Two-subband system in quantizing magnetic field: Probing many-body gap by non-equilibrium phonons

We study the many-body effects in a two-subband quasi-two-dimensional electron system in a quantizing magnetic field at filling factor three. A manifestation of these effects in the phonon absorption spectroscopy is discussed. The electron system is mapped onto a two-level system with the separation between levels determined by the intersubband splitting and the cyclotron energy. The electron-electron interaction enhances the excitation gap, which exists at all values of the interlevel splitting. This results in a single-peak structure of the phonon absorption rate as a function of magnetic field, instead of the double-peak structure for non-interacting electrons.Comment: 9 pages, 3 figure

25th-order high-temperature expansion results for three-dimensional Ising-like systems on the simple cubic lattice

25th-order high-temperature series are computed for a general nearest-neighbor three-dimensional Ising model with arbitrary potential on the simple cubic lattice. In particular, we consider three improved potentials characterized by suppressed leading scaling corrections. Critical exponents are extracted from high-temperature series specialized to improved potentials, obtaining $\gamma=1.2373(2)$, $\nu=0.63012(16)$, $\alpha=0.1096(5)$, $\eta=0.03639(15)$, $\beta=0.32653(10)$, $\delta=4.7893(8)$. Moreover, biased analyses of the 25th-order series of the standard Ising model provide the estimate $\Delta=0.52(3)$ for the exponent associated with the leading scaling corrections. By the same technique, we study the small-magnetization expansion of the Helmholtz free energy. The results are then applied to the construction of parametric representations of the critical equation of state, using a systematic approach based on a global stationarity condition. Accurate estimates of several universal amplitude ratios are also presented.Comment: 40 pages, 15 figure

Solar sail capture trajectories at Mercury

Mercury is an ideal environment for future planetary exploration by solar sail since it has proved difficult to reach with conventional propulsion and hence remains largely unexplored. In addition, its proximity to the Sun provides a solar sail acceleration of order ten times the sail characteristic acceleration at 1 AU. Conventional capture techniques are shown to be unsuitable for solar sails and a new method is presented. It is shown that capture is bound by upper and lower limits on the orbital elements of the approach orbit and that failure to be within limits results in a catastrophic collision with the planet. These limits are presented for a range of capture inclinations and sail characteristic accelerations. It is found that sail hyperbolic excess velocity is a critical parameter during capture at Mercury, with only a narrow allowed band in order to avoid collision with the planet. The new capture methodis demonstrated for a Mercury sample return mission

A review of the contributions of Dr. Alexander F. H. Goetz to imaging spectroscopy

All aspects of the science and engineering of imaging spectrometry have been advanced by the work of Dr. Alexander F.H. Goetz over the past 30 years. Dr. Goetz¿s pioneering efforts were among the first to realize that it was feasible to obtain laboratory like spectra from space that would quantify earth materials based on biogeochemistry. He has made fundamental contributions to developing high spectral resolution field spectrometers and airborne imaging spectrometers, and to the image processing software and atmospheric correction software needed to analyze the data. These parallel developments in core technologies have made imaging spectroscopy available to a wide range of users of varying user expertise and disciplines, thus enabling the current state of rapid advances in the use of this dat

Critical Currents of Ideal Quantum Hall Superfluids

Filling factor $\nu=1$ bilayer electron systems in the quantum Hall regime have an excitonic-condensate superfluid ground state when the layer separation $d$ is less than a critical value $d_c$. On a quantum Hall plateau current injected and removed through one of the two layers drives a dissipationless edge current that carries parallel currents, and a dissipationless bulk supercurrent that carries opposing currents in the two layers. In this paper we discuss the theory of finite supercurrent bilayer states, both in the presence and in the absence of symmetry breaking inter-layer hybridization. Solutions to the microscopic mean-field equations exist at all condensate phase winding rates for zero and sufficiently weak hybridization strengths. We find, however, that collective instabilities occur when the supercurrent exceeds a critical value determined primarily by a competition between direct and exchange inter-layer Coulomb interactions. The critical current is estimated using a local stability criterion and varies as $(d_c-d)^{1/2}$ when $d$ approaches $d_c$ from below. For large inter-layer hybridization, we find that the critical current is limited by a soliton instability of microscopic origin.Comment: 18 RevTeX pgs, 21 eps figure

Groundwater in fractured bedrock environments: managing catchment and subsurface resources – an introduction

