Self-Doping and the Mott-Kondo Scenario for Infinite-Layer Nickelate Superconductors

We give a brief review of the Mott-Kondo scenario and its consequence in the recently-discovered infinite-layer nickelate superconductors. We argue that the parent state is a self-doped Mott insulator and propose an effective t- J-K model to account for its low-energy properties. At small doping, the model describes a low carrier density Kondo system with incoherent Kondo scattering at finite temperatures, in good agreement with experimental observation of the logarithmic temperature dependence of electric resistivity. Upon increasing Sr doping, the model predicts a breakdown of the Kondo effect, which provides a potential explanation of the non-Fermi liquid behavior of the electric resistivity with a power law scaling over a wide range of the temperature. Unconventional superconductivity is shown to undergo a transition from nodeless (d+is)-wave to nodal d-wave near the critical doping due to competition of the Kondo and Heisenberg superexchange interactions. The presence of different pairing symmetry may be supported by recent tunneling measurements.

Assessment of landslides in Bosnia & Herzegovina and Serbia: A Geoscientists without Borders project

A severe storm caused floods and landslides in the Balkan region in May 2014. In response to the disaster, geophysical and geotechnical surveys were organized as a Geoscientists without Borders® (GwB) project of SEG. It took place in eight landslide prone areas in Serbia and Bosnia Herzegovina in three phases in 2015 and 2016. The seismic and electric resistivity surveys were conducted and the results were interpreted in conjunction with the geotechnical inspection. The surveys identified the size of a potential landslide layer by S-wave velocity distribution and particular high-risk locations by electric resistivity anomalies. This interpretation enhanced the geotechnical observation. From the result, several countermeasures were recommended to suit the budgetary restrictions of local governments. Among them, the survey results in the Lopare locality are presented as an example. The project was organized by the Association of Geophysicists and Environmentalists of Serbia (AGES) involving many scientists, engineers, students, government staff and local communities. As well as technical achievements, significance of the project includes: providing students with opportunities to have practical experience of geophysical surveys and to learn outside the classroom; bringing together the participants from different racial, political, religious and educational backgrounds. All were made aware of the importance of humanitarian expert work. We assessed the effectiveness of the GwB project using the guidelines of Organization for Economic Co-operation and Development, Development Assistance Committee (OECD-DAC). One of the important outcomes of the assessment is that such a volunteer geoscientific survey cannot stand alone. It is more effective if incorporated in the overall recovery and prevention programs.

Properties of Fibre-Reinforced High-Strength Concrete with Nano-Silica and Silica Fume

This study intends to assess the influence of steel fibres (SF) and polypropylene fibres (PPF) on the hardened and fresh state properties of high-strength concrete (HSC). For this purpose, 99 concrete mixes were designed and applied. SF and PPF were used at six-volume replacement contents of 0%, 0.1%, 0.2%, 0.3%, 0.4% and 0.5%. Moreover, nano-silica (NS) was used at three contents, 0%, 1% and 2%, and silica fume powder (SP) was also used at three weight ratios (0%, 5% and 10%). The slump, compressive and tensile strength, elasticity modulus, water absorption and the electric resistivity of concrete specimens were examined. The results showed that using 1% NS and 10% SP together with 0.5% PPF improved the compressive strength of HSC by about 123%; however, the effect of SF on tensile strength is more significant and adding 0.5% SF with both 2% NS and 10% SP increased the tensile strength by 104%. Moreover, increasing the SF content reduces the electric resistivity while using PPF improves this property especially when 1% NS was employed, and it was enhanced by about 68% when 0.5% SF and 1% NS were utilized with 10% SP.