Undrained stability of active and passive trapdoors

The recent growth in the number of sinkhole occurrences due to human activities has highlighted the need for better understanding and prediction of the problem. This paper investigates the use of Broms and Bennermark’s original stability number for trapdoor problems in cohesive soil. The shear-strength-reduction method built in a finite-difference method software program (FLAC) is used to obtain the factor of safety (FOS) under different combinations of pressures for collapse and blowout. Unlike previous research on the use of critical pressure ratios, the FOS results are now functions of the original stability number and depth ratio. The obtained numerical results are compared and validated by using rigorous upper- and lower-bound finite-element limit analysis, as well as other existing solutions available in the literature. Surface failure extents are also examined in the paper. The dimensionless ratios employed in this study are useful for preparing design charts with a broad range of trapdoor geometries and soil parameters

Teaching earth pressure theory using physical models: an example in civil engineering

The transition from basic Engineering courses in the first year of Civil Engineering curriculum, into the analysis and design of Civil Engineering structures can be challenging for students. Indeed, most students find it difficult in learning some of the theoretical courses in later years of their engineering studies. In this paper, discussions will be directed to the role of physical models in assisting the teachings of advanced Civil Engineering courses. Examples of physical models will be shown by making use of those developed by the authors in the teaching of Geotechnical Engineering at University of Southern Queensland, Australia

N-cadherin acts in concert with Slit1-Robo2 signaling in regulating aggregation of placode-derived cranial sensory neurons

Vertebrate cranial sensory ganglia have a dual origin from the neural crest and ectodermal placodes. In the largest of these, the trigeminal ganglion, Slit1-Robo2 signaling is essential for proper ganglion assembly. Here, we demonstrate a crucial role for the cell adhesion molecule N-cadherin and its interaction with Slit1-Robo2 during gangliogenesis in vivo. A common feature of chick trigeminal and epibranchial ganglia is the expression of N-cadherin and Robo2 on placodal neurons and Slit1 on neural crest cells. Interestingly, N-cadherin localizes to intercellular adherens junctions between placodal neurons during ganglion assembly. Depletion of N-cadherin causes loss of proper ganglion coalescence, similar to that observed after loss of Robo2, suggesting that the two pathways might intersect. Consistent with this possibility, blocking or augmenting Slit-Robo signaling modulates N-cadherin protein expression on the placodal cell surface concomitant with alteration in placodal adhesion. Lack of an apparent change in total N-cadherin mRNA or protein levels suggests post-translational regulation. Co-expression of N-cadherin with dominant-negative Robo abrogates the Robo2 loss-of-function phenotype of dispersed ganglia, whereas loss of N-cadherin reverses the aberrant aggregation induced by increased Slit-Robo expression. Our study suggests a novel mechanism whereby N-cadherin acts in concert with Slit-Robo signaling in mediating the placodal cell adhesion required for proper gangliogenesis

Composite boson signature in the interference pattern of atomic dimer condensates

We predict the existence of high frequency modes in the interference pattern of two condensates made of fermionic-atom dimers. These modes, which result from fermion exchanges between condensates, constitute a striking signature of the dimer composite nature. From the 2-coboson spatial correlation function, that we derive analytically, and the Shiva diagrams that visualize many-body effects specific to composite bosons, we identify the physical origin of these high frequency modes and determine the conditions to see them experimentally by using bound fermionic-atom pairs trapped on optical lattice sites. The dimer granularity which appears in these modes comes from Pauli blocking that prevents two dimers to be located at the same lattice site.Comment: 10+7 pp, 3 figures. v2: version accepted for publication in New J. Phy

Assessing statistical reasoning in descriptive statistics: a qualitative meta-analysis

To date, there are abundant studies on statistical reasoning in descriptive statistics and inferential statistics. Nevertheless, the types of statistical reasoning assessments used in those studies are different from each other. Hence, this qualitative meta-analysis is aimed to explore the methods utilized in assessing statistical reasoning among students from all levels in descriptive statistics. A total of 36 studies on reasoning about measures of central tendency, variability and distribution were found and reviewed in this paper. It was noticed that six major types of methods were employed to assess students’ statistical reasoning in descriptive statistics, namely interview, survey or questionnaire, tasks, tests, minute paper, and teaching. This study contributes considerably to the statistical reasoning area as it provides new information on statistical reasoning in descriptive statistics. For future studies, some recommendations are proposed to improve statistical reasoning assessments

Way to observe the implausible "trion-polariton"

Using the composite boson (coboson) many-body formalism, we determine under which conditions "trion-polariton" can exist. Dipolar attraction can bind an exciton and an electron into a trion having an energy well separated from the exciton energy. Yet, the existence of long-lived "trion-polariton" is a priori implausible not only because the photon-trion coupling, which scales as the inverse of the sample volume, is vanishingly small, but mostly because this coupling is intrinsically "weak". Here, we show that a moderately dense Fermi sea renders its observation possible: on the pro side, the Fermi sea overcomes the weak coupling by pinning the photon to its momentum through Pauli blocking, it also overcomes the dramatically poor photon-trion coupling by providing a volume-linear trion subspace to which the photon is coherently coupled. On the con side, the Fermi sea broadens the photon-trion resonance due to the fermionic nature of trions and electrons, it also weakens the trion binding by blocking electronic states relevant for trion formation. As a result, the proper way to observe this novel polariton is to use doped semiconductor having long-lived electronic states, highly-bound trion and Fermi energy as large as a fraction of the trion binding energy.Comment: 6 pages, 3 figure

Cross-over from trion-hole to exciton-polaron in n-doped semiconductor quantum wells

We present a theoretical study of photo-absorption in n-doped two-dimensional (2D) and quasi-2D semiconductors that takes into account the interaction of the photocreated exciton with Fermi-sea (FS) electrons through (i) Pauli blocking, (ii) Coulomb screening, and (iii) excitation of FS electron-hole pairs---that we here restrict to one. The system we tackle is thus made of one exciton plus zero or one FS electron-hole pair. At low doping, the system ground state is predominantly made of a "trion-hole"---a trion (two opposite-spin electrons plus a valence hole) weakly bound to a FS hole---with a small exciton component. As the trion is poorly coupled to photon, the intensity of the lowest absorption peak is weak; it increases with doping, thanks to the growing exciton component, due to a larger coupling between 2-particle and 4-particle states. Under a further doping increase, the trion-hole complex is less bound because of Pauli blocking by FS electrons, and its energy increases. The lower peak then becomes predominantly due to an exciton dressed by FS electron-hole pairs, that is, an exciton-polaron. As a result, the absorption spectra of $n$-doped semiconductor quantum wells show two prominent peaks, the nature of the lowest peak turning from trion-hole to exciton-polaron under a doping increase. Our work also nails down the physical mechanism behind the increase with doping of the energy separation between the trion-hole peak and the exciton-polaron peak, even before the anti-crossing, as experimentally observed.Comment: 20 pages, 10 figure