1,261 research outputs found
2,2,2-Tris(pyrazol-1-yl)ethanol
The title compound TPE, C11H12N6O, was prepared by slow evaporation from diethyl ether. In the crystal, there is a hydrogen bond between the alcohol H atom and an N in the pyrazole ring of a neighboring molÂecule
Late metal-silicate separation on the IAB parent asteroid: Constraints from combined W and Pt isotopes and thermal modelling
The short-lived Hf-W decay system is a powerful chronometer
for constraining the timing of metal-silicate separation and core formation in
planetesimals and planets. Neutron capture effects on W isotopes, however,
significantly hamper the application of this tool. In order to correct for
neutron capture effects, Pt isotopes have emerged as a reliable in-situ neutron
dosimeter. This study applies this method to IAB iron meteorites, in order to
constrain the timing of metal segregation on the IAB parent body. The
W values obtained for the IAB iron meteorites range from -3.61
0.10 to -2.73 0.09. Correlating Pt with
W data yields a pre-neutron capture W of -2.90 0.06. This
corresponds to a metal-silicate separation age of 6.0 0.8 Ma after CAI
for the IAB parent body, and is interpreted to represent a body-wide melting
event. Later, between 10 and 14 Ma after CAI, an impact led to a catastrophic
break-up and subsequent reassembly of the parent body. Thermal models of the
interior evolution that are consistent with these estimates suggest that the
IAB parent body underwent metal-silicate separation as a result of internal
heating by short-lived radionuclides and accreted at around 1.4 0.1 Ma
after CAIs with a radius of greater than 60 km.Comment: 11 pages, 8 figures, 2 tables; open access article under the CC
BY-NC-ND license (see http://creativecommons.org/licenses/by-nc-nd/4.0/
Feedback rectifiable pairs and stabilization of switched linear systems
We address the feedback design problem for switched linear systems. In
particular we aim to design a switched state-feedback such that the resulting
closed-loop switched system is in upper triangular form. To this effect we
formulate and analyse the feedback rectification problem for pairs of matrices.
We present necessary and sufficient conditions for the feedback rectifiability
of pairs for two subsystems and give a constructive procedure to design
stabilizing state-feedback for a class of switched systems. Several examples
illustrate the characteristics of the problem considered and the application of
the proposed constructive procedure
On the existence of a finite-temperature transition in the two-dimensional gauge glass
Results from Monte Carlo simulations of the two-dimensional gauge glass
supporting a zero-temperature transition are presented. A finite-size scaling
analysis of the correlation length shows that the system does not exhibit
spin-glass order at finite temperatures. These results are compared to earlier
claims of a finite-temperature transition.Comment: 4 pages, 2 figure
[Diphenyldi(pyrazol-1-yl)methane]Âdinitratocobalt(II)
In the title compound, [Co(NO3)2(C19H16N4)], the diphenylÂdipyrazolylmethane ligand coordinates to CoII in a bidentate fashion forming a six-membered ring with an approximate boat configuration. The mean planes of the two pyrazolyl rings are separated by an angle of 39.6 (2)°. The coordination at the CoII center is best described as distorted octaÂhedral with two NO3
− anions serving as bidentate ligands for charge balance. The dihedral angle between the mean planes of the two nitrate rings is 85.0 (1)° and that between the mean planes of the two phenyl rings is 73.7 (1)°. The crystal structure is stabilized by weak interÂmolecular C—H⋯O and intraÂmolecular C—H⋯N hydrogen-bond interÂactions
Two spin liquid phases in the spatially anisotropic triangular Heisenberg model
The quantum spin-1/2 antiferromagnetic Heisenberg model on a two dimensional
triangular lattice geometry with spatial anisotropy is relevant to describe
materials like and organic compounds like
{-(ET)Cu(CN)}. The strength of the spatial anisotropy can
increase quantum fluctuations and can destabilize the magnetically ordered
state leading to non conventional spin liquid phases. In order to understand
these intriguing phenomena, quantum Monte Carlo methods are used to study this
model system as a function of the anisotropic strength, represented by the
ratio between the intra-chain nearest neighbor coupling and the
inter-chain one . We have found evidence of two spin liquid regions. The
first one is stable for small values of the coupling J'/J \alt 0.65, and
appears gapless and fractionalized, whereas the second one is a more
conventional spin liquid with a small spin gap and is energetically favored in
the region 0.65\alt J'/J \alt 0.8. We have also shown that in both spin
liquid phases there is no evidence of broken translation symmetry with dimer or
spin-Peirls order or any broken spatial reflection symmetry of the lattice. The
various phases are in good agreement with the experimental findings, thus
supporting the existence of spin liquid phases in two dimensional quantum
spin-1/2 systems.Comment: 35 pages, 24 figures, 3 table
Phase Transition in the Two-Dimensional Gauge Glass
The two-dimensional XY gauge glass, which describes disordered
superconducting grains in strong magnetic fields, is investigated, with regard
to the possibility of a glass transition. We compute the glass susceptibility
and the correlation function of the system via extensive numerical simulations
and perform the finite-size scaling analysis. This gives strong evidence for a
finite-temperature transition, which is expected to be of a novel type.Comment: 5pages, 3 figures, revtex, to appear in Phys. Rev.
Ground-State Phase Diagram of the Two-Dimensional Quantum Heisenberg Mattis Model
The two-dimensional asymmetric Heisenberg Mattis model is
investigated with the exact diagonalization of finite clusters. The N\'eel
order parameter and the spin glass order parameter can be smoothly extrapolated
to the thermodynamic limit in the antiferromagnetic region, as in the pure
Heisenberg antiferromagnet. The critical concentration of the N\'eel phase is
consistent with that of the two-dimensional Ising Mattis model, and the spin
glass order parameter increases monotonously as the ferro-bond concentration
increases. These facts suggest that quantum fluctuation does not play an
essential role in two-dimensional non-frustrated random spin systems.
KEYWORDS: quantum spin system, ground state, randomness, Mattis model, N\'eel
order, spin glass orderComment: 10 pages, LaTeX, 6 compressed/uuencoded postscript figures, J. Phys.
Soc. Jpn. 65 (1996) No. 2 in pres
Organizational learning and emotion: constructing collective meaning in support of strategic themes
Missing in the organizational learning literature is an integrative framework that reflects the emotional as well as the cognitive dynamics involved. Here, we take a step in this direction by focusing in depth over time (five years) on a selected organization which manufactures electronic equipment for the office industry. Drawing on personal construct theory, we define organizational learning as the collective re-construal of meaning in the direction of strategically significant themes. We suggest that emotions arise as members reflect on progress or lack of progress in achieving organizational learning. Our evidence suggests that invalidation – where organizational learning fails to correspond with expectations – gives rise to anxiety and frustration, while validation – where organizational learning is aligned with or exceeds expectations – evokes comfort or excitement. Our work aims to capture the key emotions involved as organizational learning proceeds
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