An expansive clay for centrifuge modelling

This paper explores the development of an expansive soil which can be repeatedly reproduced for use in centrifuge models to investigate soil-structure interaction problems involving expansive soils. The study considered two materials, namely a sand-bentonite mixture and a naturally occurring, highly expansive clay. For the natural material, two approaches were explored to create a scaled down fissured structure for use in centrifuge testing. The swell behaviour of the two candidate materials was first investigated by means of oedometer tests and then by centrifuge modelling. The centrifuge tests consisted of layers of compacted clay slabs separated by free draining layers. The study revealed that while the sand-bentonite mixture possessed the potential to swell significantly, the time required to do so was impractical for centrifuge studies. It was however found that the approach used to create a scaled down fissured structure in the naturally occurring clay facilitated rapid ingress of water which allowed for significant heave to take place in a much shorter time frame. The results obtained from the centrifuge test conducted on the reworked clay were compared with an empirical heave prediction method and it was found that the swell obtained from the fissured clay matched the predicted heave profile within three hours

Continuum Gauge Fields from Lattice Gauge Fields

On the lattice some of the salient features of pure gauge theories and of gauge theories with fermions in complex representations of the gauge group seem to be lost. These features can be recovered by considering part of the theory in the continuum. The prerequisite for that is the construction of continuum gauge fields from lattice gauge fields. Such a construction, which is gauge covariant and complies with geometrical constructions of the topological charge on the lattice, is given in this paper. The procedure is explicitly carried out in the $U(1)$ theory in two dimensions, where it leads to simple results.Comment: 16 pages, HLRZ 92-3

Desperately Seeking Chiral Fermions

Chiral fermions can (presumably) be constructed by introducing two regulators, one for the gauge fields (e.g. a lattice), and another for the fermion functional integrals in a fixed (regulated) gauge field. This talk discusses cutoff effects arising from the regulator of the fermions.Comment: 4 pages, contribution to Lattice '95 Postscript at http://www-theory.fnal.gov/people/ask/TeX/lat95/chiral.p

Giant magnetic-field changes in radio-frequency absorption in La0.67_{0.67}Sr0.33_{0.33}MnO3_3 near the Curie temperature

The DC transport properties of and the radio-frequency (RF) wave absorption (at 2.525 MHz) in a sample of La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ prepared by floating-zone method are measured. The Curie temperature, $T_{c}$, of the sample is about 374 K. Giant temperature and magnetic-field variations in RF absorption are found in the vicinity of $T_{c}$. Relative change of the RF absorption in magnetic field (magnetoabsorption) is about 67% in field 2.1 kOe and about 55% in field 1 kOe. This giant magnetoabsorption effect can be used to develop RF devices controlled by temperature and low magnetic field. A weak temperature dependence of magnetoabsorption for the sample studied in the range from room temperature to about 350 K makes it especially attractive for practical use. The RF study supplemented with transport, magnetoresistive and magnetic measurements enables us to discuss the optimal properties of manganite samples for observation of giant magnetoabsorption in low field.Comment: Submitted to J. Magn. Magn. Mater., 14 pages including 7 figure

Centrifuge modelling of piled foundations in swelling clays

A study aimed towards assessing the variation in shaft capacity of piled foundations in swelling clays is presented. At the clay’s in-situ water content, the results of pull-out tests on short length piles revealed no dependency of shaft capacity on overburden stress. Conversely, after achieving a targeted value of swell, a strong dependency on overburden stress was observed. In upper portions of the profile where swell can occur relatively freely, swell-induced softening results in a reduction in pile shaft capacity. However, at greater depths where swell is largely suppressed, so too are the effects of swell-induced softening. For this reason, shaft capacity at depth was found to remain relatively constant before and after swell. The results of an instrumented pile test revealed an overriding dependency of lateral induced swell pressure on the magnitude of heave which has occurred. Irrespective of the level of overburden stress, lateral pressures against the pile were found to increase at early stages of the swelling process, but then reduce as swell continued and softening began to occur. Such a result highlights the importance of specifying the level of swell at which shaft capacity should be assessed if a conservative design is to be obtained

