The Superconducting Critical Temperature

Two principles govern the critical temperature for superconducting transitions: (1) intrinsic strength of the pair coupling and (2) the effect of the many-body environments on the efficiency of that coupling. Most discussions take into account only the former, but we argue that the properties of unconventional superconductors are governed more often by the latter, through dynamical symmetry relating to normal and superconducting states. Differentiating these effects is essential to charting a path to the highest-temperature superconductors.

The interplay between recycled and primordial heterogeneities: predicting Earth's mantle dynamics via numerical modeling

<p>According to geochemical and geophysical observations, Earth's lower mantle appears to be strikingly heterogeneous in composition. An accurate interpretation of these findings is critical to constrain Earth's bulk composition and long-term evolution. To this end, two main models have gained traction, each reflecting a different style of chemical heterogeneity preservation: the 'marble cake' and 'plum pudding' mantle. In the former, heterogeneity is preserved in the form of narrow streaks of recycled oceanic lithosphere, stretched and stirred throughout the mantle by convection. In the latter, domains of intrinsically strong, primordial material (enriched in the lower-mantle mineral bridgmanite) may resist convective entrainment and survive as coherent blobs in the mid mantle. Microscopic scale processes certainly affect macroscopic properties of mantle materials and thus reverberate on large-scale mantle dynamics. A cross-disciplinary effort is therefore needed to constrain present-day Earth structure, yet countless variables remain to be explored. Among previous geodynamic studies, for instance, only few have attempted to address how the viscosity and density of recycled and primordial materials affect their mutual mixing and interaction in the mantle.</p><p>Here, we apply the finite-volume code <strong>STAGYY</strong> to model thermochemical convection of the mantle in a 2D spherical-annulus geometry. All models are initialized with a lower, primordial layer and an upper, pyrolitic layer (i.e., a mechanical mixture of basalt and harzburgite), as is motivated by magma-ocean solidification studies. We explore the effects of material properties on the style of mantle convection and heterogeneity preservation. These parameters include (i) the intrinsic strength of basalt (viscosity), (ii) the intrinsic density of basalt, and (iii) the intrinsic strength of the primordial material.</p><p>Our preliminary models predict a range of different mantle mixing styles. A 'marble cake'-like regime is observed for low-viscosity primordial material (~30 times weaker than the ambient mantle), with recycled oceanic lithosphere preserved as streaks and thermochemical piles accumulating near the core-mantle boundary. Conversely, 'plum pudding' primordial blobs are also preserved when the primordial material is relatively strong, in addition to the 'marble cake' heterogeneities mentioned above. Most notably, however, the rheology and the density anomaly of basalt affect the appearance of both recycled and primordial heterogeneities. In particular, they control the stability, size and geometry of thermochemical piles, the enhancement of basaltic streaks in the mantle transition zone, and they influence the style of primordial material preservation. These results indicate the important control that the physical properties of mantle constituents exert on the style of mantle convection and mixing over geologic time. Our numerical models offer fresh insights into these processes and may advance our understanding of the composition and structure of Earth's lower mantle.</p>

Intrinsic strength and the structure of glass

Intrinsic strength is the strength of a glass without extrinsic flaws. Knowledge of the composition dependence of the intrinsic strength is important both technologically for the development of high strength glass compositions and theoretically as it may provide important structural information. Intrinsic strength is easy to define but difficult to measure experimentally. In this paper we discuss intrinsic (σ*) strength measured in normal laboratory conditions as well as the inert intrinsic (σ0*) strength. We define these terms in a rigorous manner and indicate how to gauge if they have been measured by developing a set of criteria. Based on these criteria, we tabulate those values of intrinsic strengths that have been measured to date.

Turkey’s response to COVID-19 in terms of mental health

Coronavirus disease (also known as COVID-19) continues to spread throughout the world. In Turkey, which has a strong health system, most hospitals have been turned into pandemic hospitals, elective procedures have been postponed, and doctors have been reassigned to treat COVID-19. Efforts to limit spread of COVID-19 have been effective in reducing the spread of COVID-19. Behind this success was not only the intrinsic strength of the health system but also the strict changes in everyday life wrought by the crisis. It is an inescapable fact that these new measures, such as the imposition of curfew and lockdown, have had a significant effect on the mental health of the general population. Anxiety caused by COVID-19 has spread to the mental state of everyone. Although coronavirus-related diseases will end soon, it is predicted that serious psychiatric disorders will be a lasting consequence of the pandemic. Despite the many negatives brought by COVID-19, it has led to a positive unity between the public and healthcare professionals, and in spite of significant risks to their own health, healthcare workers have risen to the challenge of COVID-19.

