Shockley model description of surface states in topological insulators

We show that the surface states in topological insulators can be understood based on a well-known Shockley model, a one-dimensional tight-binding model with two atoms per elementary cell, connected via alternating tunneling amplitudes. We generalize the one-dimensional model to the three-dimensional case corresponding to the sequence of layers connected via the amplitudes, which depend on the in-plane momentum p = (p_x,p_y). The Hamiltonian of the model is described a (2 x 2) Hamiltonian with the off-diagonal element t(k,p) depending also on the out-of-plane momentum k. We show that the complex function t(k,p) defines the properties of the surface states. The surface states exist for the in-plane momenta p, where the winding number of the function t(k,p) is non-zero as k is changed from 0 to 2pi. The sign of the winding number defines the sublattice on which the surface states are localized. The equation t(k,p)=0 defines a vortex line in the three-dimensional momentum space. The projection of the vortex line on the two-dimensional momentum p space encircles the domain where the surface states exist. We illustrate how our approach works for a well-known TI model on a diamond lattice. We find that different configurations of the vortex lines are responsible for the "weak" and "strong" topological insulator phases. The phase transition occurs when the vortex lines reconnect from spiral to circular form. We discuss the Shockley model description of Bi_2Se_3 and the applicability of the continuous approximation for the description of the topological edge states. We conclude that the tight-binding model gives a better description of the surface states.Comment: 18 pages, 17 figures; version 3: Sections I-IV revised, Section VII added, Refs. [33]-[35] added; Corresponds to the published versio

Behavior and Failure Mechanism of Composite Slabs

The behavior of a composite slab using a 636 deck profIle was investigated experimentally. Twenty-three one-way slab tests and twenty-four pull-out tests were performed. It was found that the behavior and shear bond load of the composite slab were significantly affected by the depth of the embossment shear key. The average shear stress from the pull-out tests was generally lower than that of the one-way slab tests due to a lack of the transverse load effects which influenced the frictional resistance between the concrete slab and the steel deck

Gauss Sums and Quantum Mechanics

By adapting Feynman's sum over paths method to a quantum mechanical system whose phase space is a torus, a new proof of the Landsberg-Schaar identity for quadratic Gauss sums is given. In contrast to existing non-elementary proofs, which use infinite sums and a limiting process or contour integration, only finite sums are involved. The toroidal nature of the classical phase space leads to discrete position and momentum, and hence discrete time. The corresponding `path integrals' are finite sums whose normalisations are derived and which are shown to intertwine cyclicity and discreteness to give a finite version of Kelvin's method of images.Comment: 14 pages, LaTe

RXTE Observations of 1A 1744-361: Correlated Spectral and Timing Behavior

We analyze Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) data of the transient low mass X-ray binary (LMXB) system 1A 1744-361. We explore the X-ray intensity and spectral evolution of the source, perform timing analysis, and find that 1A 1744-361 shows `atoll' behavior during the outbursts. The color-color diagram indicates that this LMXB was observed in a low intensity spectrally hard (low-hard) state and in a high intensity `banana' state. The low-hard state shows a horizontal pattern in the color-color diagram, and the previously reported `dipper QPO' appears only during this state. We also perform energy spectral analyses, and report the first detection of broad iron emission line and iron absorption edge from 1A 1744-361.Comment: 20 pages, 4 tables, 4 figures, accepted for publication in Ap

The Zel'dovich effect and evolution of atomic Rydberg spectra along the Periodic Table

In 1959 Ya. B. Zel'dovich predicted that the bound-state spectrum of the non-relativistic Coulomb problem distorted at small distances by a short-range potential undergoes a peculiar reconstruction whenever this potential alone supports a low-energy scattering resonance. However documented experimental evidence of this effect has been lacking. Previous theoretical studies of this phenomenon were confined to the regime where the range of the short-ranged potential is much smaller than Bohr's radius of the Coulomb field. We go beyond this limitation by restricting ourselves to highly-excited s states. This allows us to demonstrate that along the Periodic Table of elements the Zel'dovich effect manifests itself as systematic periodic variation of the Rydberg spectra with a period proportional to the cubic root of the atomic number. This dependence, which is supported by analysis of experimental and numerical data, has its origin in the binding properties of the ionic core of the atom.Comment: 17 pages, 12 figure

