Localized spin fluctuations

Scaling arguments and renormalization group techniques are used in the Anderson model Hamiltonian for the nonmagnetic limit of a magnetic impurity. The range of validity of the theory is limited toU/ 1, where the electron-electron collisions can already compete strongly with the electron-hole collisions. A parquet approximation is developed; it gives for the static susceptibility in the symmetric case = ()^–1 exp (+U/). There are some hints that the exchange force might play a crucial role in the formation of localized magnetic moment. These considerations are consistent with the electron-hole symmetry in the symmetric Anderson model.     

Spin hydrodynamic equations with external disturbances and suitable Green's functions for superfluid3He-B. New onsager relations

The spin hydrodynamic equations for superfluid³He-B have been obtained for the case of external, time-dependent fields. On the basis of a microscopic approach, expressions are found for additional terms in equations containing these fields. Considering the linear response of the system to the switching on of external fields, formulas are found for suitable Green's functions (magnetization-magnetization, rotation-rotation, magnetization-rotation, rotation-magnetization). The rotation-rotation Green's function has the 1/q ² singularity characteristic of superfluid systems. Connections between Green's functions lead to relations among kinetic coefficients v, ₁, and ₂. It is also shown that there is a conserved quantityQ ^(B) = div v _s ^(B) that describes sources or magnetic type charges (monopoles) of the superfluid velocity v _s ^(B) . Comparison with the phenomenological approach suggests thatQ ^(B) is proportional to a pseudoscalar giving the projection of the spin density onto the vector describing the axis of rotation.     

The influence of ageing on the stability of β-γ/γ′ derived microstructures in Ni-Al-Cr-(Co) alloys

Multiphase Ni-Al-(Fe)-(Cr)-(Co)-based intermetallics with (B2)- (A1)/(L1₂), - or - microstructures can exhibit significant room-temperature tensile ductility. In the case of Ni-Al-Cr-based alloys, microstructural development is complicated by the precipitation of -Cr, which can supplant the -phase during ageing of three-phase -/ microstructures. An investigation of the stability, during ageing, of cast Ni-Al-Cr-(Co) alloys with microstructures derived from -/ is reported. In the as-cast condition, the materials investigated consisted of a dendritic matrix containing L1₀ type martensite and interdendritic /. Extensive intra- and interdendritic -Cr precipitation was also observed. The stability during ageing of the interdendritic / microstructure is also considered and transformation of the L1₀ martensite is examined.     

The effect of Si,Zr, Al and Mo on the structure and strength of Ti martensite

The structure and strength of martensite in near titanium alloys have been studied in the composition range (wt %) up to 10% Zr, 6%, Al, 1/2% Mo, 2.4% Si. [0001], 1/3 11¯20 dislocations, 1/3 10¯10 stacking faults and approximately {10¯11} twin related martensite plates are found to be common features of the martensite. Martensite midribs consist either of finely transformed material between martensite plates, or regions of low dislocation density within martensite plates.The martensite morphology is related to the alloy composition, changing from massive to plate-like with increasing solute content. The strength of the martensite is controlled largely by solid solution strengthening.     

Magnetic field dependence of the density of states of YBa2Cu3O6.95: Implications for the vortex structure

The total specific heat of YBa₂Cu₃O_6.95 single crystals includes contributions from phonons and spin-1/2 particles, as well as electronic contributions. The electronic specific heat is described by a quadratic term T² in zero field and a linear term [(0)+(H)]T which is increased when a magnetic field H is applied perpendicular to the CuO₂ planes. In agreement with d-wave superconductivity, we find that _n/T_c and (H)_n(H/H_c2)^1/2, where _n is the coefficient of the normal-state linear term. The H^1/2 dependence of the density of states at the Fermi level was predicted by G. Volovik for lines of nodes in the gap: the quasiparticles which contribute to this density of states are close to the nodes in momentum space and are located outside the vortex core.     

Performance Measurement in the Belgian Document Ordering and Delivery System Impala

This paper deals with performance measures and performance indicators in the Impala electronic document ordering and delivery system for research libraries in Belgium and compares these with some international standards as, e.g., the ProLib/PI study commissioned by the European Commission.Performance measures: Costs (clearinghouse principle) Number of ILL requests made to other libraries Number of ILL requests made to other libraries without success Number of ILL requests made to other libraries with success Number of ILL requests received from other libraries Number of ILL requests received from other libraries and not satisfied Number of ILL requests received from other libraries that were satisfied Frequency asked titlesPerformance indicators: Success rate Borrowing-lending ratio per library Response times, split into several segments of the ILL-procedureThe article concludes with some indications for quality measurement in electronic document delivery where Impala will be able to measure the real supply times as perceived by the end user.     