Hard rocks, including crystalline igneous, metamorphic and strongly cemented sedimentary and carbonate rocks, cover about 50% of the Earth's land surface (Singhal & Gupta 2010). Globally, the volume of groundwater contained in hard rock aquifers is not well constrained (Comte et al. 2012) but locally they can be important aquifers (MacDonald et al. 2012), albeit with low groundwater storage and poor primary porosity and permeability. Groundwater flow in these hard rocks is commonly observed to be associated with water-bearing discontinuities, such as fractures, joints and faults (Mazurek 2000; Berkowitz 2002; Font-Capo et al. 2012), and in the weathered regolith (Wright 1992; Chilton & Foster 1995; Deyassa et al. 2014). Structural elements such as fault zones also strongly govern the behaviour of these systems (Forster & Evans 1991; López & Smith 1995; Bense et al. 2013). The nature, abundance, orientation and connectivity of these water-bearing features are largely governed by the history and nature of structural deformation of the bedrock, and commonly impose strong anisotropic flow and transport parameters on these bedrock aquifers (Hsieh et al. 1985; Bour & Davy 1997; Mortimer et al. 2011). Weathering processes furthermore lead to an alteration of bedrock composition and associated aquifer properties resulting in enhanced fracture connectivity and an overall vertical stratification/zonation of bulk aquifer properties, ranging from highly altered shallow regolith horizons to more competent sparsely fractured bedrock at depth (Dewandel et al. 2006; Krásný & Sharp 2007; Lachassagne et al. 2011)

Global development of children’s palliative care: the picture in 2017

Background: The growing interest in tracking the global development of palliative care provision is not matched by research on the development of palliative care services specifically for children. Yet it is estimated that worldwide, 21 million children annually could benefit from the provision of palliative care. We report on a global study of children’s palliative care development and offer suggestions for further improvement in design and method. Methods: Primary data on the level of children’s palliative care development in 2017 was collected from in-country experts through a specific question in an online questionnaire that sought to measure the overall level of palliative care provision globally. Countries were assigned to one of six categories on the basis of the responses obtained. Conflicting responses from the same country were resolved with reference to a hierarchy of preferred respondents. Results: Our data allowed the categorisation of 113 countries, accounting for 65% of the global population aged under 20. Number of countries (% of global child population) in each category were as follows: 1) no known activity, 21 (4%); 2) capacity-building, 16 (24%); 3a) isolated provision, 55 (30%); 3b) generalized provision, 5 (1%); 4a) preliminary integration into mainstream provision, 14 (8%); 4b) advanced integration, 7 (2%). Conclusions: Children’s palliative care at the highest level of provision is available in just 21 countries, accounting for fewer than 10% of the global population aged under 20. It is concentrated in high income settings, whilst the majority of the global need for such care is in low- and middle-income countries. Our study is a useful tool for global advocacy relating to children’s palliative care and a stimulus for the creation of improved indicators to measure it at the country level

Extension to order β23\beta^{23} of the high-temperature expansions for the spin-1/2 Ising model on the simple-cubic and the body-centered-cubic lattices

Using a renormalized linked-cluster-expansion method, we have extended to order $\beta^{23}$ the high-temperature series for the susceptibility $\chi$ and the second-moment correlation length $\xi$ of the spin-1/2 Ising models on the sc and the bcc lattices. A study of these expansions yields updated direct estimates of universal parameters, such as exponents and amplitude ratios, which characterize the critical behavior of $\chi$ and $\xi$. Our best estimates for the inverse critical temperatures are $\beta^{sc}_c=0.221654(1)$ and $\beta^{bcc}_c=0.1573725(6)$. For the susceptibility exponent we get $\gamma=1.2375(6)$ and for the correlation length exponent we get $\nu=0.6302(4)$. The ratio of the critical amplitudes of $\chi$ above and below the critical temperature is estimated to be $C_+/C_-=4.762(8)$. The analogous ratio for $\xi$ is estimated to be $f_+/f_-=1.963(8)$. For the correction-to-scaling amplitude ratio we obtain $a^+_{\xi}/a^+_{\chi}=0.87(6)$.Comment: Misprints corrected, 8 pages, latex, no figure

The interaction of a gap with a free boundary in a two dimensional dimer system

Let $\ell$ be a fixed vertical lattice line of the unit triangular lattice in the plane, and let \Cal H be the half plane to the left of $\ell$. We consider lozenge tilings of \Cal H that have a triangular gap of side-length two and in which $\ell$ is a free boundary - i.e., tiles are allowed to protrude out half-way across $\ell$. We prove that the correlation function of this gap near the free boundary has asymptotics $\frac{1}{4\pi r}$, $r\to\infty$, where $r$ is the distance from the gap to the free boundary. This parallels the electrostatic phenomenon by which the field of an electric charge near a conductor can be obtained by the method of images.Comment: 34 pages, AmS-Te

Scaling in DNA unzipping models: denaturated loops and end-segments as branches of a block copolymer network

For a model of DNA denaturation, exponents describing the distributions of denaturated loops and unzipped end-segments are determined by exact enumeration and by Monte Carlo simulations in two and three dimensions. The loop distributions are consistent with first order thermal denaturation in both cases. Results for end-segments show a coexistence of two distinct power laws in the relative distributions, which is not foreseen by a recent approach in which DNA is treated as a homogeneous network of linear polymer segments. This unexpected feature, and the discrepancies with such an approach, are explained in terms of a refined scaling picture in which a precise distinction is made between network branches representing single stranded and effective double stranded segments.Comment: 8 pages, 8 figure