Mother-to-Infant Bonding in Women with Postpartum Psychosis and Severe Postpartum Depression: A Clinical Cohort Study

Mother-to-infant bonding is important for long-term child development. The aim of this study was to investigate bonding in women admitted to a Mother and Baby Unit with postpartum depression (PD, n = 64) and postpartum psychosis (PP, n = 91). Participants completed the Postpartum Bonding Questionnaire (PBQ), the Edinburgh Postnatal Depression Scale (EPDS) and the Young Mania Rating Scale (YMRS) weekly during admission. At admission, 57.1% of women with PD had impaired bonding, compared to only 17.6% of women with PP (p-value < 0.001). At discharge, only 18.2% of women with PD and 5.9% of women with PP still experienced impaired bonding (p-value = 0.02). There was a strong association between decrease of depressive and manic symptoms and improved bonding over an eight-week admission period. In a small group of women (5.7%) impaired bonding persisted despite being in remission of their psychiatric disorder. The results from our study show that impaired bonding is a more present and evidently severe problem in postpartum depression but not so much in postpartum psychosis. Treatment of depressive symptoms will improve bonding in almost all women, but clinicians should assess if impaired bonding is still present after remission because for a small group special care and treatment focused on bonding might be required

Electric Field Control of Shallow Donor Impurities in Silicon

We present a tight-binding study of donor impurities in Si, demonstrating the adequacy of this approach for this problem by comparison with effective mass theory and experimental results. We consider the response of the system to an applied electric field: donors near a barrier material and in the presence of an uniform electric field may undergo two different ionization regimes according to the distance of the impurity to the Si/barrier interface. We show that for impurities ~ 5 nm below the barrier, adiabatic ionization is possible within switching times of the order of one picosecond, while for impurities ~ 10 nm or more below the barrier, no adiabatic ionization may be carried out by an external uniform electric field. Our results are discussed in connection with proposed Si:P quantum computer architectures.Comment: 18 pages, 6 figures, submitted to PR

The monopole mass in the three-dimensional Georgi-Glashow model

We study the three-dimensional Georgi-Glashow model to demonstrate how magnetic monopoles can be studied fully non-perturbatively in lattice Monte Carlo simulations, without any assumptions about the smoothness of the field configurations. We examine the apparent contradiction between the conjectured analytic connection of the `broken' and `symmetric' phases, and the interpretation of the mass (i.e., the free energy) of the fully quantised 't Hooft-Polyakov monopole as an order parameter to distinguish the phases. We use Monte Carlo simulations to measure the monopole free energy and its first derivative with respect to the scalar mass. On small volumes we compare this to semi-classical predictions for the monopole. On large volumes we show that the free energy is screened to zero, signalling the formation of a confining monopole condensate. This screening does not allow the monopole mass to be interpreted as an order parameter, resolving the paradox.Comment: 12 pages, 7 figures, uses revtex. Minor changes made to the text to match with the published version at http://link.aps.org/abstract/PRD/v65/e12500

Nonlinear Realization of Chiral Symmetry on the Lattice

We formulate lattice theories in which chiral symmetry is realized nonlinearly on the fermion fields. In this framework the fermion mass term does not break chiral symmetry. This property allows us to use the Wilson term to remove the doubler fermions while maintaining exact chiral symmetry on the lattice. Our lattice formulation enables us to address non-perturbative questions in effective field theories of baryons interacting with pions and in models involving constituent quarks interacting with pions and gluons. We show that a system containing a non-zero density of static baryons interacting with pions can be studied on the lattice without encountering complex action problems. In our formulation one can also decide non-perturbatively if the chiral quark model of Georgi and Manohar provides an appropriate low-energy description of QCD. If so, one could understand why the non-relativistic quark model works.Comment: 34 pages, 2 figures, revised version to be published in J. High Energy Phys. (changes in the 1st paragraph, additional descriptions on the nature of the coordinate singularities in Sec.2, references added