The influence of state on the capacity of driven piles in sands

The prime objective of the thesis was to study the influence of state on the capacity of driven piles in sand. The work was prompted by findings of recent laboratory based research on the mechanics of granular soils (Coop & Lee, 1993 and Jovicic & Coop, 1997) which showed that, as for clays, a principal controlling factor of soil behaviour is the stress-volume state. The work started in November 1996 and was funded buy the EPSRC under contract GR/L16590. Centrifuge testing was used to investigate the behaviour of driven piles in sands. A new actuator and strongbox package were designed and constructed taking full advantage of the centrifuge facilities. A fully instrumented model pile was developed, which consisted of eleven segments and allowed five independent measurements of shaft friction, four of radial stress and one of end bearing to be taken during installation. The pile was jacked into samples of two sands of varying densities at accelerations of between 50-200g, simulating piles of up to 70 min length and 3.2 m in diameter. The two sands used in the investigation were a carbonate sand and a quartz sand, chosen for the diversity of their geological origins and behaviour. A series of triaxial tests was conducted in order to characterise the behaviour of each sand, and in particular to locate precisely their critical state lines in stress-volume space. The centrifuge model tests showed that neither the end bearing nor the shaft friction could be adequately predicted using methods based on relative density of the sand such as APIRP2A (1993), but that the controlling factor for both was the state of the soil relative to the location of the critical state line, which should be quantified not only by the density of the soil, but also the effective stress level. The radial stress was found to be highest approximately seven pile diameters above the pile tip and not at the pile tip as assumed in recent design methods (e. g. Randolph et al., 1994 and Jardine & Chow, 1996). The friction angles mobilised on the model pile were found to be significantly lower than those that were measured by means of interface shear box tests, and it was found that the correct friction angle could only be measured by interface ring shear tests taken to very large displacements. An examination of the literature showed clearly that available field data support the new framework, although the data were both very scattered and very limited in extent, particularly because even the most extensive field tests rarely included even the basic laboratory tests required to apply the new method of analysis. The work therefore highlights severe limitations with many current pile design methods for piles in sands and suggests how new methods should be based on correct quantification of state

Characterization of [3H][^3H]Phenobarbital Binding to Rat Brain Membranes

The binding of $[^3H]$phenobarbital to rat brain membranes was studied in order to determine its characteristics and specificity. The binding reaction was rapid and occurred at sites of low affinity. $(K_d = 700 μM)$ and very high density $(B_{max} = 2.7 nmoll/mg protein)$. It was unaffected by temperature changes from O°C to 95°C and was maximal at pH 5. Detergents in low concentrations markedly decreased the binding, apparently without solubilizing the binding sites. It is concluded that the binding of $[^3H]$ phenobarbital is a rather non-specific interaction with the plasma membrane

Alteration in elemental and functional composition of heated peat humic acids

The article analyzes the effect of thermal modification of different-type peat on the alteration of elemental and functional composition of peat humic acids. Based on the data of IR-spectra and readings of electron paramagnetic resonance, structural alterations are identified. It is shown that the impact of peat characteristics on humic acids is preserved after thermal modification. It is revealed that the strongest alteration of humic acid composition and properties caused by peat heating are typical to humic acid samples extracted from the peat with low decomposition degree

Frustration - how it can be measured

A misfit parameter is used to characterize the degree of frustration of ordered and disordered systems. It measures the increase of the ground-state energy due to frustration in comparison with that of a relevant reference state. The misfit parameter is calculated for various spin-glass models. It allows one to compare these models with each other. The extension of this concept to other combinatorial optimization problems with frustration, e.g. p-state Potts glasses, graph-partitioning problems and coloring problems is given.Comment: 10 pages, 1 table, no figures, uses revtex.st

Visual similarity in masking and priming: The critical role of task relevance

Cognitive scientists use rapid image sequences to study both the emergence of conscious perception (visual masking) and the unconscious processes involved in response preparation (masked priming). The present study asked two questions: (1) Does image similarity influence masking and priming in the same way? (2) Are similarity effects in both tasks governed by the extent of feature overlap in the images or only by task-relevant features? Participants in Experiment 1 classified human faces using a single dimension even though the faces varied in three dimensions (emotion, race, sex). Abstract geometric shapes and colors were tested in the same way in Experiment 2. Results showed that similarity reduced the visibility of the target in the masking task and increased response speed in the priming task, pointing to a double-dissociation between the two tasks. Results also showed that only task-relevant (not objective) similarity influenced masking and priming, implying that both tasks are influenced from the beginning by intentions of the participant. These findings are interpreted within the framework of a reentrant theory of visual perception. They imply that intentions can influence object formation prior to the separation of vision for perception and vision for action

Electronic structure of the quasi-one-dimensional organic conductor TTF-TCNQ

We study the electronic structure of the quasi-one-dimensional organic conductor TTF-TCNQ by means of density-functional band theory, Hubbard model calculations, and angle-resolved photoelectron spectroscopy (ARPES). The experimental spectra reveal significant quantitative and qualitative discrepancies to band theory. We demonstrate that the dispersive behavior as well as the temperature-dependence of the spectra can be consistently explained by the finite-energy physics of the one-dimensional Hubbard model at metallic doping. The model description can even be made quantitative, if one accounts for an enhanced hopping integral at the surface, most likely caused by a relaxation of the topmost molecular layer. Within this interpretation the ARPES data provide spectroscopic evidence for the existence of spin-charge separation on an energy scale of the conduction band width. The failure of the one-dimensional Hubbard model for the {\it low-energy} spectral behavior is attributed to interchain coupling and the additional effect of electron-phonon interaction.Comment: 18 pages, 9 figure

Dos and don’ts in response priming research

Response priming is a well-understood but sparsely employed paradigm in cognitive science. The method is powerful and well-suited for exploring early visuomotor processing in a wide range of tasks and research fields. Moreover, response priming can be dissociated from visual awareness, possibly because it is based on the first sweep of feedforward processing of primes and targets. This makes it a theoretically interesting device for separating conscious and unconscious vision. We discuss the major opportunities of the paradigm and give specific recommendations (e.g., tracing the time-course of priming in parametric experiments). Also, we point out typical confounds, design flaws, and data processing artifacts

Top-down contingent feature-specific orienting with and without awareness of the visual input

In the present article, the role of endogenous feature-specific orienting for conscious and unconscious vision is reviewed. We start with an overview of orienting. We proceed with a review of masking research, and the definition of the criteria of experimental protocols that demonstrate endogenous and exogenous orienting, respectively. Against this background of criteria, we assess studies of unconscious orienting and come to the conclusion that so far studies of unconscious orienting demonstrated endogenous feature-specific orienting. The review closes with a discussion of the role of unconscious orienting in action control