Anisotropic generalization of Buchdahl bound for specific stellar models

Anisotropy is one factor that appears to be significantly important in the studies of relativistic compact stars. In this paper, we make a generalization of the Buchdahl limit by incorporating an anisotropic effect for a selected class of exact solutions describing anisotropic stellar objects. In the isotropic case of a homogeneous distribution, we regain the Buchdahl limit $$2M/R \le 8/9$$ 2 M / R ≤ 8 / 9 . Our investigation shows a direct link between the maximum allowed compactness and pressure anisotropy vi-a-vis geometry of the associated 3-space.

Linking static and dynamic mechanical properties for metamorphic rocks from Austria including their anisotropic effect

The derivation of geomechanical properties from petrophysical/geophysical data is not only of great importance in the oil industry but also in mining, geothermal projects and tunnelling, for reduction of costs and to improve security. For the oil industry and geothermal sector, it is mainly important for drilling rate and the stability of the borehole and, as a result, the economic factor. A key issue is that geomechanical properties, which can support a better planning of a project, cannot be measured in the borehole or on the surface directly. In this study, the focus is put on anisotropic effects on the correlation between static and dynamic properties, which is neglected in most studies but important because values can vary extremely. Therefore, measurements in the geotechnical laboratory of compressional and shear wave velocity during uniaxial compression strength test were taken. Additionally, typical properties like bulk and grain density as well as porosity were determined too. Different samples (carbonate–silica schist, marble and phyllite) from the "Zentrum am Berg"-research tunnelling centre at the "Erzberg" in Austria were used. Shown are correlations between uniaxial compression strength and compressional wave velocity as well as for static and dynamic Young’s modulus including their anisotropic effect. The results are promising and provide an opportunity for further applications on log data.

Facile chemical strategy to synthesize Ag@polypyrrole microarrays and investigating its anisotropic effect on polymer conductivity

A facile chemical approach was developed to fabricate microarrays (MAs) of Ag@polypyrrole nanocables (NCs). The strategy involved crosslinking the NCs by tetraethoxy silane (TEOS) under continuous pulse sonication without using a substrate. The material was characterized by scanning electron microscope (SEM) coupled with EDX, which revealed the longitudinal interconnections within the nanocables and creating unidirectional alignment in the form of MAs. FT-IR and Raman spectroscopy was employed to characterize the encapsulating polymer as polypyrrole (ppy) around Ag nanowires (NWs). The microarrays produced red shift in surface plasmon resonance (SPR) of Ag NWs, and drastically improved the thermal stability and conductivity of encasing ppy. It has imparted anisotropic conductivity effect on ppy which resulted in sharp decrease in resistivity from 8.35 × 1010 Ω to 2.449 Ω, when NCs were isolated and crosslinked into MAs form, respectively. The drastic decrease in resistivity of ppy was due to the anisotropic effect produced by the MAs format of NWs.