Isolated aortic root dilation in homocystinuria

BACKGROUND: Vascular complications in homocystinuria have been known for many years, but there have been no reports to date on involvement of the ascending aorta. METHODS: We conducted a cross-sectional study of patients with homocystinuria, known to a single metabolic centre, and evaluated in 2016 with a transthoracic echocardiogram. Aortic root dilation was defined as Z-score ≥ 2.0 SD, and graded mild (Z-score 2.0-3.0), moderate (Z-score 3.01-4.0) and severe (Z-score > 4.0). RESULTS: The study population included 34 patients, median age of 44.3 years (IQR 33.3-52.2), 50% males, 69% diagnosed aged <18 years and 29% pyridoxine-responsive. Eight (24%) had a history of hypertension. Seven patients (21%) were found to have a dilation of the aortic root, mild in two cases (6%), moderate in four (12%) and severe in one (3%). None had dilation of the ascending aorta. Significant aortic regurgitation, secondary to moderate aortic root dilation, was documented in two patients. A single patient had significant mitral regurgitation due to prolapse of both valve leaflets, as well as mild aortic root dilation. Comparing patients with a dilation of the aortic root to those without, there were no significant clinical, laboratory or echocardiographic differences, with the only exception being that the diameter of the ascending aorta was larger in the group with a dilated aortic root, albeit within normal limits. CONCLUSIONS: A subset of patients with homocystinuria have isolated dilation of the aortic root similar to that observed in Marfan syndrome

Resolving confusions about jarrah dieback - don’t forget the plants

The name jarrah dieback has been used for two different disorders, leading to considerable confusion. It was coined in the 1940s to describe the sudden death of groups of jarrah (Eucalyptus marginata) trees in south western Western Australia, which occurred on poorly drained sites, following exceptionally heavy rainfall. In the 1960s these sites were shown to be infested by Phytophthora cinnamomi and jarrah deaths were attributed to it, even though it was only isolated from 5 % of sampled trees. Also the definition of jarrah dieback was expanded to include deaths of many other plants on infested sites, from which P. cinnamomi was more readily isolated. Jarrah trees die from severe water deficiency, indicating problems with water conduction through roots. Xylem vessel diameters vary along roots, being narrow at the root collar, while distally they are larger, providing water storage. Jarrah transpires vigorously during summer, accessing water at depth on sites with deep soil, but being more dependent on internally stored water when root systems are shallower. Following waterlogging, sapwood vessels become blocked with tyloses, reducing both conductivity and potential water storage; such trees may have insufficient water reserves for summer survival. In jarrah P. cinnamomi is unlikely to cause water deficiency because sapwood invasion is rapidly contained in healthy roots. Recent investigations into P. cinnamomi invasion and host responses in other plants show that it can potentially cause a vascular wilt in Banksia spp. and chronic, symptomless infections in herbaceous plants. Susceptibility to waterlogging damage, and/or mortality resulting from infection by P. cinnamomi can only be clarified by detailed knowledge of the hosts and their vulnerabilities. This is essential for making diagnoses, devising management strategies, and avoiding the confusions of the past

Transmission Properties of the oscillating delta-function potential

We derive an exact expression for the transmission amplitude of a particle moving through a harmonically driven delta-function potential by using the method of continued-fractions within the framework of Floquet theory. We prove that the transmission through this potential as a function of the incident energy presents at most two real zeros, that its poles occur at energies $n\hbar\omega+\varepsilon^*$ ($0<Re(\varepsilon^*)<\hbar\omega$), and that the poles and zeros in the transmission amplitude come in pairs with the distance between the zeros and the poles (and their residue) decreasing with increasing energy of the incident particle. We also show the existence of non-resonant "bands" in the transmission amplitude as a function of the strength of the potential and the driving frequency.Comment: 21 pages, 12 figures, 1 tabl

Illuminating the ‘Face’ of Justice: A Meta‐Analytic Examination of Leadership and Organizational Justice

A significant body of research has described effective leader behaviours and has connected these behaviours to positive employee outcomes. However, this research has yet to be systematically integrated with organizational justice research to describe how leader behaviours inform justice perceptions. Therefore, we conduct a meta‐analysis (k = 166, N = 46,034) to investigate how three types of leader behaviours (task, relational, and change) inform four dimensions of organizational justice (procedural, distributive, interpersonal, and informational) referenced to the leader and to the organization. Further, we examine the joint impact of leader behaviours and justice perceptions on social exchange quality (i.e., leader–member exchange), task performance, and job satisfaction. Our results suggest that leader behaviours differentially inform leader‐ and organization‐focused justice perceptions, and the joint effect of leader behaviours and justice perceptions offer more nuanced explanations for outcomes.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/147024/1/joms12402_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147024/2/joms12402.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147024/3/joms12402-sup-0001-TableS1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/147024/4/joms12402-sup-0002-TableS2.pd

Next-to-leading order QCD calculations with parton showers II: soft singularities

Programs that calculate observables in quantum chromodynamics at next-to-leading order typically generate events that consist of partons rather than hadrons -- and just a few partons at that. These programs would be much more useful if the few partons were turned into parton showers, which could be given to one of the Monte Carlo event generators to produce hadron showers. In a previous paper, we have seen how to generate parton showers related to the final state collinear singularities of the perturbative calculation for the example of e+ + e- --> 3 jets. This paper discusses the treatment of the soft singularities.Comment: 26 pages with 5 figures. This version is close to the version to be publishe