Intermetallic compounds containing $f$-electron elements display a wealth of superconducting phases, which are prime candidates for unconventional pairing with complex order parameter symmetries. For instance, superconductivity has been found at the border of magnetic order as well as deep within ferromagnetically and antiferromagnetically ordered states, suggesting that magnetism may promote rather than destroy superconductivity. Superconducting phases near valence transitions or in the vicinity of magnetopolar order are candidates for new superconductive pairing interactions such as fluctuations of the conduction electron density or the crystal electric field, respectively. The experimental status of the study of the superconducting phases of $f$-electron compounds is reviewed.

Superconducting phases of f -electron compounds

List of contributors Preface Introduction 1 Crystal field splitting mechanisms D J Newman and Betty Ng 2 Empirical crystal fields D J Newman and Betty Ng 3 Fitting crystal field parameters D J Newman and Betty Ng 4 Lanthanide and actinide optical spectra G K Liu 5 Superposition model D J Newman and Betty Ng 6 Effects of electron correlation on crystal field splitting M F Reid and D J Newman 7 Ground state splittings in S-state ions D J Newman and Betty Ng 8 Invariants and moments Y Y Yeung 9 Semiclassical model K S Chan 10 Transition intensities M F Reid Appendix 1 Point symmetry D J Newman and Betty Ng Appendix 2 QBASIC programs D J Newman and Betty Ng Appendix 3 Accessible program packages Y Y Yeung, M F Reid and D J Newman Appendix 4 Computer package CST Cz Rudowicz Bibliography Index

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Crystal Field Handbook

The elastic constants c11, c12 and c44 of U, Np, Pu, and Am telluride single crystals have been obtained by Brillouin scattering from the measured sound velocities in prominent crystallographic directions. In case of the U chalcogenides also by ultrasound techniques. The Cauchy pressure, the Poisson ratio, the anisotropy ratio, the bulk modulus and the Debye temperature have been derived from these data. U and Pu telluride have a negative c12, implying intermediate valence. AmTe has a very low bulk modulus, but a positive c12. It is extremely soft, with a very low sound velocity. For AmTe also the LO and TO phonon frequencies could be determined. The elastic data point to a divalent Am state. The optical reflectivity of the light actinide tellurides (and sometimes of all chalcogenides) has been measured between UV and infrared wavelengths, in the case of AmTe down to the far infrared. The plasma edge of the free carriers has been determined, which yields the ratio of n/m*. Together with the γ value of the specific heat and magnetic data a consistent proposal for the electronic structure of the light actinide chalcogenides can be given. Thus, the Pu chalcogenides are intermediate valent and represent the high-pressure phase of the corresponding Sm chalcogenides. AmTe, as judged by the electronic, optic and magnetic properties seems to be in the 5f7 configuration, i.e. divalent Am, but with a narrow, half-filled (24 meV) wide 5f band, about 0.1 eV below the bottom of the 6d conduction band. We thus propose a new kind of unhybridized heavy fermion. Also AmTe seems to represent a high-pressure phase of EuTe.

Electronic and elastic properties of the light actinide tellurides

With increasing size of wind turbines, new approaches to load control are required to reduce the stresses in blades. Experimental and numerical studies in the fields of helicopter and wind turbine blade research have shown the potential of shape morphing in reducing blade loads. However, because of the large size of modern wind turbine blades, more similarities can be found with wing morphing research than with helicopter blades. Morphing technologies are currently receiving significant interest from the wind turbine community because of their potential high aerodynamic efficiency, simple construction and low weight. However, for actuator forces to be kept low, a compliant structure is needed. This is in apparent contradiction to the requirement for the blade to be load carrying and stiff. This highlights the key challenge for morphing structures in replacing the stiff and strong design of current blades with more compliant structures. Although not comprehensive, this review gives a concise list of the most relevant concepts for morphing structures and materials that achieve compliant shape adaptation for wind turbine blades.

Review of morphing concepts and materials for wind turbine blade applications

The Horace suite of programs has been developed to work with large multiple-measurement data sets collected from time-of-flight neutron spectrometers equipped with arrays of position-sensitive detectors. The software allows exploratory studies of the four dimensions of reciprocal space and excitation energy to be undertaken, enabling multi-dimensional subsets to be visualized, algebraically manipulated, and models for the scattering to simulated or fitted to the data. The software is designed to be an extensible framework, thus allowing user-customized operations to be performed on the data. Examples of the use of its features are given for measurements exploring the spin waves of the simple antiferromagnet RbMnF3 and ferromagnetic iron, and the phonons in URu2Si2.

Horace: Software for the analysis of data from single crystal spectroscopy experiments at time-of-flight neutron instruments

Morphing aircraft structures can significantly enhance air vehicle performance. This paper highlights ongoing work to design novel compliant mechanisms that efficiently morph aircraft structures in order to exploit aerodynamic benefits. Computational tools are being developed to design structures that deform into specified shapes given simple actuator inputs. In addition, these synthesis methods seek to optimize the stiffness of the structure to minimize actuator effort and maximize the stiffness with respect to the environment (external loading). These tools have been used to study two different types of morphing systems: (i) variable geometry wings and (ii) high-frequency vortex generators for active flow control. Several case studies are presented which highlight the design approach and computational and experimental results of these morphing aircraft systems.