Effect of elastic interaction energy on coarsening of γ′ precipitates in a mechanically alloyed ODS Ni-base superalloy

The coarsening behavior of precipitates with a uniform size distribution and with a bimodal size distribution in a mechanically alloyed ODS Ni-base superalloy were investigated to clarify the effect of elastic interaction energy on the coarsening behavior of precipitates. The coarsening rate decreased with increasing size of precipitates with a uniform size distribution, contrary to the classical LSW theory, and the coarsening behavior of precipitates with a bimodal size distribution exhibited Ostwald ripening in which the larger precipitates grow at the expense of smaller precipitates. The driving force for coarsening of precipitates was analyzed based on the two-particle model, considering the effect of elastic interaction energy in addition to the effect of interfacial energy. The contribution of elastic interaction energy on the total energy was found to increase with increasing size of precipitates, and the decelerated coarsening of precipitates was attributed to the decrease in the driving force for coarsening with increasing size of precipitates.     

Mössbauer studies of α″-Fe16N2 and α′-Fe8N films

Conversion-electron Mössbauer spectra of epitaxial -Fe₁₆N₂ and -Fe₈N films have been studied and their differences are discussed in detail. The Mössbauer spectrum of -Fe₁₆N₂ can be decomposed into three subspectra, which correspond to the 4d, 8h and 4c sites. The Mössbauer spectrum of -Fe₈N can be fitted using four spectra based on a nitrogen-atom-random-distribution model. The average hyperfine field is larger (3%) for -Fe₁₆N₂ than for -Fe₈N, which is approximately consistent with a 4.1% enhancement of the magnetic moments for -Fe₁₆N₂. The iron moments tend to locate in the film plane for -Fe₁₆N₂ and to arrange perpendicularly to the film plane for -Fe₈N.     

Nonlinear Response of a Continuous Wave NMR Spectrometer for Samples with a Large Magnetization

We present a new insight in the response of a CW NMR spectrometer for highly magnetized samples above 100 MHz. The spectrometer is a bridge made of a magic T. The output of the bridge is proportional to the reflection coefficient, , of a resonant circuit, which is built with a coil containing the sample. The sensitivity of the reflection coefficient to the complex susceptibility of the sample, () = () – j(), depends on the quality factor, Q, of the circuit and filling factor, . When the condition Q 1 is not fulfilled, we show indeed that the use of a simple crystal detector, which is only sensitive to || gives rise to a strong nonlinear response of the spectrometer. Measurements of the complex value of by means of phase sensitive detection allow to recover a linear behavior. We discuss and illustrate those issues with a few circuits we designed for our measurements on liquid ³ He with spin polarizations up to 15 %. A method is described to build in a reproducible and predictable way resonant circuits matched to 50 in the frequency range 100 – 400 MHz with a quality factor as high as 1000 at 4 K.     

On the “scientometric decline” of British science. One additional graph in reply to Ben Martin

With respect to the issue of whether the scientometric measurement of the decline of British science is an artifact of the specific database and underlying assumptions in methods, I argue that there are fewer analytical objections against measurement by usingSciSearch Online than against other methods (based on the fixed journal set and fractional counting). The measurement of international co-authorship, i.e. a network indicator, should not be confounded with measurement of performance of a single nation. The time series for the different subsets of UK-publications, which have been proposed, are given. None of the indicators can be shown to exhibit a trend (in contrast to a drift). The hypothesis of a decline has therefore to be rejected.     

Thermal Expansion and Isothermal Compressibility of TlIn1 – xNdxSe2 (0 ≤ x≤ 0.08) Crystals

The thermal expansion coefficient () and isothermal compressibility ( _T ) of TlIn_{1 – x} Nd _x Se₂(0 x 0.08) crystals were measured between 77 and 400 K. In the range 77–160 K, both and _T increase with temperature, the increase in being much steeper. At higher temperatures, and _T change very little. The observed composition dependences of and _T are interpreted in terms of energy-band structure.     

On chaos in bibliometric terminology

On behalf of a case study of articles on bibliometric selection and ranking the variance in terminology of the properties of journals is shown: the same properties are called in various manners, while one and the same terms have different meanings. Similar inconsistencies are found in the terms denoting readers' activities which are studied in bibliometrics for the assessment of the use of periodicals. The author concludes that there are actually only two properties of periodicals that are quantitatively assessed, viz. productivity, and value. Their definitions are suggested for terminology standardization of general properties of journals and of readers' activities.     

