Magnetic correlations of the quasi-one-dimensional half-integer spin-chain antiferromagnets SrM2M_2V2_2O8_8 (MM = Co, Mn)

Magnetic correlations of two iso-structural quasi-one-dimensional (1D) antiferromagnetic spin-chain compounds Sr$M_2$V$_2$O$_8$ ($M$ = Co, Mn) have been investigated by magnetization and powder neutron diffraction. Two different collinear antiferromagnetic (AFM) structures, characterized by the propagation vectors, $k$ = (0 0 1) and $k$ = (0 0 0), have been found below $\sim$ 5.2 K and $\sim$ 42.2 K for the Co- and Mn-compounds, respectively. For the Mn-compound, AFM chains (along the $c$ axis) order ferromagnetically within the $ab$ plane, whereas, for the Co-compound, AFM chains order ferro-/antiferromagnetically along the $a/b$ direction. The critical exponent study confirms that the Co- and Mn-compounds belong to the Ising and Heisenberg universality classes, respectively. For both compounds, short-range spin-spin correlations are present over a wide temperature range above $T_N$. The reduced ordered moments at base temperature (1.5 K) indicate the presence of quantum fluctuations in both compounds due to the quasi-1D magnetic interactions.Comment: 14 pages, 10 figures, 9 table

Weakly Enforced Boundary Conditions for the NURBS-Based Finite Cell Method

In this paper, we present a variationally consistent formulation for the weak enforcement of essential boundary conditions as an extension to the finite cell method, a fictitious domain method of higher order. The absence of boundary fitted elements in fictitious domain or immersed boundary methods significantly restricts a strong enforcement of essential boundary conditions to models where the boundary of the solution domain coincides with the embedding analysis domain. Penalty methods and Lagrange multiplier methods are adequate means to overcome this limitation but often suffer from various drawbacks with severe consequences for a stable and accurate solution of the governing system of equations. In this contribution, we follow the idea of NITSCHE [29] who developed a stable scheme for the solution of the Laplace problem taking weak boundary conditions into account. An extension to problems from linear elasticity shows an appropriate behavior with regard to numerical stability, accuracy and an adequate convergence behavior. NURBS are chosen as a high-order approximation basis to benefit from their smoothness and flexibility in the process of uniform model refinement

Colloidal crystal growth at externally imposed nucleation clusters

We study the conditions under which and how an imposed cluster of fixed colloidal particles at prescribed positions triggers crystal nucleation from a metastable colloidal fluid. Dynamical density functional theory of freezing and Brownian dynamics simulations are applied to a two-dimensional colloidal system with dipolar interactions. The externally imposed nucleation clusters involve colloidal particles either on a rhombic lattice or along two linear arrays separated by a gap. Crystal growth occurs after the peaks of the nucleation cluster have first relaxed to a cutout of the stable bulk crystal.Comment: 4 pages, accepted for publication in Phys. Rev. Let

Non-genetic inheritance, fertility and assisted reproductive technologies

The concept of non-genetic inheritance is gaining considerable attention in the assisted reproductive technology (ART) community due to the reported differences between children born from ART and those that are conceived naturally. It has been demonstrated that children conceived via ART have differences in fetal growth, birth weight, congenital abnormalities, cardiometabolic parameters, glucose homeostasis as well as changes to body composition compared to children conceived naturally. Although these changes may have a parental contribution and may be influenced by the pathology of infertility there is concern that the technologies themselves may play a role. In support of this, is emerging evidence that aspects of ART technology such as culture media formulation and insemination method can alter offspring phenotype. In addition it is also documented that exposure to environmental factors, such as toxins can impact on offspring gametogenesis such that these perturbations persist through generations. With the increasing use of ART and the development of new technologies it is vital that we understand whether ART can effect non-genetic inheritance so that we can optimise technology and prevent abnormal programming and its impact on all aspects of offspring health including fertility and a possible transmission to subsequent generations.Deirdre Zander-Fox, Nicole O McPherson, Michelle Lan

