158 research outputs found
The formation of 3,6-diphenylpyridazine and 2,5-diphenylpyrrole from alpha-styryl azide
Formation of 3,6-diphenylpyridazine and 2,5- diphenylpyrrole from alpha-styryl azid
Acid catalyzed reactions of alpha and beta styryl azides
Acid degradation of alpha and beta styryl azide
Quantum rotational band model for the Heisenberg molecular magnet Mo72Fe30
We derive the low temperature properties of the molecular magnet Mo72Fe30,
where 30 Fe(3+) paramagnetic ions occupy the sites of an icosidodecahedron and
interact via isotropic nearest-neighbour antiferromagnetic Heisenberg exchange.
The key idea of our model (J.S. & M.L.) is that the low-lying excitations form
a sequence of rotational bands, i.e., for each such band the excitation
energies depend quadratically on the total spin quantum number. For
temperatures below 50 mK we predict that the magnetisation is described by a
staircase with 75 equidistant steps as the magnetic field is increased up to a
critical value and saturated for higher fields. For higher temperatures thermal
broadening effects wash out the staircase and yield a linear ramp below the
critical field, and this has been confirmed by our measurements (R.M.). We
demonstrate that the lowest two rotational bands are separated by an energy gap
of 0.7 meV, and this could be tested by EPR and inelastic neutron scattering
measurements. We also predict the occurrence of resonances at temperatures
below 0.1 K in the proton NMR spin-lattice relaxation rate associated with
level crossings. As rotational bands characterize the spectra of many magnetic
molecules our method opens a new road towards a description of their
low-temperature behaviour which is not otherwise accessible.Comment: 7 pages, 6 figures, accepted for Europhysics Letter
Identification and Environmental Assessments for Different Scenarios of Repurposed Decommissioned Wind Turbine Blades
The rapidly growing wind industry poses a fundamental problem for wind turbine blade (WTB) disposal in many areas of
the world. WTBs are primarily manufactured from composites consisting of a thermoset matrix and reinforcing fibers. Currently,
there are no economically viable recycling technologies available for such large-scale composite products. Thus, other
treatment strategies for disposed WTBs have to be considered. This study explores the repurpose of WTBs as a promising
alternative approach from a processual and technological point of view. For this purpose, the study is guided by the categorization
into four different types of repurposed applications: high-loaded complete structure (T1), low-loaded complete
structure (T2), high-loaded segmented structure (T3), and low-loaded segmented structure (T4). A three-dimensional CAD
model of an Enercon-40/500 (E40) wind turbine blade is derived in a reverse engineering procedure to obtain knowledge
about the actual geometry of the WTB. Based on the design, three ecosystems of product scenarios (S) with different
manufacturing technologies involved are investigated: a climbing tower (S1), a playground (S2) and the combination of a
photovoltaic (PV)-floating pontoon, and a lounger (S3). A screening life cycle assessment (LCA) is conducted to evaluate
the three repurposed scenarios according to environmental aspects. It is shown that the repurpose of E40 WTB composite
material can reduce the environmental impact and leads to significant resource savings in relation to a reference product
of similar quality. A particularly high saving potential is identified for the substitution of emission-intensive materials in
construction applications. Furthermore, it is found that transport processes are the primary contributor to the environmental
impact of repurposed applications
Josephson Effect in Fulde-Ferrell-Larkin-Ovchinnikov Superconductors
Due to the difference in the momenta of the superconducting order parameters,
the Josephson current in a Josephson junction between a
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconductor and a conventional BCS
superconductor is suppressed. We show that the Josephson current may be
recovered by applying a magnetic field in the junction. The field strength and
direction at which the supercurrent recovery occurs depend upon the momentum
and structure of the order parameter in the FFLO state. Thus the Josephson
effect provides an unambiguous way to detect the existence of an FFLO state,
and to measure the momentum of the order parameter.Comment: 4 pages with one embedded eps figur
Supercooling of the disordered vortex lattice in Bi_2Sr_2CaCu_2O_8+d
Time-resolved local induction measurements near to the vortex lattice
order-disorder transition in optimally doped
BiSrCaCuO single crystals shows that the
high-field, disordered phase can be quenched to fields as low as half the
