Highly oriented and ordered microstructures in block copolymer films

Block copolymer (BCP) films with long-range lateral ordering and orientation are crucial for many applications. Here, we report a simple, versatile strategy based on a solution casting procedure, to produce millimeter thick film of BCPs with highly oriented nanostructures. Transmission electron microscope (TEM), small angle X-ray scattering (SAXS), and Hansen solubility parameters were used to study the morphology and interactions of the system. A variety of BCP-solvent pairs were investigated. Factors including set-up geometry, BCP characteristics, solvent evaporation, surface tension, and interactions, such as solvent-BCP, solvent-substrate, and BCP-substrate were examined. A mechanism is proposed to describe the observed long-range lateral ordering and orientation in films up to 1 mm in thickness. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1369–1375     

A simple polymer electrolyte membrane system for enrichment of low-level tritium (3H) in environmental water samples

Tritium (³H) is an essential tracer of the Earth's water cycle; yet widespread adoption of tritium in hydrologic studies remains a challenge because of analytical barriers to quantification and detection of ³H by electrolytic pre-concentration. Here, we propose a simple tritium electrolytic enrichment system based on the use of solid polymer electrolyte membranes (PEMs) that can be used to enrich ³H in 250–3000?mL environmental water samples to a 10-mL final volume. The IAEA PEM-³H system reported here can produce high enrichment factors (>70-fold) and, importantly, removes some of the deterrents to conventional ³H enrichments methods, including the use of toxic electrolysis and neutralization chemicals, spike standards, a complex electrolysis apparatus that requires extensive cooling and temperature controls, and improves precision by eliminating the need for tracking recovery gravimetrics. Preliminary results with varying operating conditions show ³H enrichments to 70-fold and higher are feasible, spanning a wide range of tritium activities from 5 to 150 TU with a precision of ～4.5?%. Further work is needed to quantify inter-sample memory and to establish lower ³H detection limits. The IAEA PEM-³H system is open source, with 3-D CAD and design files made freely available for adoption and improvement by others.     

Perturbation theory for the effective interaction in nuclei

Starting from a decomposition of the Hamiltonian H(x) of the nuclear many-body problem in the form H(x) = H₀ + xV, where H₀ is a shell-model Hamiltonian, V the residual interaction, and x a strength parameter, we introduce a general effective interaction W(x) describing the interaction of nucleons within a shell, and the associated effective operators $\text{A}\text{?}\text{(x)}$. We display some properties of these operators. From a particular choice of W(x) we obtain the expressions introduced earlier by several authors. The convergence of the expansions for W(x) and $\text{A}\text{?}\text{(x)}$ in powers of x is investigated. It is shown that W(x) and $\text{A}\text{?}\text{(x)}$ are holomorphic in a domain of the complex x-plane including the point x = 0. With the help of a generalization of the von Neumann-Wigner noncrossing rule, we exhibit the nature of the common singularity of W(x) and $\text{A}\text{?}\text{(x)}$ which is closest to the origin and thus defines the radius r₀ of convergence of the expansions of W and $\text{A}\text{?}$. It is shown that r₀ is unaffected by the cancellation of unlinked diagrams. A criterion of consistency is established, which shows that most of the practical calculations of W lead to results which are inconsistent with the definition of W.     

Wireless retrospective gating: Application to cine cardiac imaging

A new “wireless” method of cardiac imaging is introduced, which, unlike ECG triggering, allows imaging the heart at end-diastole, and greatly reduces smearing artifacts in the phase-encoding direction. It is an improvement over ECG-driven retrospective gating, in that patients with poor ECGs can be imaged. This method extends the applicability of cardiac imaging, and since it requires no physiological monitoring hardware, can be implemented easily on any MR imager. The images produced by this method are superior to those from ECG triggering, especially when viewed in a “cine” loop. The technique described herein is, furthermore, extendable to any area where periodic or quasi-periodic motion is a problem.     

Bifurcation and stability of dynamical structures at a current instability

We investigate bifurcation and stability of nonuniform current states at a voltage-controlled current instability. We consider a model which exhibits bulk negative differential conductivity due to Bragg scattering of hot electrons. The system is described by balance equations for momentum and energy densities of the carriers. These transport fields are coupled to Maxwell's equations. The uniform stationary current state is unstable against long-wavelength dielectric relaxation modes at a critical field. We find that the softening of these modes gives rise to a family of periodic travelling waves and to a solitary solution (dipole domain). We show that the periodic travelling waves are unstable, wheras the dipole domain can be stabilized by coupling the sample to a suitable external circuit, if the static impedance of the sample in the domain state is negative. The model describes therefore a discontinuous nonequilibrium transition to a large amplitude domain state.Work Supported by the Swiss National Science Foundation     

A new nodal expansion for classical plasmas

In calculating the equation of state for plasmas we find that diagrammatic expansions for the free energy become unwieldy at high density. At best, many terms must be retained in order to obtain meaningful results. We present a new expansion technique which can be applied to plasmas in the interiors of Jupiter and white dwarf stars. In such cases the older techniques are unsatisfactory because of the size of the ion coupling parameter. Our work yields expansions for which this parameter is supplanted by ion correlation functions, which can be supplied by external computations. In this paper we assume a two-species plasma of classical particles, thereby focusing on combinatorial techniques. The final result is a new nodal expansion in terms of ion correlation functions and an electron coupling parameter.     

Dupin hypersurfaces with four principal Curvatures,II

If M is an isoparametric hypersurface in a sphere S ⁿ with four distinct principal curvatures, then the principal curvatures κ₁, . . . , κ₄ can be ordered so that their multiplicities satisfy m ₁ = m ₂ and m ₃ = m ₄, and the cross-ratio r of the principal curvatures (the Lie curvature) equals −1. In this paper, we prove that if M is an irreducible connected proper Dupin hypersurface in R ⁿ (or S ⁿ ) with four distinct principal curvatures with multiplicities m ₁ = m ₂ ≥ 1 and m ₃ = m ₄ = 1, and constant Lie curvature r = −1, then M is equivalent by Lie sphere transformation to an isoparametric hypersurface in a sphere. This result remains true if the assumption of irreducibility is replaced by compactness and r is merely assumed to be constant.      

Study of phase coexistence in YVO3 and LaVO3

The coexistence at low temperature in YVO₃ and LaVO₃ of two competing phases with defined orbital and spin orientations is studied by Raman spectroscopy. The temperature evolution of the phonons indicates that phase coexistence, due to strain in YVO₃ and fluctuations in LaVO₃, is not restricted to small R ionic radius in RVO₃ compounds. Also, a typical temperature at 50 K is inferred from the temperature dependence of the intensities in LaVO₃. Copyright © 2015 John Wiley & Sons, Ltd.