Design and application of compliant mechanisms for morphing aircraft structures

This paper describes flight test results of a “Mission Adaptive Compliant Wing” (MACWing) variable geometry trailing edge flap in conjunction with a natural laminar flow airfoil. The MAC-Wing technology provides lightweight, low power, variable geometry reshaping of the upper and lower flap surface with no seams or discontinuities. In this particular program, the airfoil-flap system is optimized to maximize the laminar boundary layer extent over a broad lift coefficient range for endurance aircraft applications. The expanded “laminar bucket” capability allows the endurance aircraft to significantly extend their range (15% or more) by continuously optimizing the wing L/D throughout the mission. The wing was tested at full-scale dynamic pressure, full scale Mach, and reduced-scale Reynolds Numbers on Scaled Composites’ White Knight aircraft. Test results confirmed laminar flow regime up to approximately 60% chord for much of the lift range. Analysis and test results suggest significant fuel savings, weight savings and a higher control authority. Preliminary drag results, future aerodynamic applications and vehicle performance projections are discussed.

Flight testing of Mission Adaptive Compliant Wing

Inelastic neutron scattering has been employed to study in detail the full crystalline-electric-field (CEF) energy scheme in the ground-state J multiplet of ${\mathrm{Er}}^{3+}$ in ${\mathrm{ErBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathit{x}}$ as a function of the oxygen content x. We have been able to resolve the seven ground-state transitions for a series of samples covering the superconducting phase as well as the semiconducting one. J-mixing and intermediate-coupling effects as well as geometrical considerations are shown to be necessary to determine unambiguously the nine CEF parameters of the orthorhombic symmetry. The large energy shifts and intensity changes of the observed CEF spectra as a function of the oxygen content x are shown to be related predominantly to a charge-transfer process from the chains to the planes, the actual charge transfer being in excellent agreement with results derived from bond-valence-sum considerations of diffraction data. The CEF parameters are also used to calculate the magnetization and the field-dependent Schottky anomaly of the heat capacity, which yields remarkable agreement with the experimental data. A mean-field calculation allows us to estimate the x dependence of the saturated moment of the ${\mathrm{Er}}^{3+}$ ion in the ordered phase, which perfectly agrees with the results obtained by means of M\"ossbauer measurements, but considerably deviates from diffraction values.

Neutron-spectroscopic studies of the crystal field in ErBa2Cu3Ox (6 <= x <= 7).

Flow control to avoid or delay boundary-layer separation on a wing can dramatically improve the performance of most air vehicles in strategic parts of their individual flight envelopes. Previous aerodynamic experiments and computations have indicated that unsteady excitation at the appropriate frequency can delay boundary-layer separation and wing stall more effectively than steady flow perturbations and that these unsteady perturbations, when generated in an optimum frequency range, maximize the extent of flow separation control for specific flight conditions. Preliminary aerodynamic experiments have been performed on a deflected trailing-edge flap to evaluate turbulent boundary layer separation control with a deployable high-frequency micro-vortex-generator (HiMVG) array. The HiMVG design tested incorporated emerging displacement amplification compliant structures technology that deployed micro-vortex-generator blades 5 mm, through a range of frequencies between 30 and 70 Hz, when driven by an appropriately sized voice‐coil actuator. The mechanical HiMVG system tested produced an oscillatory stream of boundary-layer embedded vortices that proved effective in mitigating flow separation on the upper surface of a deflected flap when a similar array of static vortex generators could not. A second-generation HiMVG design driven by a piezoelectric actuator was also conceptualized. Candidate flow control applications for this second-generation design are discussed.

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Active Flow Control Using High-Frequency Compliant Structures

An inelastic-neutron-scattering investigation of the dynamic magnetic susceptibility of the heavy-fermion compound CeCu 2 Si 2 is presented. We find evidence for only one crystal-field (CF) transition at 30 meV in addition to quasi-elastic-scattering implying a doublet-quartet level scheme in agreement with specific-heat results but in contradiction with two earlier neutron-scattering studies. Using other experimental results, we propose a set of CF parameters (B 2 0 =-1.29±0.06 meV, B 4 0 =(-4.3±0.2)×10 -3 meV, |B 4 4 |=0.45±0.02 meV) which describe satisfactorily all the measured properties that depend on the CF

R. Osborn

Papers

Design and application of compliant mechanisms for morphing aircraft structures

Flight testing of Mission Adaptive Compliant Wing

Neutron-spectroscopic studies of the crystal field in ErBa2Cu3Ox (6 <= x <= 7).

Active Flow Control Using High-Frequency Compliant Structures

Crystal-field excitations in CeCu2Si2.