Increasing Surface Hardness of S304 Stainless Steel by High Quality Graphene Grown by Chemical Vapor Deposition

Stainless steel is widely utilized due to its higher corrosion resistance and gloss than ordinary steels. However, the applications of stainless steel are still limited because of its low surface hardness. Graphene is a superb material, which has an intrinsic strength of 130 GPa. In this report, the growth of high quality graphene on S304 stainless steel by chemical vapor deposition using acetylene gas as a carbon source is demonstrated. The surface hardness of stainless steel after growing high quality graphene is investigated by nanoindentation technique. High quality graphene can increase the surface hardness of stainless steel from 1.54 GPa to 10.08 GPa. Moreover, the effect of graphene quality on the surface hardness of S304 stainless steel is studied. High quality graphene grown by CVD using acetylene gas as a carbon source can increase the surface hardness of stainless steel about two times more than low quality graphene grown by using methane gas.

In Situ Assessment of Intrinsic Strength of X-I⋯OA-Type Halogen Bonds in Molecular Crystals with Periodic Local Vibrational Mode Theory

Periodic local vibrational modes were calculated with the rev-vdW-DF2 density functional to quantify the intrinsic strength of the X-I⋯OA-type halogen bonding (X = I or Cl; OA: carbonyl, ether and N-oxide groups) in 32 model systems originating from 20 molecular crystals. We found that the halogen bonding between the donor dihalogen X-I and the wide collection of acceptor molecules OA features considerable variations of the local stretching force constants (0.1–0.8 mdyn/Å) for I⋯O halogen bonds, demonstrating its powerful tunability in bond strength. Strong correlations between bond length and local stretching force constant were observed in crystals for both the donor X-I bonds and I⋯O halogen bonds, extending for the first time the generalized Badger’s rule to crystals. It is demonstrated that the halogen atom X controlling the electrostatic attraction between the σ -hole on atom I and the acceptor atom O dominates the intrinsic strength of I⋯O halogen bonds. Different oxygen-containing acceptor molecules OA and even subtle changes induced by substituents can tweak the n → σ ∗ (X-I) charge transfer character, which is the second important factor determining the I⋯O bond strength. In addition, the presence of the second halogen bond with atom X of the donor X-I bond in crystals can substantially weaken the target I⋯O halogen bond. In summary, this study performing the in situ measurement of halogen bonding strength in crystalline structures demonstrates the vast potential of the periodic local vibrational mode theory for characterizing and understanding non-covalent interactions in materials.

Characterizing the Intrinsic Strength (Fatigue Threshold) of Natural Rubber/Butadiene Rubber Blends

ABSTRACT Tires require rubber compounds capable of enduring more than 108 deformation cycles without developing cracks. One strategy for evaluating candidate compounds is to measure the intrinsic strength, which is also known as the fatigue threshold or endurance limit. The intrinsic strength is the residual strength remaining in the material after the strength-enhancing effects of energy dissipation in crack tip fields are removed. If loads stay always below the intrinsic strength (taking proper account of the possibility that the intrinsic strength may degrade with aging), then cracks cannot grow. Using the cutting protocol proposed originally by Lake and Yeoh, as implemented on a commercial intrinsic strength analyzer, the intrinsic strength is determined for a series of carbon black (CB) reinforced blends of natural rubber (NR) and butadiene rubber (BR) typical of tire applications. The intrinsic strength benefits of the blends over the neat NR and BR compounds are only observed after aging at temperatures in the range from 50 to 70 °C, thus providing fresh insights into the widespread durability success of CB-filled NR/BR blends in tire sidewall compounds and commercial truck tire treads.

Atomic Structure and Mechanical Properties of Twisted Bilayer Graphene

We studied the atomic structure and mechanical properties of twisted bilayer graphene with a different twist angle using molecular dynamic simulations. The two layers are corrugated after energy minimization. We found two different modes of corrugation. The mechanical properties are tested both in-plane and perpendicular to the plane. The in-plane properties are dominated by the orientation of graphene. The perpendicular properties depend on the twist angle, as the larger the twist angle, the higher the intrinsic strength.