Critical state modeling of lower-bound threshold stress for clay subgrade

Railway track foundation with fine-grained subgrade, under loading of cyclic nature, can build up excess pore pressure and results in progressive shear failure at a stress level less than its static undrained strength. It is widely accepted a threshold stress level exists, where loading above such level causes large deformation; otherwise stability of vertical track profile will be assured. This paper described the theoretical model that predicts the threshold stress of clay soil. The threshold stress so determined represents the lower-bound solution for bearing strength capacity of clay subgrade which normally exists in an unsaturated state. Developed from the “original Cam-clay” model and validated by series of undrained cyclic triaxial test data on reconstituted kaolin clay, the proposed theoretical model enables the prediction of threshold stress to be made from the fundamental properties of the soil, based on current state of stress and stress history of the sub-grade soil. The model reserved its ability to further expand into predicting the threshold stress of soil in its un-saturated state

Politics without Democracy: A Study of the New Principal Officials Accountability in Hong Kong

his Article seeks to discuss a range of issues related to the POAS. These issues include: The one country, two systems framework; The background to the introduction of the POAS; The fundamentals of the POAS; The notion of accountability pre- and post-POAS; An evaluation of executive government systems; The issues arising from the implementation of POAS; and, A best practice ministerial model for Hong Kong

Some Observations on the Behavior of Soft Clay Under Undrained Cyclic Loading

This note presents the results of a series of cyclic loading triaxial tests under undrained conditions that examines the effectiveness of consolidation history on reconstituted soft clay. For any particular consolidation history, the experimental results confirm the concept of the critical stress level of repeated deviator stress below which a state of non-failure stress equilibrium exists and above which effective stress failure occurs. However, an interesting finding of this study is that for heavily over-consolidated clay, both the state of stress equilibrium (below the critical stress level) and state of effective stress failure (above the critical stress level) develop at the very first few cycles of loading

The Dynamical Distinction between Elliptical and Lenticular Galaxies in Distant Clusters: Further Evidence for the Recent Origin of S0 Galaxies

We examine resolved spectroscopic data obtained with the Keck II telescope for 44 spheroidal galaxies in the fields of two rich clusters, Cl0024+16 (z=0.40) and MS0451-03 (z=0.54), and contrast this with similar data for 23 galaxies within the redshift interval 0.3<z<0.65 in the GOODS northern field. For each galaxy we examine the case for systemic rotation, derive central stellar velocity dispersions sigma and photometric ellipticities, epsilon. Using morphological classifications obtained via Hubble Space Telescope imaging as the basis, we explore the utility of our kinematic quantities in distinguishing between pressure-supported ellipticals and rotationally-supported lenticulars (S0s). We demonstrate the reliability of using the v/(1-epsilon) vs sigma and v/sigma vs epsilon distributions as discriminators, finding that the two criteria correctly identify 63%+-3% and 80%+-2% of S0s at z~0.5, respectively, along with 76%+8-3% and 79%+-2% of ellipticals. We test these diagnostics using equivalent local data in the Coma cluster, and find that the diagnostics are similarly accurate at z=0. Our measured accuracies are comparable to the accuracy of visual classification of morphologies, but avoid the band-shifting and surface brightness effects that hinder visual classification at high redshifts. As an example application of our kinematic discriminators, we then examine the morphology-density relation for elliptical and S0 galaxies separately at z~0.5. We confirm, from kinematic data alone, the recent growth of rotationally-supported spheroidals. We discuss the feasibility of extending the method to a more comprehensive study of cluster and field galaxies to z~1, in order to verify in detail the recent density-dependent growth of S0 galaxies.Comment: 7 pages, 4 figures, updated with version accepted to Ap

Fermions in 3D Optical Lattices: Cooling Protocol to Obtain Antiferromagnetism

A major challenge in realizing antiferromagnetic (AF) and superfluid phases in optical lattices is the ability to cool fermions. We determine the equation of state for the 3D repulsive Fermi-Hubbard model as a function of the chemical potential, temperature and repulsion using unbiased determinantal quantum Monte Carlo methods, and we then use the local density approximation to model a harmonic trap. We show that increasing repulsion leads to cooling, but only in a trap, due to the redistribution of entropy from the center to the metallic wings. Thus, even when the average entropy per particle is larger than that required for antiferromagnetism in the homogeneous system, the trap enables the formation of an AF Mott phase.Comment: 4 pages; 5 figures; also see supplementary material in 2 pages with 1 figur