Switching and Hysteresis on the I-V Curves of Submicron BSCCO (2212) Bridges

No Heading In thin BSCCO (2212) whisker-based superconducting bridges with width and length 1 m we observe random telegraph noise at discrete values of current. We show that the noise is associated with spontaneous processes of addition and removal of discrete vortex trains and reflects the regular structure of steps on the I–V curves. The average lifetime of the trains falls down with increasing temperature T in a complex way: intervals of steep drop ( an order of magnitude per Kelvin) are separated with a plateau of (T) with 10^–2 s. The 70 GHz irradiation with 100 W power results in the growth of the average switching frequency by 5 orders of magnitude; thus the HTSC bridges could be efficient detectors of microwave radiation. We discuss the peculiar features of (T).PACS Numbers: 74.25.Fy, 74.40.+k, 74.60.Ge, 74.72.Hs     

The constitution of the Ni-Al-Ru system

The constitution of the Ni-Al-Ru system has been investigated in the range 0 to 50 at% Al. Isothermal sections at 1523 and 1273 K have been determined using microstructural observations, electron probe microanalysis and X-ray diffraction. The phases present were: nickel-based solid solution (); (based on Ni₃Al); solid solutions based on NiAl and RuAl, respectively (designated ₁ and ₂), and ruthenium-based solid solution (Ru). The maximum solubility of Ru in was 5 at%. ₁, and ₂ show extensive range of solubilities, namely up to 20at% Ru in ₁ and up to 25 to 35 at% Ni in ₂. Three-phase equilibrium between , ₂ and (Ru) existed at 1523 and 1273 K. Also at 1523 K, three-phase equilibria existed between , and ₁ and ,₁ and ₂, while at 1273 K, the equilibria were between , ₁,₂ and , , ₂ indicating the occurrence of a reaction +₁, +₂ at a temperature between 1523 and 1273 K. Liquidus features have been deduced from data on as-solidified structures. Lattice parameter data and hardnesses are also reported.     

Anisotropic spin diffusion and multiple spin echoes in3He-4He solutions

We propose a ₁-t₁-₂ pulse-NMR experiment to detect the spin-diffusion anisotropy, =D-D, in degenerate spin-polarized³He-⁴He mixtures, where D and dare the transverse and longitudinal spin diffusion coefficients. In such an experiment the nonlinearity of the dynamics produces multiple spin echoes (MSE). At the ³He concentration x₃ 4% the spinrotation parameter vanishes (M 0), so that the nonlinearity of the equations of motion is entirely due to the anisotropy. In this situation, detection of MSE amounts to observation of D. For slight anisotropy, i.e. D/D 0.25, we use a perturbation scheme similiar to that developed by Einzel et al. (in that case, for small M and small demagnetizing field) to calculate the second and third echo heights. For larger anisotropy we numerically calculate the echo heights. We find that for D/D = 0.5 the heights are 2 % of the first echo, and should be detectable. The (₁, ₂) tip-angle dependence of the D echoes is different from that of the M and demagnetization echoes, and furthermore, they occur at right angles to these echoes (in spin space). Thus, even when small spin-rotation and demagnetization effects are present, the ₁-t₁-₂ experiment provides a sensitive means of detecting the anisotropy.     

On deformation twins and twin-related lamellae in TiAl

The crystal orientation relationships and atomic arrangements across deformation twin planes and twin-related lamellar interfaces in 1 1 0 projection directions in TiAl are examined crystallographically. Atomic arrangements across the true-twin plane and the true-twin-related lamellar interface are shown to be identical, while the atomic arrangements across the pseudo-twin plane and the pseudo-twin-related lamellar interface are quite different. Atom locations at the true-twin plane and the true-twin-related lamellar interface do not violate the atomic order in both crystals while those at the pseudo-twin plane or the pseudo-twin-related lamellar interface are shown to violate the atomic order. 1 1 0 zone diffraction pattern simulations show that the true-twins and the true-twin-related lamellae cannot be distinguished using the 1 1 0 zone diffraction patterns. Not every 1 1 0 zone diffraction pattern can be utilized to distinguish between any two different twin relationships. The true-twin and the pseudo-twin can only be distinguished using 1 0 1] zone diffraction patterns, while true-twin-related and pseudo-twin-related lamellae are distinguishable by only using 1 1 0] zone diffraction patterns.     

