Detailed study of the hysteresis loops for annealed amorphous alloy wires having vanishing magnetostriction

The evolution of Barkhausen events during the magnetization process in current and furnace annealed Co-based amorphous wire having vanishing magnetostriction, /spl lambda//sub s/, is reported. Their origin is explained using the core-shell model commonly accepted for this class of wire. It is argued that the application of stresses during the annealing process, in wire having slightly negative and slightly positive /spl lambda//sub s/, changes the internal magnetic domain structure. Anisotropy induced by anelastic creep can be used to avoid the formation of these Barkhausen events. The behavior of the coercivity and susceptibility is also reported

Preparation of Cu-based bulk metallic glasses by suction casting

A series of Cu-Hf-Ti alloys prepared by rapid solidification of the melt and by copper mould casting were studied in the present work. Alloy ingots were prepared by arc-melting mixtures of pure metals in an argon atmosphere. An indication of the cooling rate obtained was determined using an Al-4.5 wt%Cu alloy. Cooling rates varied from 540 K/s for the centre section of a 4 mm die to 885 K/s for the outside wall section of the 2 mm die. The glass-forming ability, structure and thermal stability of Cu-Hf-Ti glassy alloys were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and differential thermal analysis (DTA). Bulk glass formation was observed for the Cu64Hf36, Cu55Hf25Ti20 and Cu56Hf25Ti19 alloys, with critical diameters dc for a fully glassy structure of 1, 4 and 5 mm, respectively. The substitution of Hf by Ti increased the glassforming ability (GFA) and the thermal stability

The water balance of urban impermeable surfaces: catchment and process studies

An examination of research and information needs in urban hydrology suggested the investigation of urban water balances and micro- hydrological processes. This should facilitate more accurate modelling of the rainfall-runoff process from urban impermeable surfaces. Greater London data produced annual water balances for 5 heavily urbanized Thames tributaries and estimates of the annual yield ranging from 12-72%. Mean annual runoff for largely rural basins in South East England in comparison was 15-44% of rainfall. The inadequacy of the data for water balance studies led to the instrumentation of a small urbanized catchment at Redbourn, Hertfordshire. Standard meteorological measures were recorded. New instrumentation was designed to measure runoff from shallow pitched roofs while commercially produced instruments were adapted and installed to monitor runoff from a block of flat asphalt-and-chippings garage roofs, and runoff from asphalt roads and pavements at the highway drain outfall. Runoff from these impermeable surfaces is less than 100% even during winter months when evaporation is low. Percentage runoff is 76% for both the pitched and flat roofs while that from the paved surfaces is only 17%. Despite differences in slope, runoff volumes from the pitched and flat roofs are almost identical suggesting that the flat roof does not afford much greater depression storage and evaporation losses. The flat roof does however attenuate storm runoff producing lower flow rates and longer runoff duration than the pitched roofs. Road runoff is very low because of infiltration. The calculated depression storage is 0.25 mm for both roof types and 1.00 mm for the road surface. An average water balance compiled for the roofs gave evaporation as the residual 19% of rainfall. Using an average roof evaporation rate in the road surface water balance gave infiltration as 36% of rainfall with 17% runoff, 21% evaporation and 26% depression storage. Runoff from metre-square roof samples produced slightly different percentage runoff figures for the same winter period. Average percent runoff from red Redland 49 tiles (set at 30°) was 98%, grey Stonewold tiles (set at 17½°) produced 85% and asphalt roofing felt produced 38% runoff. These results are evaluated in the light of probable errors in measurements

High-energy expansion of Coulomb corrections to the e+e- photoproduction cross section

First correction to the high-energy asymptotics of the total $e^+e^-$ photoproduction cross section in the electric field of a heavy atom is derived with the exact account of this field. The consideration is based on the use of the quasiclassical electron Green function in an external electric field. The next-to-leading correction to the cross section is discussed. The influence of screening on the Coulomb corrections is examined in the leading approximation. It turns out that the high-energy asymptotics of the corresponding correction is independent of the photon energy. In the region where both produced particles are relativistic, the corrections to the high-energy asymptotics of the electron (positron) spectrum are derived. Our results for the total cross section are in good agreement with experimental data for photon energies down to a few $MeV$. In addition, the corrections to the bremsstrahlung spectrum are obtained from the corresponding results for pair production.Comment: 22 pages, 7 figures, RevTeX.Typos are corrected. The numerical results, figures and conclusions remain unchanged as they were obtained using correct formula

Lattice QCD and the Schwarz alternating procedure

A numerical simulation algorithm for lattice QCD is described, in which the short- and long-distance effects of the sea quarks are treated separately. The algorithm can be regarded, to some extent, as an implementation at the quantum level of the classical Schwarz alternating procedure for the solution of elliptic partial differential equations. No numerical tests are reported here, but theoretical arguments suggest that the algorithm should work well also at small quark masses.Comment: Plain TeX source, 20 pages, figures include

