Dynamical Structure Factors for Dimerized Spin Systems

We discuss the transition strength between the disordered ground state and the basic low-lying triplet excitation for interacting dimer materials by presenting theoretical calculations and series expansions as well as inelastic neutron scattering results for the material KCuCl_3. We describe in detail the features resulting from the presence of two differently oriented dimers per unit cell and show how energies and spectral weights of the resulting two modes are related to each other. We present results from the perturbation expansion in the interdimer interaction strength and thus demonstrate that the wave vector dependence of the simple dimer approximation is modified in higher orders. Explicit results are given in 10th order for dimers coupled in 1D, and in 2nd order for dimers coupled in 3D with application to KCuCl_3 and TlCuCl_3.Comment: 17 pages, 6 figures, part 2 is based on cond-mat/021133

Random Bond Effect in the Quantum Spin System (Tl1−x_{1-x}Kx_{x})CuCl3_3

The effect of exchange bond randomness on the ground state and the field-induced magnetic ordering was investigated through magnetization measurements in the spin-1/2 mixed quantum spin system (Tl$_{1-x}$K$_{x}$)CuCl$_3$ for $x<0.36$. Both parent compounds TlCuCl$_3$ and KCuCl$_3$ are coupled spin dimer systems, which have the singlet ground state with excitation gaps ${\Delta}/k_{\rm B}=7.7$ K and 31 K, respectively. Due to bond randomness, the singlet ground state turns into the magnetic state with finite susceptibility, nevertheless, the excitation gap remains. Field-induced magnetic ordering, which can be described by the Bose condensation of excited triplets, magnons, was observed as in the parent systems. The phase transition temperature is suppressed by the bond randomness. This behavior may be attributed to the localization effect.Comment: 19 pages, 7 figures, 12 eps files, revtex, will appear in PR

Field-Induced Magnetic Ordering in the Quantum Spin System KCuCl3_3

KCuCl$_3$ is a three-dimensional coupled spin-dimer system and has a singlet ground state with an excitation gap ${\Delta}/k_{\rm B}=31$ K. High-field magnetization measurements for KCuCl$_3$ have been performed in static magnetic fields of up to 30 T and in pulsed magnetic fields of up to 60 T. The entire magnetization curve including the saturation region was obtained at $T=1.3$ K. From the analysis of the magnetization curve, it was found that the exchange parameters determined from the dispersion relations of the magnetic excitations should be reduced, which suggests the importance of the renormalization effect in the magnetic excitations. The field-induced magnetic ordering accompanied by the cusplike minimum of the magnetization was observed as in the isomorphous compound TlCuCl$_3$. The phase boundary was almost independent of the field direction, and is represented by the power law. These results are consistent with the magnon Bose-Einstein condensation picture for field-induced magnetic ordering.Comment: 9 pages, 7 figures, 9 eps files, revtex styl

Ehrenfest relations and magnetoelastic effects in field-induced ordered phases

Magnetoelastic properties in field-induced magnetic ordered phases are studied theoretically based on a Ginzburg-Landau theory. A critical field for the field-induced ordered phase is obtained as a function of temperature and pressure, which determine the phase diagram. It is found that magnetic field dependence of elastic constant decreases discontinuously at the critical field, Hc, and that it decreases linearly with field in the ordered phase (H>Hc). We found an Ehrenfest relation between the field dependence of the elastic constant and the pressure dependence of critical field. Our theory provides the theoretical form for magnetoelastic properties in field- and pressure-induced ordered phases.Comment: 7 pages, 3 figure

INDUSTRIAL AREAS. A SURVEY, ANALYSIS AND APPRAISAL OF THE POTENTIAL FOR CONVERSION OF DISUSED INDUSTRIAL AREAS IN TICINO

This research, promoted by the Università della Svizzera italiana, Accademia di architettura di Mendrisio, through i.CUP (Institute for the Contemporary Urban Project) laid the ground for establishing an observatory of industrial buildings that would give special attention to their fall into disuse and – at the same time – explore the scenarios for appraising the scope for converting potentially disused buildings and land. The study of disused industrial buildings in Ticino revealed considerable scope for the reuse of potentially disused industrial buildings. The data on buildings put to industrial use show that the number of industrial premises in Ticino is 3,681 and that they occupy 2,743 land parcels. The surface area covered by these buildings amounts to 2,503,335 square metres, corresponding to 8.7% of the total area of land built on in the canton. Land parcels accommodating at least one building put to a mainly industrial use account for 14,349,282 square metres of land in Ticino, equal about to 6% of the overall building area of Ticino Canton. Of the above land and building stock, 1,120 buildings (casting off 30.4%) covering a total surface area of 804,591 square metres (casting off 32.1%) (corresponding to the built surface of Bellinzona commune) qualify as potentially disused and the land parcels accommodating them number 813 (casting off 29.6%), 7,058,532 sq m (casting off 49.1%), equating to about half the surface area of Bellinzona commune. An approximate estimate of the volume of the buildings surveyed (the average height is 6 metres) yields a value of 5,000,000 cubic metres.industrial areas, disused buildings, diused land