Microstructures of titanium-aluminides produced by laser surface alloying

The microstructures of Ti-Al layers (from 43–80 at %Al) produced by laser surface alloying of titanium substrate with a powder feed technique have been investigated. The laser processing parameters were; 1.8 kW laser power, 3 mm beam diameter, 7 mm s^–1 traverse speed, and values of powder flow rates of aluminium ranging from 0.07–0.11 g s^–1. The microstructures were dendrites of ₂ and interdendritic regions of ₂+ in the Ti-43 at %Al alloy; dendrites of either ₂ or ₂+ with interdendritic in the Ti-50 at %Al alloy; dendrites of ₂+ with interdendritic in the Ti-55 at %Al alloy; single phase in the Ti-60 at %Al alloy and TiAl₃ dendrites and Al solid solution in the interdendritic regions in the Ti-80 at %Al alloy. The microstructures were fine and comparable to those produced by other methods of rapid solidification processing. The microstructures of the Ti-50 and Ti-55 at %Al alloys were in agreement with the existence of the peritectic reactions:L + andL + , in the Ti-Al system.     

Phase decomposition of liquid-quenched β-type Ti-Cr alloys

Phase decomposition behaviour of liquid-quenched (bcc) type Ti-Cr alloys was investigated by means of transmission electron microscopy and hardness measurements. It was found that decomposition of to ₁ (Ti-rich, bcc) + ₂ (Ti-lean, bcc) takes place in the intermediate composition range of the Ti-Cr system. This experimental result proves the theoretical prediction made by Menon and Aaronson, but the observed ₁ + ₂ two-phase field expands towards higher temperatures than the predicted binodal line. The coherent ₁ + ₂ two-phase state exhibits the so-called 100 modulated structure and it was concluded that the formation of such a structure is a result of spinodal decomposition of the -phase. We obtained time-temperature-transformation (TTT) diagrams of -type Ti-30, 40 and 50 at % Cr alloys. A typical sequence of structural change is coherent ₁ + ₂ incoherent ₁ + ₂ incoherent ₁ + ₂ + grain boundary precipitates stable state of + TiCr₂ or + TiCr₂. Not all the states in the above sequence appear, depending on alloy composition, liquid-quenching rate and ageing temperature.     

Some observations on the deformation characteristics of bulk polycrystalline zirconium hydrides

The deformation behaviour of bulk polycrystalline zirconium hydrides in the composition range ZrH_1.27 to ZrH_1.66 has been investigated by compressive loading at temperatures between room temperature and 500° C. Single-phase -zirconium hydride is brittle below 100° C. Analyses of slip traces on specimens deformed at temperatures between 100 and 250° C have shown that the glide planes are {111} types. The deformation characteristics of and ( + ) alloys at temperatures between 100 and 500° C are consistent with the hydrogen vacancies in the -phase providing significant lattice friction to the movement of dislocations in the zirconium lattice of the hydride structure. The room temperature fracture stress of ( + ) alloys increases with the volume fraction of the -phase and this can be related to the resistance offered by platelets to the propagation of cleavage cracks in the matrix. In a ( + + ) alloy the resistance to crack propagation at room temperature is further increased by the soft -zirconium phase.     

Distribution of α-AlFeSi and β-AlFeSi particles in surface layer of AA6063 alloy billets after heat treatment

We developed the EPMA mapping method of small -AlFeSi(Al_8.3Fe₂Si) and -AlFeSi(Al_8.9Fe₂Si₂) particles in the billets of Al-Mg-Si alloys such as AA6063 alloys. To discriminate between -AlFeSi and -AlFeSi particles we used the relative X-ray intensities of Fe/Si ratio, the I _Fe/I _Si ratio, instead of the Fe/Si mass ratio. To obtain the I _Fe/I _Si ratio, we used a Monte Carlo method. In this study, using this method the mapping of -AlFeSi and -AlFeSi particles in the surface layer of AA6063 billets after the heat treatment (for 2 h at 580°C) was done. Namely, the distribution of -AlFeSi and -AlFeSi particles of zones from the billet surface to a depth of 800 m was measured. Results showed the zone from the surface to a depth of 200 m was occupied mainly by -AlFeSi particles and the zone from a depth of 200 m toward the center was occupied mainly by -AlFeSi particles. From these results, it was found that if we remove zones from the surface to a depth of 200 m, we can remove the majority of the -AlFeSi particles, and thus improve the quality of anodizing performance of Al-Mg-Si alloys extrusions.