Learning design studio: educational practice as design inquiry of learning

Recently we are urged to transform education into an evidence based profession, and promote scientific standards or practice. These calls are not new – they seem to emerge every few years. We do not argue with their goal, but we contend that the suitable frame of reference is the paradigm of design science, rather than the common metaphor of medical research. This paper proposes Design Inquiry of Learning as a projection of educational design science into a professional domain, and offers the Learning Design Studio as a pedagogical manifestation of this approach. The learning design studio is a collaborative, blended, project based framework for training educators in effective and evidence-based use of educational technology. We present its theoretical underpinnings, note its fundamental principles and structures, and review three independent cases where it has been trialed. The results show that this model is effective in developing learners’ theoretical knowledge as well as their practical skills, and allows them to link the two. However, it requires a considerable commitment of both learners and tutors, and may not be applicable in more casual settings

Influence of shear flow on vesicles near a wall: a numerical study

We describe the dynamics of three-dimensional fluid vesicles in steady shear flow in the vicinity of a wall. This is analyzed numerically at low Reynolds numbers using a boundary element method. The area-incompressible vesicle exhibits bending elasticity. Forces due to adhesion or gravity oppose the hydrodynamic lift force driving the vesicle away from a wall. We investigate three cases. First, a neutrally buoyant vesicle is placed in the vicinity of a wall which acts only as a geometrical constraint. We find that the lift velocity is linearly proportional to shear rate and decreases with increasing distance between the vesicle and the wall. Second, with a vesicle filled with a denser fluid, we find a stationary hovering state. We present an estimate of the viscous lift force which seems to agree with recent experiments of Lorz et al. [Europhys. Lett., vol. 51, 468 (2000)]. Third, if the wall exerts an additional adhesive force, we investigate the dynamical unbinding transition which occurs at an adhesion strength linearly proportional to the shear rate.Comment: 17 pages (incl. 10 figures), RevTeX (figures in PostScript

Fission widths of hot nuclei from Langevin dynamics

Fission dynamics of excited nuclei is studied in the framework of Langevin equation. The one body wall-and-window friction is used as the dissipative force in the Langevin equation. In addition to the usual wall formula friction, the chaos weighted wall formula developed earlier to account for nonintegrability of single-particle motion within the nuclear volume is also considered here. The fission rate calculated with the chaos weighted wall formula is found to be faster by about a factor of two than that obtained with the usual wall friction. The systematic dependence of fission width on temperature and spin of the fissioning nucleus is investigated and a simple parametric form of fission width is obtained.Comment: RevTex, 12 pages including 9 Postscript figure

A cosmological concordance model with dynamical vacuum term

We demonstrate that creation of dark-matter particles at a constant rate implies the existence of a cosmological term that decays linearly with the Hubble rate. We discuss the cosmological model that arises in this context and test it against observations of the first acoustic peak in the cosmic microwave background (CMB) anisotropy spectrum, the Hubble diagram for supernovas of type Ia (SNIa), the distance scale of baryonic acoustic oscillations (BAO) and the distribution of large scale structures (LSS). We show that a good concordance is obtained, albeit with a higher value of the present matter abundance than in the \Lambda CDM model. We also comment on general features of the CMB anisotropy spectrum and on the cosmic coincidence problem.Comment: Revised version. Accepted for publication in Physics Letters

Prescission neutron multiplicity and fission probability from Langevin dynamics of nuclear fission

A theoretical model of one-body nuclear friction which was developed earlier, namely the chaos-weighted wall formula, is applied to a dynamical description of compound nuclear decay in the framework of the Langevin equation coupled with statistical evaporation of light particles and photons. We have used both the usual wall formula friction and its chaos-weighted version in the Langevin equation to calculate the fission probability and prescission neutron multiplicity for the compound nuclei $^{178}$W, $^{188}$Pt, $^{200}$Pb, $^{213}$Fr, $^{224}$Th, and $^{251}$Es. We have also obtained the contributions of the presaddle and postsaddle neutrons to the total prescission multiplicity. A detailed analysis of our results leads us to conclude that the chaos-weighted wall formula friction can adequately describe the fission dynamics in the presaddle region. This friction, however, turns out to be too weak to describe the postsaddle dynamics properly. This points to the need for a suitable explanation for the enhanced neutron emission in the postsaddle stage of nuclear fission.Comment: RevTex, 14 pages including 5 Postscript figures, results improved by using a different potential, conclusions remain unchanged, to appear in Phys. Rev.