Trends in source gases

Source gases are defined as those gases that, by their breakdown, introduce into the stratosphere halogen, hydrogen, and nitrogen compounds that are important in stratospheric ozone destruction. Given here is an update of the existing concentration time series for chlorocarbons, nitrous oxide, and methane. Also reviewed is information on halogen containing species and the use of these data for establishing trends. Also reviewed is evidence on trends in trace gases that influence tropospheric chemistry and thus the tropospheric lifetimes of source gases, such as carbon dioxide, carbon monoxide, or nitrogen oxides. Much of the information is given in tabular form

Feature Lines for Illustrating Medical Surface Models: Mathematical Background and Survey

This paper provides a tutorial and survey for a specific kind of illustrative visualization technique: feature lines. We examine different feature line methods. For this, we provide the differential geometry behind these concepts and adapt this mathematical field to the discrete differential geometry. All discrete differential geometry terms are explained for triangulated surface meshes. These utilities serve as basis for the feature line methods. We provide the reader with all knowledge to re-implement every feature line method. Furthermore, we summarize the methods and suggest a guideline for which kind of surface which feature line algorithm is best suited. Our work is motivated by, but not restricted to, medical and biological surface models.Comment: 33 page

Acoustic absorption behaviour of a tall carbon nanotube forest

Previous investigations have shown that a 3-mm-high carbon nanotube (CNT) forest has an acoustic absorption coefficient of about 5-10% within the frequency range 125 Hz-4 kHz, which is above that of conventional acoustic materials on a per-mass basis. It was hypothesised that a CNT array of greater height, lower density, and with a non-uniform arrangement of the nanotubes could enhance the amount of acoustic absorption. In order to investigate this hypothesis, an impedance tube test was conducted to measure the acoustic absorption coefficient of a relatively tall 6-mm CNT forest. The results indicate that a greater length and lower density of CNTs may improve the absorption performance of CNT-based acoustic absorbers. Analyses of the results showed anomalies in the measured acoustic absorption coefficient compared with previous investigations. Theoretical analyses were performed based on classical models of acoustic absorption to explain the anomalies. This study describes the factors that may affect the acoustic absorption behaviour of nanomaterials.M. Ayub, A. C. Zander, C. Q. Howard, B. S. Cazzolato, D. M. Huang, N. T. Alvarez, and V. N. Shano

Statistical estimation of trailing edge noise from finite wall-mounted airfoils

The 2016 Joint Conference of The Australian Acoustical Society and The Acoustical Society of New Zealand. Acoustics2016 - The Second Australasian Acoustical Societies ConferenceIt is important to be able to accurately model the flow and noise generated by finite wall-mounted airfoil flows because of the many engineering applications in which these flows occur. One method for predicting turbulent trailing edge noise is the Reynolds-averaged Navier-Stokes based statistical noise model (RSNM) of Doolan et al. (Proceedings of 20th International Congress on Acoustics, ICA 2010). The RSNM method has previously been used successfully on a range of two-dimensional geometry-flow cases. In this paper a new turbulent velocity cross-spectrum model and improved implementation are proposed to allow the RSNM method to be used to effectively and efficiently predict turbulent trailing edge noise from more complex three-dimensional cases. Reynolds-averaged Navier-Stokes (RANS) simulations of a series of wing-in-junction cases are used in combination with the developed acoustic model to predict the far-field noise and compared against experimental noise measurements.Jesse Coombs, Con Doolan, Anthony Zander, Danielle Moreau and Laura Brook

Design of test flows to investigate binary scaling in high enthalpy CO2-N2 mixtures

Binary scaling is a similitude law that facilitates the study of hypersonic flows around blunt bodies. It conserves the Reynolds number and the binary (two-body) reaction rates, which are mainly present in the nonequilibrium layer, and scales properly the convective heat transfer. It requires duplication of the product of density and a length scale of the flow, σL, as well as the free-stream enthalpy, H . Its use for ground-to-flight extrapolation depends on the fractional extent of regions of the flow where higher order reactions become important. This paper presents the design of flow conditions relevant to the study of binary scaling for the X2 super-orbital expansion tube. Flows conditions with similar free-stream enthalpy but distinct free-stream densities were obtained. With the help of numerical simulation, it was confirmed that those conditions were suitable to isolate the effect of binary scaling from the uncertainties and scattering of free-stream conditions