Basic research in wake vortex alleviation using a variable twist wing

The variable twist wing concept was used to investigate the relative effects of lift and turbulence distribution on the rolled up vortex wake. Several methods of reducing the vortex strength behind an aircraft were identified. These involve the redistribution of lift spanwise on the wing and drag distribution along the wing. Initial attempts to use the variable twist wing velocity data to validate the WAKE computer code have shown a strong correlation, although the vorticity levels were not exactly matched

A study of the enzymatic hydrolysis of fish frames using model systems

A model system was employed to study the operating conditions and primary parameters of enzymic hydrolysis of cod proteins. Pancreatin, papain, and bromelain were used to hydrolyse minced cod fillets under controlled conditions and with the rate of hydrolysis being continually monitored via both the pH-stat and TNBS method. The two methods were compared and evaluated. The rate of protein solubilisation was plotted against the degree of hydrolysis (DH). Dry fish protein hydrolysate (FPH) powders having short, medium and high degrees of hydrolysis (DH of approximately 8%, 11% and 16% respectively) were produced and analysed for their molecular weight distribution, using size exclusion chromatography. Almost complete protein solubilisation (75 g soluble protein per kg hydrolysis solution) could be achieved within an hour, at 40°C, at 1% enzyme/substrate ratio (w/w) with papain and bromelain. The pH-stat was found capable of continuously following the rate of hydrolysis but only at low DH. The TNBS could be accurately used even at high DH to estimate the percentage of the peptide bonds cleaved, but required chemical analysis of withdrawn samples

Computer program to generate attitude error equations for a gimballed platform

Computer program for solving attitude error equations related to gimballed platform is described. Program generates matrix elements of attitude error equations when initial matrices and trigonometric identities have been defined. Program is written for IBM 360 computer

A new experimental method for the accelerated characterization of composite materials

The use of composite materials for a variety of practical structural applications is presented and the need for an accelerated characterization procedure is assessed. A new experimental and analytical method is presented which allows the prediction of long term properties from short term tests. Some preliminary experimental results are presented

The viscoelastic behavior of the principal compliance matrix of a unidirectional graphite/epoxy composite

The time-temperature response of the principal compliances of a unidirectional graphite/epoxy composite was determined. It is shown that two components of the compliance matrix are time and temperature independent and that the compliance matrix is symmetric for the viscoelastic composite. The time-temperature superposition principle is used to determine shift factors which are independent of fiber orientation, for fiber angles that vary from 10 D to 90 D with respect to the load direction

The In-Medium Similarity Renormalization Group: A Novel Ab Initio Method for Nuclei

We present a comprehensive review of the In-Medium Similarity Renormalization Group (IM-SRG), a novel ab inito method for nuclei. The IM-SRG employs a continuous unitary transformation of the many-body Hamiltonian to decouple the ground state from all excitations, thereby solving the many-body problem. Starting from a pedagogical introduction of the underlying concepts, the IM-SRG flow equations are developed for systems with and without explicit spherical symmetry. We study different IM-SRG generators that achieve the desired decoupling, and how they affect the details of the IM-SRG flow. Based on calculations of closed-shell nuclei, we assess possible truncations for closing the system of flow equations in practical applications, as well as choices of the reference state. We discuss the issue of center-of-mass factorization and demonstrate that the IM-SRG ground-state wave function exhibits an approximate decoupling of intrinsic and center-of-mass degrees of freedom, similar to Coupled Cluster (CC) wave functions. To put the IM-SRG in context with other many-body methods, in particular many-body perturbation theory and non-perturbative approaches like CC, a detailed perturbative analysis of the IM-SRG flow equations is carried out. We conclude with a discussion of ongoing developments, including IM-SRG calculations with three-nucleon forces, the multi-reference IM-SRG for open-shell nuclei, first non-perturbative derivations of shell- model interactions, and the consistent evolution of operators in the IM-SRG. We dedicate this review to the memory of Gerry Brown, one of the pioneers of many-body calculations of nuclei.Comment: 92 pages, 33 figures, to appear in Physics Report

Optimization of the derivative expansion in the nonperturbative renormalization group

We study the optimization of nonperturbative renormalization group equations truncated both in fields and derivatives. On the example of the Ising model in three dimensions, we show that the Principle of Minimal Sensitivity can be unambiguously implemented at order $\partial^2$ of the derivative expansion. This approach allows us to select optimized cut-off functions and to improve the accuracy of the critical exponents $\nu$ and $\eta$. The convergence of the field expansion is also analyzed. We show in particular that its optimization does not coincide with optimization of the accuracy of the critical exponents.Comment: 13 pages, 9 PS figures, published versio

The Magnus expansion and the in-medium similarity renormalization group

We present an improved variant of the in-medium similarity renormalization group (IM-SRG) based on the Magnus expansion. In the new formulation, one solves flow equations for the anti-hermitian operator that, upon exponentiation, yields the unitary transformation of the IM-SRG. The resulting flow equations can be solved using a first-order Euler method without any loss of accuracy, resulting in substantial memory savings and modest computational speedups. Since one obtains the unitary transformation directly, the transformation of additional operators beyond the Hamiltonian can be accomplished with little additional cost, in sharp contrast to the standard formulation of the IM-SRG. Ground state calculations of the homogeneous electron gas (HEG) and $^{16}$O nucleus are used as test beds to illustrate the efficacy of the Magnus expansion.Comment: 12 pages, 9 figures; fixed typos and added a referenc