometers away from the shear band. Our findings provide a comprehensive picture on shear banding and are important for elucidating the micro-mechanisms of plastic deformation in glasses.