Short-Range B-site Ordering in Inverse Spinel Ferrite NiFe2O4

The Raman spectra of single crystals of NiFe2O4 were studied in various scattering configurations in close comparison with the corresponding spectra of Ni0.7Zn0.3Fe2O4 and Fe3O4. The number of experimentally observed Raman modes exceeds significantly that expected for a normal spinel structure and the polarization properties of most of the Raman lines provide evidence for a microscopic symmetry lower than that given by the Fd-3m space group. We argue that the experimental results can be explained by considering the short range 1:1 ordering of Ni2+ and Fe3+ at the B-sites of inverse spinel structure, most probably of tetragonal P4_122/P4_322 symmetry.Comment: 10 pages, 5 figures, 6 table

Deterministic and controllable photonic scattering media via direct laser writing

Photonic scattering materials, such as biological tissue and white paper, are made of randomly positioned nanoscale inhomogeneities in refractive index that lead to multiple scattering of light. Typically these materials, both naturally-occurring or man-made, are formed through self assembly of the scattering inhomogeneities, which imposes challenges in tailoring the disorder and hence the optical properties. Here, We report on the nanofabrication of photonic scattering media using direct laser writing with deterministic design. These deterministic scattering media consist of submicron thick polymer nanorods that are randomly oriented within a cubic volume. We study the total transmission of light as a function of the number density of rods and of the sample thickness to extract the scattering and transport mean free paths using radiative transfer theory. Such photonic scattering media with deterministic and controllable properties are model systems for fundamental light scattering in particular with strong anisotropy and offer new applications in solid-state lighting and photovoltaics.Comment: 18 pages, 9 figure

Spin flip lifetimes in superconducting atom chips: BCS versus Eliashberg theory

We investigate theoretically the magnetic spin-flip transitions of neutral atoms trapped near a superconducting slab. Our calculations are based on a quantum-theoretical treatment of electromagnetic radiation near dielectric and metallic bodies. Specific results are given for rubidium atoms near a niobium superconductor. At the low frequencies typical of the atomic transitions, we find that BCS theory greatly overestimates coherence effects, which are much less pronounced when quasiparticle lifetime effects are included through Eliashberg theory. At 4.2 K, the typical atomic spin lifetime is found to be larger than a thousand seconds, even for atom-superconductor distances of one micrometer. This constitutes a large enhancement in comparison with normal metals.Comment: 10 pages, 4 figure

The push-through total femoral prosthesis offers a functional alternative to total femoral replacement:a case series

PURPOSE: Oncologic resections or complications of segmental femoral prostheses can result in severe bone loss of the femur for which a total femoral prosthesis (TFP) is required. This study assesses whether the loss of stability and function caused by the loss of muscle attachments can be improved by using a push-through total femoral endoprosthesis (PTTF), because it saves parts of the femur and its muscle attachments. METHODS: In this retrospective case series, ten patients aged 25-77 (mean 54) who received a PTTF between 2005 and 2014 were included for baseline, complications and survival analysis with a mean follow-up of 5.3 (1.1-9.6) years. Functional outcome was assessed in six patients using the Musculoskeletal Tumor Society (MSTS) score, WHO performance scale, Toronto Extremity Salvage Score (TESS), SF36, EQ-5D, NRS pain score, fatigue score and satisfaction score. RESULTS: The mean MSTS score was 64% (23-93%). Five patients had a WHO performance scale of 1, one patient of 3. Mean TESS was 69% (13-90%). SF36 was most notably limited by physical functioning (mean 48), vitality (68) and general health (67). NRS score was 1.9, 1.8 and 8.3 for pain, fatigue and satisfaction, respectively. There were four failures: two infections (one resulting in amputation and one in a minor revision) and two mechanical failures (which required one revision to a TFP and one minor revision). Patient survival was 100%, limb survival 90%, and prosthesis survival 80%. CONCLUSION: The push-through total femoral endoprosthesis allows preservation of muscle attachments and offers a good alternative to total femoral prostheses

The concept of correlated density and its application

The correlated density appears in many physical systems ranging from dense interacting gases up to Fermi liquids which develop a coherent state at low temperatures, the superconductivity. One consequence of the correlated density is the Bernoulli potential in superconductors which compensates forces from dielectric currents. This Bernoulli potential allows to access material parameters. Though within the surface potential these contributions are largely canceled, the bulk measurements with NMR can access this potential. Recent experiments are explained and new ones suggested. The underlying quantum statistical theory in nonequilibrium is the nonlocal kinetic theory developed earlier.Comment: 14 pages, CMT30 proceeding

Bringing Agriculture into the GATT: Designing Acceptable Agricultural Policies

Agricultural and Food Policy, International Relations/Trade,

Comparison among Various Expressions of Complex Admittance for Quantum System in Contact with Heat Reservoir

Relation among various expressions of the complex admittance for quantum systems in contact with heat reservoir is studied. Exact expressions of the complex admittance are derived in various types of formulations of equations of motion under contact with heat reservoir. Namely, the complex admittance is studied in the relaxation method and the external-field method. In the former method, the admittance is calculated using the Kubo formula for quantum systems in contact with heat reservoir in no external driving fields, while in the latter method the admittance is directly calculated from equations of motion with external driving terms. In each method, two types of equation of motions are considered, i.e., the time-convolution (TC) equation and time-convolutionless (TCL) equation. That is, the full of the four cases are studied. It is turned out that the expression of the complex admittance obtained by using the relaxation method with the TC equation exactly coincides with that obtained by using the external-field method with the TC equation, while other two methods give different forms. It is also explicitly demonstrated that all the expressions of the complex admittance coincide with each other in the lowest Born approximation for the systemreservoir interaction. The formulae necessary for the higher order expansions in powers of the system-reservoir interaction are derived, and also the expressions of the admittance in the n-th order approximation are given. To characterize the TC and TCL methods, we study the expressions of the admittances of two exactly solvable models. Each exact form of admittance is compared with the results of the two methods in the lowest Born approximation. It is found that depending on the model, either of TC and TCL would be the better method.Comment: 34pages, no figur

Electrostatic potential in a superconductor

The electrostatic potential in a superconductor is studied. To this end Bardeen's extension of the Ginzburg-Landau theory to low temperatures is used to derive three Ginzburg-Landau equations - the Maxwell equation for the vector potential, the Schroedinger equation for the wave function and the Poisson equation for the electrostatic potential. The electrostatic and the thermodynamic potential compensate each other to a great extent resulting into an effective potential acting on the superconducting condensate. For the Abrikosov vortex lattice in Niobium, numerical solutions are presented and the different contributions to the electrostatic potential and the related charge distribution are discussed.Comment: 19 pages, 11 figure

Scattering of first and second sound waves by quantum vorticity in superfluid Helium

We study the scattering of first and second sound waves by quantum vorticity in superfluid Helium using two-fluid hydrodynamics. The vorticity of the superfluid component and the sound interact because of the nonlinear character of these equations. Explicit expressions for the scattered pressure and temperature are worked out in a first Born approximation, and care is exercised in delimiting the range of validity of the assumptions needed for this approximation to hold. An incident second sound wave will partly convert into first sound, and an incident first sound wave will partly convert into second sound. General considerations show that most incident first sound converts into second sound, but not the other way around. These considerations are validated using a vortex dipole as an explicitely worked out example.Comment: 24 pages, Latex, to appear in Journal of Low Temperature Physic