Superconductor-Insulator Transition and Fermi-Bose Crossovers

The direct transition from an insulator to a superconductor (SC) in Fermi systems is a problem of long-standing interest, which necessarily goes beyond the standard BCS paradigm of superconductivity as a Fermi surface instability. We introduce here a simple, translationally invariant lattice fermion model that undergoes a SC-insulator transition (SIT) and elucidate its properties using analytical methods and quantum Monte Carlo simulations. We show that there is a fermionic band insulator to bosonic insulator crossover in the insulating phase and a BCS-to-BEC crossover in the SC. The SIT is always found to be from a bosonic insulator to a BEC-like SC, with an energy gap for fermions that remains finite across the SIT. The energy scales that go critical at the SIT are the gap to pair excitations in the insulator and the superfluid stiffness in the SC. In addition to giving insight into important questions about the SIT in solid-state systems, our model should be experimentally realizable using ultracold fermions in optical lattices

Facemask use for community protection from air pollution disasters: An ethical overview and framework to guide agency decision making

Disasters involving severe air pollution episodes create a pressing public health issue. During such emergencies, there may be pressure on agencies to provide solutions to protect affected communities. One possible intervention to reduce exposure during such crises is facemasks. Ethical values need to be considered as part of any decision-making process to assess whether to provide advice on, recommend and/or distribute any public health intervention. In this paper, we use principles from public health ethics to analyse the critical ethical issues that relate to agencies providing advice on, recommending and/or distributing facemasks in air pollution disasters, given a lack of evidence of both the specific risk of some polluting events or the effectiveness of facemasks in community settings. The need for reflection on the ethical issues raised by the possible recommendation/use of facemasks to mitigate potential health issues arising from air pollution disasters is critical as communities progressively seek personal interventions to manage perceived and actual risks. This paper develops an ethical decision-making framework to assist agency deliberations. We argue that clarity around decision-making by agencies, after using this framework, may help increase trust about the intervention and solidarity within and between populations affected by these disasters and the agencies who support public health or provide assistance during disasters

Vaccination and Timing Influence SIV Immune Escape Viral Dynamics In Vivo

CD8+ cytotoxic T lymphocytes (CTL) can be effective at controlling HIV-1 in humans and SIV in macaques, but their utility is partly offset by mutational escape. The kinetics of CTL escape and reversion of escape mutant viruses upon transmission to MHC-mismatched hosts can help us understand CTL-mediated viral control and the fitness cost extracted by immune escape mutation. Traditional methods for following CTL escape and reversion are, however, insensitive to minor viral quasispecies. We developed sensitive quantitative real-time PCR assays to track the viral load of SIV Gag164–172 KP9 wild-type (WT) and escape mutant (EM) variants in pigtail macaques. Rapid outgrowth of EM virus occurs during the first few weeks of infection. However, the rate of escape plateaued soon after, revealing a prolonged persistence of WT viremia not detectable by standard cloning and sequencing methods. The rate of escape of KP9 correlated with levels of vaccine-primed KP9-specific CD8+ T cells present at that time. Similarly, when non-KP9 responder (lacking the restricting Mane-A*10 allele) macaques were infected with SHIVmn229 stock containing a mixture of EM and WT virus, rapid reversion to WT was observed over the first 2 weeks following infection. However, the rate of reversion to WT slowed dramatically over the first month of infection. The serial quantitation of escape mutant viruses evolving during SIV infection shows that rapid dynamics of immune escape and reversion can be observed in early infection, particularly when CD8 T cells are primed by vaccination. However, these early rapid rates of escape and reversion are transient and followed by a significant slowing in these rates later during infection, highlighting that the rate of escape is significantly influenced by the timing of its occurrence