transition field. Over an important range of fields, the electrodynamical
behavior of the vortex system is governed by the co-existence of the two phases
in the sample. We interpret the results in terms of supercooling of the
high-field phase and the possible first order nature of the order-disorder
transition at the ``second peak''.Comment: 4 pages, 3 figures. Submitted to Nature, July 10th, 1999; Rejected
August 8th for lack of broad interest Submitted to Physical Review Letters
September 10th, 199
Coexistence of antiferromagnetism and superconductivity in heavy-fermions systems
We report the novel pressure(P)-temperature(T) phase diagrams of
antiferromagnetism (AF) and superconductivity (SC) in CeRhIn, CeIn and
CeCuSi revealed by the NQR measurement. In the itinerant helical magnet
CeRhIn, we found that the N\'eel temperature is reduced at
1.23 GPa with an emergent pseudogap behavior. The coexistence of AF and SC is
found in a narrow P range of 1.63 - 1.75 GPa, followed by the onset of SC with
line-node gap over a wide P window 2.1 - 5 GPa. In CeIn, the localized
magnetic character is robust against the application of pressure up to
1.9 GPa, beyond which the system evolves into an itinerant regime in which the
resistive superconducting phase emerges. We discuss the relationship between
the phase diagram and the magnetic fluctuations. In CeCuSi, the SC and
AF coexist on a microscopic level once its lattice parameter is expanded. We
remark that the underlying marginal antiferromagnetic state is due to
collective magnetic excitations in the superconducting state in CeCuSi.
An interplay between AF and SC is discussed on the SO(5) scenario that unifies
AF and SC. We suggest that the SC and AF in CeCuSi have a common
mechanism.Comment: 6 pages, 5 figures, proceeding of ISSP200
Color Superconductivity in Compact Stars
After a brief review of the phenomena expected in cold dense quark matter,
color superconductivity and color-flavor locking, we sketch some implications
of recent developments in our understanding of cold dense quark matter for the
physics of compact stars. We give a more detailed summary of our recent work on
crystalline color superconductivity and the consequent realization that (some)
pulsar glitches may originate in quark matter.Comment: 19 pages. 2 figures. To appear in the proceedings of the ECT Workshop
on Neutron Star Interiors, Trento, Italy, June 2000. Shorter versions
contributed to the proceedings of Strong and Electroweak Matter 2000,
Marseille, France, June 2000 and to the proceedings of Strangeness 2000,
Berkeley, CA, July 2000. KR was the speaker at all three meeting
On the Meissner Effect of the Odd-Frequency Superconductivity with Critical Spin Fluctuations: Possibility of Zero Field FFLO pairing
We investigate the influence of critical spin fluctuations on electromagnetic
responses in the odd-frequency superconductivity. It is shown that the Meissner
kernel of the odd-frequency superconductivity is strongly reduced by the
critical spin fluctuation or the massless spin wave mode in the
antiferromagnetic phase. These results imply that the superfluid density is
reduced, and the London penetration depth is lengthened for the odd-frequency
pairing. It is also shown that the zero field Flude-Ferrell-Larkin-Ovchinnikov
pairing is spontaneously realized both for even- and odd-frequency in the case
of sufficiently strong coupling with low lying spin-modes.Comment: 10 pages, 7 figure
Crystalline Color Superconductivity
In any context in which color superconductivity arises in nature, it is
likely to involve pairing between species of quarks with differing chemical
potentials. For suitable values of the differences between chemical potentials,
Cooper pairs with nonzero total momentum are favored, as was first realized by
Larkin, Ovchinnikov, Fulde and Ferrell (LOFF). Condensates of this sort
spontaneously break translational and rotational invariance, leading to gaps
which vary periodically in a crystalline pattern. Unlike the original LOFF
state, these crystalline quark matter condensates include both spin zero and
spin one Cooper pairs. We explore the range of parameters for which crystalline
color superconductivity arises in the QCD phase diagram. If in some shell
within the quark matter core of a neutron star (or within a strange quark star)
the quark number densities are such that crystalline color superconductivity
arises, rotational vortices may be pinned in this shell, making it a locus for
glitch phenomena.Comment: 40 pages, LaTeX with eps figs. v2: New paragraph on Ginzburg-Landau
treatment of LOFF phase in section 5. References added. v3: Small changes
only. Version to appear in Phys. Rev.
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