Modelling flexible thrust performance for trajectory prediction applications in ATM

Reduced thrust operations are of widespread use nowadays due to their inherit benefits for engine conservation. Therefore, in order to enable realistic simulation of air traffic management (ATM) scenarios for purposes such as noise and emissions assessment, a model for reduced thrust is required. This paper proposes a methodology for modelling flexible thrust by combining an assumed temperature (AT) polynomial model identified from manufacturer take-off performance data and public thrust models taken from typical ATM performance databases. The advantage of the proposed AT model is that it only depends on the take-off conditions —runway length, airport altitude, temperature, wind, etc. The results derived from this methodology were compared to simulation data obtained from manufacturer’s take-off performance tools and databases. This comparison revealed that the polynomial model provides AT estimations with sufficient accuracy for their use in ATM simulation. The Base of Aircraft Data (BADA) and the Aircraft Noise and Performance (ANP) database were chosen as representative of aircraft performance models commonly used in ATM simulation. It was observed that there is no significant degradation of the overall accuracy of their thrust models when using AT, while there is a correct capture of the corresponding thrust reduction.Peer ReviewedPostprint (published version

Bose-Einstein condensation of magnons in TlCuCl3_3

A quantitative study of the field-induced magnetic ordering in TlCuCl$_3$ in terms of a Bose-Einstein condensation (BEC) of magnons is presented. It is shown that the hitherto proposed simple BEC scenario is in quantitative and qualitative disagreement with experiment. It is further shown that even very small Dzyaloshinsky-Moriya interactions or a staggered $g$ tensor component of a certain type can change the BEC picture qualitatively. Such terms lead to a nonzero condensate density for all temperatures and a gapped quasiparticle spectrum. Including this type of interaction allows us to obtain good agreement with experimental data.Comment: 2 pages, 2 figures, submitted to SCES'0

Early Christian Ethics

G.E.M. Anscombe famously claimed that ‘the Hebrew-Christian ethic’ differs from consequentialist theories in its ability to ground the claim that killing the innocent is intrinsically wrong. According to Anscombe, this is owing to its legal character, rooted in the divine decrees of the Torah. Divine decrees confer a particular moral sense of ‘ought’ by which this and other act-types can be ‘wrong’ regardless of their consequences, she maintained. There is, of course, a potentially devastating counter-example. Within the Torah, Abraham is apparently commanded by God to slaughter and set fire to his innocent son, Isaac. For attempting to do so, he is praised in the Biblical passage and by later Jewish and Christian commentators. This paper examines rabbinic and early Christian analyses of the story and finds that it was not unambiguously held by these interpreters that God absolutely prohibits killing the innocent, until the time of Augustine, whose position on the story evolved over time

Pressure-Induced Magnetic Quantum Phase Transition in Gapped Spin System KCuCl3

Magnetization and neutron elastic scattering measurements under a hydrostatic pressure were performed on KCuCl3, which is a three-dimensionally coupled spin dimer system with a gapped ground state. It was found that an intradimer interaction decreases with increasing pressure, while the sum of interdimer interactions increases. This leads to the shrinkage of spin gap. A quantum phase transition from a gapped state to an antiferromagnetic state occurs at Pc ? 8.2 kbar. For P > P c, magnetic Bragg reflections were observed at reciprocal lattice points equivalent to those for the lowest magnetic excitation at zero pressure. This confirms that the spin gap decreases and closes under applied pressure.Comment: 7 pages, 10 figures, submitted to J. Phys. Soc. Jp

Dispersive magnetic excitations in the S=1 antiferromagnet Ba3_3Mn2_2O8_8

We present powder inelastic neutron scattering measurements of the S=1 dimerized antiferromagnet Ba$_3$Mn$_2$O$_8$. The $T=1.4$ K magnetic spectrum exhibits a spin-gap of $\Delta \approx 1.0$ meV and a dispersive spectrum with a bandwidth of approximately 1.5 meV. Comparison to coupled dimer models describe the dispersion and scattering intensity accurately and determine the exchange constants in Ba$_3$Mn$_2$O$_8$. The wave vector dependent scattering intensity confirms the proposed S=1 dimer bond. Temperature dependent measurements of the magnetic excitations indicate the presence of both singlet-triplet and thermally activated triplet-quintet excitations.Comment: 8 pages, 8 figures, Submitted to Physical Review B, Resubmited versio