Conservative implicit schemes for the full potential equation applied to transonic flows

Implicit approximate factorization techniques (AF) were investigated for the solution of matrix equations resulting from finite difference approximations to the full potential equation in conservation form. For transonic flows, an artificial viscosity, required to maintain stability in supersonic regions, was introduced by an upwind bias of the density. Two implicit AF procedures are presented and their convergence performance is compared with that of the standard transonic solution procedure, successive line overrelaxation (SLOR). Subcritical and supercritical test cases are considered. The results indicate that the AF schemes are substantially faster than SLOR

A Bose-Einstein Approach to the Random Partitioning of an Integer

Consider N equally-spaced points on a circle of circumference N. Choose at random n points out of $N$ on this circle and append clockwise an arc of integral length k to each such point. The resulting random set is made of a random number of connected components. Questions such as the evaluation of the probability of random covering and parking configurations, number and length of the gaps are addressed. They are the discrete versions of similar problems raised in the continuum. For each value of k, asymptotic results are presented when n,N both go to infinity according to two different regimes. This model may equivalently be viewed as a random partitioning problem of N items into n recipients. A grand-canonical balls in boxes approach is also supplied, giving some insight into the multiplicities of the box filling amounts or spacings. The latter model is a k-nearest neighbor random graph with N vertices and kn edges. We shall also briefly consider the covering problem in the context of a random graph model with N vertices and n (out-degree 1) edges whose endpoints are no more bound to be neighbors

TAIR: A transonic airfoil analysis computer code

The operation of the TAIR (Transonic AIRfoil) computer code, which uses a fast, fully implicit algorithm to solve the conservative full-potential equation for transonic flow fields about arbitrary airfoils, is described on two levels of sophistication: simplified operation and detailed operation. The program organization and theory are elaborated to simplify modification of TAIR for new applications. Examples with input and output are given for a wide range of cases, including incompressible, subcritical compressible, and transonic calculations

Electronic transport coefficients from ab initio simulations and application to dense liquid hydrogen

Using Kubo's linear response theory, we derive expressions for the frequency-dependent electrical conductivity (Kubo-Greenwood formula), thermopower, and thermal conductivity in a strongly correlated electron system. These are evaluated within ab initio molecular dynamics simulations in order to study the thermoelectric transport coefficients in dense liquid hydrogen, especially near the nonmetal-to-metal transition region. We also observe significant deviations from the widely used Wiedemann-Franz law which is strictly valid only for degenerate systems and give an estimate for its valid scope of application towards lower densities

Norwegian National Program for Lifetime Commissioning and Energy Efficient Operation of Buildings

The project “Life-Time Commissioning for Energy Efficient Operation of Buildings” is actually a network of industrial companies, private and public entities, and R&D organizations. The overall objective of the project is to contribute to the implementation of life-long commissioning of building HVAC systems, so that this becomes a standardized way of building, operating and maintaining the HVAC systems in Norway. The project is organized as an industry research program with minimum duration of five years. Project members pay an annual membership fee. The main goal for the project is to develop, verify, document and implement suitable tools for functional control of energy and indoor environment in buildings under continuous operation during the entire operational life of the building. This will improve energy efficiency and ensure a rational use of energy and a sound indoor environment. All achievements concerning energy improvement will also contribute to the decrease of CO2 emissions

Topological states of multiband superconductors with interband pairing

We study the effects of interband pairing in two-band s-wave and d-wave superconductors with D4h symmetry in both time-reversal invariant as well as time-reversal symmetry breaking states. The presence of interband pairing qualitatively changes the nodal structure of the superconductor: nodes can (dis)appear, merge, and leave high-symmetry locations when interband pairing is tuned. Furthermore, in the d-wave case, we find that also the boundary modes change qualitatively when interband pairing increases: flat zero-energy Andreev bound states gap out and transition to helical edge states.Comment: 19 pages, 11 figure

Curvature condensation and bifurcation in an elastic shell

We study the formation and evolution of localized geometrical defects in an indented cylindrical elastic shell using a combination of experiment and numerical simulation. We find that as a symmetric localized indentation on a semi-cylindrical shell increases, there is a transition from a global mode of deformation to a localized one which leads to the condensation of curvature along a symmetric parabolic crease. This process introduces a soft mode in the system, converting a load-bearing structure into a hinged, kinematic mechanism. Further indentation leads to twinning wherein the parabolic crease bifurcates into two creases that move apart on either side of the line of symmetry. A qualitative theory captures the main features of the phenomena and leads to sharper questions about the nucleation of these defects.Comment: 4 pages, 5 figures, submitted to Physical Review Letter

Nanodiamond-treated flax: improving properties of natural fibers

Synthetic fibers are used extensively as reinforcement in composite materials, but many of them face environmental concerns such as high energy consumption during production and complicated decommissioning. Natural fibers have been considered as an attractive solution for making composites more sustainable. However, they are generally not as strong as synthetic fibers. It is therefore of interest to investigate ways to improve the properties of natural fibers without compromising environmental issues. Here, we present a study of the moisture absorption and mechanical properties of flax that has been exposed to hydrogenated nanodiamonds through an ultrasonic dispersion treatment. Nanodiamonds are known to be non-toxic, unlike many other carbon-based nanomaterials. We show that nanodiamond-treated flax fabric has a lower moisture content (~ −18%), lower moisture absorption rate and better abrasion resistance (~ +30%). Single yarns, extracted from the fabric, show higher tensile strength (~ +24%) compared to untreated flax. Furthermore, we present a theoretical model for the nanodiamond fiber interaction, based on the Derjgauin–Landau–Verwey–Overbeek (DLVO) theory of colloid interactions. The simulations indicate that the mechanical properties improve due to an enhancement of the electrolytic force, dispersion force and hydrogen bonding of nanodiamond-treated fibers, which strengthens the cohesion between the fibers. We also apply the model to nanodiamond-treated cotton. The lower zeta potential of cotton increases the electrolytic force. Comparing the results to experimental data of nanodiamond-treated flax and nanodiamond-treated cotton suggests that the fiber’s zeta potential is critical for the improvements of their mechanical properties. Graphical abstract: [Figure not available: see fulltext.