Order-disorder transitions in a sheared many body system

Motivated by experiments on sheared suspensions that show a transition between ordered and disordered phases, we here study the long-time behavior of a sheared and overdamped 2-d system of particles interacting by repulsive forces. As a function of interaction strength and shear rate we find transitions between phases with vanishing and large single-particle diffusion. In the phases with vanishing single-particle diffusion, the system evolves towards regular lattices, usually on very slow time scales. Different lattices can be approached, depending on interaction strength and forcing amplitude. The disordered state appears in parameter regions where the regular lattices are unstable. Correlation functions between the particles reveal the formation of shear bands. In contrast to single particle densities, the spatially resolved two-particle correlation functions vary with time and allow to determine the phase within a period. As in the case of the suspensions, motion in the state with low diffusivity is essentially reversible, whereas in the state with strong diffusion it is not.Comment: 12 pages, 13 figures; Supplemental Movies: https://youtu.be/oFcrWo9Vs6E, https://youtu.be/tcowb7o05JQ, https://youtu.be/GkEUwycn7V4, https://youtu.be/k-XCo8CWFU

Rigidity, Secondary Structure, and the Universality of the Boson Peak in Proteins

AbstractComplementary neutron- and light-scattering results on nine proteins and amino acids reveal the role of rigidity and secondary structure in determining the time- and lengthscales of low-frequency collective vibrational dynamics in proteins. These dynamics manifest in a spectral feature, known as the boson peak (BP), which is common to all disordered materials. We demonstrate that BP position scales systematically with structural motifs, reflecting local rigidity: disordered proteins appear softer than α-helical proteins; which are softer than β-sheet proteins. Our analysis also reveals a universal spectral shape of the BP in proteins and amino acid mixtures; superimposable on the shape observed in typical glasses. Uniformity in the underlying physical mechanism, independent of the specific chemical composition, connects the BP vibrations to nanometer-scale heterogeneities, providing an experimental benchmark for coarse-grained simulations, structure/rigidity relationships, and engineering of proteins for novel applications

Stripe order in the underdoped region of the two-dimensional Hubbard model

Competing inhomogeneous orders are a central feature of correlated electron materials including the high-temperature superconductors. The two- dimensional Hubbard model serves as the canonical microscopic physical model for such systems. Multiple orders have been proposed in the underdoped part of the phase diagram, which corresponds to a regime of maximum numerical difficulty. By combining the latest numerical methods in exhaustive simulations, we uncover the ordering in the underdoped ground state. We find a stripe order that has a highly compressible wavelength on an energy scale of a few Kelvin, with wavelength fluctuations coupled to pairing order. The favored filled stripe order is different from that seen in real materials. Our results demonstrate the power of modern numerical methods to solve microscopic models even in challenging settings

The main geological factors influencing on formation of indices of coal quality (on the example of the coal deposit "Neryungrinskoye")

Genetic and epigenetic factors influencing on formation of a coal bed (its characteristics expressing by means of morphology, petrographic composition, degree of reducing, metamorphism, oxidation, and dislocation, physical properties and indices of coal quality) are considered. The main task of this research consisted in establishing of the significant factors influencing of the coal bed quality indices to a greater extent. Solution of the set task from positions of a system approach at study of rock massifs consisting in revealing and studying of many interconnected elements and estimation of their influence by means of alternate normalization of the main bounds is shown. The study was carry out in conditions of the bed «Moshny» of the coal deposit «Neryngrinskoye» of the Southern-Yakutia basin. The experimental data were treated with use of the correlation-regression methods. Results of researches allow to use geological information and geophysical methods for operative planning of geologic prospecting process and mining works in more total way

Overcoming High Energy Backgrounds at Pulsed Spallation Sources

Instrument backgrounds at neutron scattering facilities directly affect the quality and the efficiency of the scientific measurements that users perform. Part of the background at pulsed spallation neutron sources is caused by, and time-correlated with, the emission of high energy particles when the proton beam strikes the spallation target. This prompt pulse ultimately produces a signal, which can be highly problematic for a subset of instruments and measurements due to the time-correlated properties, and different to that from reactor sources. Measurements of this background have been made at both SNS (ORNL, Oak Ridge, TN, USA) and SINQ (PSI, Villigen, Switzerland). The background levels were generally found to be low compared to natural background. However, very low intensities of high-energy particles have been found to be detrimental to instrument performance in some conditions. Given that instrument performance is typically characterised by S/N, improvements in backgrounds can both improve instrument performance whilst at the same time delivering significant cost savings. A systematic holistic approach is suggested in this contribution to increase the effectiveness of this. Instrument performance should subsequently benefit.Comment: 12 pages, 8 figures. Proceedings of ICANS XXI (International Collaboration on Advanced Neutron Sources), Mito, Japan. 201