Triaxial compression tests on a crushable sand in dry and wet conditions

A calcareous sand from the Persian Gulf is subjected to a series of dry and fully drained saturated triaxial shear tests. The samples are prepared at relative densities of 65% and either left dry or saturated. They are consolidated to confining pressures ranging from 50 to 750 kPa, and sheared until shear strains of 20%. It is shown that the stress-strain and strength characteristics of crushable sand are significantly affected by the presence of water. During shearing of wet samples, there is less dilation, the peak is postponed and a lower shear strength is reached compared to dry samples. Crushability is assessed by comparing the granulometry before and after the triaxial tests. While both dry and wet samples show breakage, the wet sand is consistently more crushable. It is stated that the higher crushability of the wet sand suppresses its dilation during shearing

Faster Methods for Contracting Infinite 2D Tensor Networks

We revisit the corner transfer matrix renormalization group (CTMRG) method of Nishino and Okunishi for contracting two-dimensional (2D) tensor networks and demonstrate that its performance can be substantially improved by determining the tensors using an eigenvalue solver as opposed to the power method used in CTMRG. We also generalize the variational uniform matrix product state (VUMPS) ansatz for diagonalizing 1D quantum Hamiltonians to the case of 2D transfer matrices and discuss similarities with the corner methods. These two new algorithms will be crucial to improving the performance of variational infinite projected entangled pair state (PEPS) methods.Comment: 20 pages, 5 figures, V. Zauner-Stauber previously also published under the name V. Zaune

Topological nature of spinons and holons: Elementary excitations from matrix product states with conserved symmetries

We develop variational matrix product state (MPS) methods with symmetries to determine dispersion relations of one dimensional quantum lattices as a function of momentum and preset quantum number. We test our methods on the XXZ spin chain, the Hubbard model and a non-integrable extended Hubbard model, and determine the excitation spectra with a precision similar to the one of the ground state. The formulation in terms of quantum numbers makes the topological nature of spinons and holons very explicit. In addition, the method also enables an easy and efficient direct calculation of the necessary magnetic field or chemical potential required for a certain ground state magnetization or particle density.Comment: 13 pages, 4 pages appendix, 8 figure

Thermal States as Convex Combinations of Matrix Product States

We study thermal states of strongly interacting quantum spin chains and prove that those can be represented in terms of convex combinations of matrix product states. Apart from revealing new features of the entanglement structure of Gibbs states our results provide a theoretical justification for the use of White's algorithm of minimally entangled typical thermal states. Furthermore, we shed new light on time dependent matrix product state algorithms which yield hydrodynamical descriptions of the underlying dynamics.Comment: v3: 10 pages, 2 figures, final published versio

Deconstructing the Subject Condition in terms of cumulative constraint violation

Chomsky (1973) attributes the island status of nominal subjects to the Subject Condition, a constraint specific to subjects. English and Spanish are interesting languages for the comparative study of extraction from subjects, because subjects in English are predominantly preverbal, whereas in Spanish they can be either preverbal or postverbal. In this paper we argue that the islandhood of subject DPs in both English and Spanish is not categorical. The degradation associated with extraction from subjects must be attributed to the interplay of a range of more general constraints which are not specific to subjects. We argue that the interaction of these constraints has a cumulative effect whereby the more constraints that are violated, the higher the degree of degradation that results. We also argue that some speakers have a greater tolerance for constraint violations than others, which would account for widespread inter-speaker judgment variability

Transfer Matrices and Excitations with Matrix Product States

We investigate the relation between static correlation functions in the ground state of local quantum many-body Hamiltonians and the dispersion relations of the corresponding low energy excitations using the formalism of tensor network states. In particular, we show that the Matrix Product State Transfer Matrix (MPS-TM) - a central object in the computation of static correlation functions - provides important information about the location and magnitude of the minima of the low energy dispersion relation(s) and present supporting numerical data for one-dimensional lattice and continuum models as well as two-dimensional lattice models on a cylinder. We elaborate on the peculiar structure of the MPS-TM's eigenspectrum and give several arguments for the close relation between the structure of the low energy spectrum of the system and the form of static correlation functions. Finally, we discuss how the MPS-TM connects to the exact Quantum Transfer Matrix (QTM) of the model at zero temperature. We present a renormalization group argument for obtaining finite bond dimension approximations of MPS, which allows to reinterpret variational MPS techniques (such as the Density Matrix Renormalization Group) as an application of Wilson's Numerical Renormalization Group along the virtual (imaginary time) dimension of the system.Comment: 39 pages (+8 pages appendix), 14 figure

Cow responses and evolution of the rumen bacterial and methanogen community following a complete rumen content transfer

Understanding the rumen microbial ecosystem requires the identification of factors that influence the community structure, such as nutrition, physiological condition of the host and host-microbiome interactions. The objective of the current study was to describe the rumen microbial communities before, during and after a complete rumen content transfer. The rumen contents of one donor cow were removed completely and used as inoculum for the emptied rumen of the donor itself and three acceptor cows under identical physiological and nutritional conditions. Temporal changes in microbiome composition and rumen function were analysed for each of four cows over a period of 6 weeks. Shortly after transfer, the cows showed different responses to perturbation of their rumen content. Feed intake depression in the first 2 weeks after transfer resulted in short-term changes in milk production, methane emission, fatty acid composition and rumen bacterial community composition. These effects were more pronounced in two cows, whose microbiome composition showed reduced diversity. The fermentation metrics and microbiome diversity of the other two cows were not affected. Their rumen bacterial community initially resembled the composition of the donor but evolved to a new community profile that resembled neither the donor nor their original composition. Descriptive data presented in the current paper show that the rumen bacterial community composition can quickly recover from a reduction in microbiome diversity after a severe perturbation. In contrast to the bacteria, methanogenic communities were more stable over time and unaffected by stress or host effects