Network-Configurations of Dynamic Friction Patterns

The complex configurations of dynamic friction patterns-regarding real time contact areas- are transformed into appropriate networks. With this transformation of a system to network space, many properties can be inferred about the structure and dynamics of the system. Here, we analyze the dynamics of static friction, i.e. nucleation processes, with respect to "friction networks". We show that networks can successfully capture the crack-like shear ruptures and possible corresponding acoustic features. We found that the fraction of triangles remarkably scales with the detachment fronts. There is a universal power law between nodes' degree and motifs frequency (for triangles, it reads T(k)\proptok{\beta} ({\beta} \approx2\pm0.4)). We confirmed the obtained universality in aperture-based friction networks. Based on the achieved results, we extracted a possible friction law in terms of network parameters and compared it with the rate and state friction laws. In particular, the evolutions of loops are scaled with power law, indicating the aggregation of cycles around hub nodes. Also, the transition to slow rupture is scaled with the fast variation of local heterogeneity. Furthermore, the motif distributions and modularity space of networks -in terms of withinmodule degree and participation coefficient-show non-uniform general trends, indicating a universal aspect of energy flow in shear ruptures

Topological Complexity of Frictional Interfaces: Friction Networks

Through research conducted in this study, a network approach to the correlation patterns of void spaces in rough fractures (crack type II) was developed. We characterized friction networks with several networks characteristics. The correlation among network properties with the fracture permeability is the result of friction networks. The revealed hubs in the complex aperture networks confirmed the importance of highly correlated groups to conduct the highlighted features of the dynamical aperture field. We found that there is a universal power law between the nodes' degree and motifs frequency (for triangles it reads T(k)\proptok{\beta} ({\beta} \approx2\pm0.3)). The investigation of localization effects on eigenvectors shows a remarkable difference in parallel and perpendicular aperture patches. Furthermore, we estimate the rate of stored energy in asperities so that we found that the rate of radiated energy is higher in parallel friction networks than it is in transverse directions. The final part of our research highlights 4 point sub-graph distribution and its correlation with fluid flow. For shear rupture, we observed a similar trend in sub-graph distribution, resulting from parallel and transversal aperture profiles (a superfamily phenomenon)

Magnetic properties of geometrically frustrated SrGd2O4

A study of the magnetic properties of the frustrated rare earth oxide SrGd2O4 has been completed using bulk property measurements of magnetization, susceptibility and specific heat on single crystal samples. Two zero-field phase transitions have been identified at 2.73 and 0.48 K. For the field, H, applied along the a and b axes, a single boundary is identified that delineates the transition from a low field, low temperature magnetically ordered regime to a high field, high temperature paramagnetic phase. Several field-induced transitions, however, have been observed with H || c. The measurements have been used to map out the magnetic phase diagram of SrGd2O4, suggesting that it is a complex system with several competing magnetic interactions. The low-temperature magnetic behavior of SrGd2O4 is very different compared to the other SrLn2O4 (Ln = Lanthanide) compounds, even though all of the SrLn2O4 compounds are isostructural, with the magnetic ions forming a low-dimensional lattice of zigzag chains that run along the c axis. The differences are likely to be due to the fact that in the ground state Gd3+ has zero orbital angular momentum and therefore the spin-orbit interactions, which are crucial for other SrLn2O4 compounds, can largely be neglected. Instead, given the relatively short Gd3+-Gd3+ distances in SrGd2O4, dipolar interactions must be taken into account for this antiferromagnet alongside the Heisenberg exchange terms.Comment: 10 pages, 9 figure

A millimeter wavelength interferometer spectrometer Final report

Millimeter wavelength interferometer spectrometer for geological measurement

Experimental and numerical studies of ferritic stainless steel tubular cross sections under combined compression and bending

An experimental and numerical study of ferritic stainless steel tubular cross sections under combined loading is presented in this paper. Two square hollow section (SHS) sizes—SHS 40×40×240×40×2 and SHS 50×50×250×50×2 made of Grade EN 1.4509 (AISI 441) stainless steel—were considered in the experimental program, which included 2 concentrically loaded stub column tests, 2 four-point bending tests, and 14 eccentrically loaded stub column tests. In parallel with the experimental investigation, a finite-element (FE) study was also conducted. Following validation of the FE models against the test results, parametric analyses were carried out to generate further structural performance data. The experimental and numerical results were analyzed and compared with the design strengths predicted by the current European stainless steel design code EN 1993-1-4 and American stainless steel design specification SEI/ASCE-8. The comparisons revealed that the codified capacity predictions for ferritic stainless steel cross sections under combined loading are unduly conservative. The deformation-based continuous strength method (CSM) has been extended to cover the case of combined loading. The applicability of CSM to the design of ferritic stainless steel cross sections under combined loading was also evaluated. The CSM was shown to offer substantial improvements in design efficiency over existing codified methods. Finally, the reliability of the proposals was confirmed by means of statistical analyses according to both the SEI/ASCE-8 requirements and those of EN 1990

African wild ungulates compete with or facilitate cattle depending on season

Savanna ecosystems are vital for both economic and biodiversity values. In savannas worldwide, management decisions are based on the concept that wildlife and livestock compete for grassland resources[1-4], yet there are virtually no experimental data to support this assumption[1]. Specifically, the critical assessment of whether or not wild ungulates alter livestock performance (e.g., weight gain, reproduction or survival) has rarely been carried out, although diminished performance is an essential prerequisite for inferring competition[1]. Here we use a large-scale experiment in a semi-arid savanna in Kenya to show that wild ungulates do depress cattle performance (weight gain) during the dry season, indicating a competitive effect, but enhance cattle performance during the wet season, signifying facilitation. This is the first experimental demonstration of either competitive or facilitative effects of an assemblage of native ungulates on domestic livestock in a savanna ecosystem, and a unique demonstration of a rainfall-dependent shift in competition-facilitation balance within any herbivore guild. These results are critical for better understanding and management of wildlife-livestock coexistence in savanna ecosystems globally, and especially in the African savanna biome which crucially hosts the last remnants of an intact large herbivore fauna

An Extremal Chiral Primary Three-Point Function at Two-loops in ABJ(M)

archiveprefix: arXiv primaryclass: hep-th reportnumber: QMUL-PH-14-23 slaccitation: %%CITATION = ARXIV:1411.0626;%%archiveprefix: arXiv primaryclass: hep-th reportnumber: QMUL-PH-14-23 slaccitation: %%CITATION = ARXIV:1411.0626;%%archiveprefix: arXiv primaryclass: hep-th reportnumber: QMUL-PH-14-23 slaccitation: %%CITATION = ARXIV:1411.0626;%