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Towards a Framework of Choices Made During the Lifecycles of Process Models
A variety of process modelling approaches exist. The tools provide visualizations and enable analyses of a process. However, analyses of a process depend fundamentally on the properties of the underlying process model. Choices that modellers make in building process models affect the quality of the created models and have an effect on what the models can be used for and can affect the process that is modelled. This paper reflects over the choices the processes modellers need to make in the course of building processes and proposes a framework to show how the choices are related to each other
Anisotropic magnetic behavior of GdBa_2Cu_3O_{6+y} single crystals
Magnetic properties of high-quality Al-free nonsuperconducting
GdBa_2Cu_3O_{6+y} single crystals grown by flux method have been studied. The
magnetic anisotropy below the N\'eel temperature T_N~2.3K corresponds to the
direction of Gd^{3+} magnetic moments along the tetragonal c-axis. At T < T_N
clear indications of spin-flop transitions for H||c have been observed on
magnetization curves at H_{sf}~10kOe. Magnetic phase diagrams have been
obtained for H||c as well as for H||ab. A pronounced anisotropy in the magnetic
susceptibility (unexpected for Gd-based compounds) has been found above T_N.Comment: 2 pages, 3 figures; LT23 (Aug. 2002; Hiroshima), accepted to Physica
Magnetic properties of Gd_{1-x}Pr_xBa_2Cu_3O_{7-y} single crystals
Magnetic properties were studied for the high quality Al-free orthorhombic
Gd_{1-x}Pr_xBa_2Cu_3O_{7-y} single crystals (0<=x<=1.0) grown by the flux
method. An indication on the interaction between the Pr and Cu(2) magnetic
sublattices was found for Pr123. Different signs of magnetic anisotropy were
established for the Pr and Gd ions at low temperatures. It was also shown that
superconductivity reported by Zou et al. [Phys. Rev. Lett. 80 (1998) 1074] for
Pr123 single crystals grown by TSZF method seems to be connected with partial
substitution of Ba for the Pr-sites.Comment: 2 pages (LaTeX2e), 4 EPS figures, phbauth style file included. LT22
conference paper accepted to Physica
Critical properties of the double exchange ferromagnet Nd0.4Pb0.4MnO3
Results of a study of dc-magnetization M(T, H), performed on a Nd0.6Pb0.4MnO3
single crystal in the temperature range around T_C (Curie temperature) which
embraces the critical region | epsilon | = |T -T_C |/T_C <= 0.05 are reported.
The magnetic data analyzed in the critical region using the Kouvel-Fisher
method give the values for the T_C =156.47 +/- 0.06 K and the critical
exponents, beta = 0.374 +/- 0.006 (from the temperature dependence of
magnetization), and gamma = 1.329 +/- 0.003 (from the temperature dependence of
initial susceptibility). The critical isotherm M(T_C, H) gives delta = 4.547
+/- 0.1. Thus the scaling law gamma+beta=delta beta is fulfilled. The critical
exponents obey the single scaling-equation of state M(H, epsilon) = epsilon^b
f_+/- (H/epsilon^(beta + gamma)) where, f_+ for T > T_C and f_- for T< T_C. The
exponent values are very close to those expected for the universality class of
3D Heisenberg ferromagnets with short-range interactions.Comment: 19 pages, including 6 figure
Exotic magnetic orders for high spin ultracold fermions
We study Hubbard models for ultracold bosonic or fermionic atoms loaded into
an optical lattice. The atoms carry a high spin , and interact on site
via strong repulsive Van der Waals forces. Making convenient rearrangements of
the interaction terms, and exploiting their symmetry properties, we derive low
energy effective models with nearest-neighbor interactions, and their
properties. We apply our method to , and 5/2 fermions on two-dimensional
square lattice at quarter, and 1/6 fillings, respectively, and investigate
mean-field equations for repulsive couplings. We find for fermions that
the plaquette state appearing in the highly symmetric SU(4) case does not
require fine tuning, and is stable in an extended region of the phase diagram.
This phase competes with an SU(2) flux state, that is always suppressed for
repulsive interactions in absence of external magnetic field. The SU(2) flux
state has, however, lower energy than the plaquette phase, and stabilizes in
the presence of weak applied magnetic field. For fermions a similar
SU(2) plaquette phase is found to be the ground state without external magnetic
field.Comment: final version, 6 pages, 4 figures, epl forma
Intermediate valence behavior in CeCo9Si4
The novel ternary compound CeCoSi has been studied by means of
specific heat, magnetisation, and transport measurements. Single crystal X-ray
Rietveld refinements reveal a fully ordered distribution of Ce, Co and Si atoms
with the tetragonal space group I4/mcm isostructural with other RCo9Si4. The
smaller lattice constants of CeCo9Si4 in comparison with the trend established
by other RCo9Si4 is indicative for intermediate valence of cerium. While
RCo9Si4 with R= Pr, .. Tb, and Y show ferromagnetism and LaCo9Si4 is nearly
ferromagnetic, CeCo9Si4 remains paramagnetic even in external fields as large
as 40 T, though its electronic specific heat coefficient (g~190 mJ/molK^2) is
of similar magnitude as that of metamagnetic LaCo9Si4 and weakly ferromagnetic
YCo9Si4.Comment: 2 pages, 3 figures, submitted to SCES 0
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