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Thiourea-Catalyzed Enantioselective Iso-Pictet-Spengler Reactions
A one-pot condensation of isotryptamines and aldehydes that affords enantiomerically enriched 4-substituted tetrahydro--carbolines is reported. The reaction is induced by a chiral thiourea/benzoic acid dual catalyst system. Purification of the N-Boc-protected products by trituration or crystallization provides the optically pure tetrahydro--carboline derivatives in a scalable and highly practical procedure.Chemistry and Chemical Biolog
Interdependence of magnetism and superconductivity in the borocarbide TmNi2B2C
We have discovered a new antiferromagnetic phase in TmNi2B2C by neutron
diffraction. The ordering vector is Q_A = (0.48,0,0) and the phase appears
above a critical in-plane magnetic field of 0.9 T. The field was applied in
order to test the assumption that the zero-field magnetic structure at Q_F =
(0.094,0.094,0) would change into a c-axis ferromagnet if superconductivity
were destroyed. We present theoretical calculations which show that two effects
are important: A suppression of the ferromagnetic component of the RKKY
exchange interaction in the superconducting phase, and a reduction of the
superconducting condensation energy due to the periodic modulation of the
moments at the wave vector Q_A
Mermin-Ho vortex in ferromagnetic spinor Bose-Einstein condensates
The Mermin-Ho and Anderson-Toulouse coreless non-singular vortices are
demonstrated to be thermodynamically stable in ferromagnetic spinor
Bose-Einstein condensates with the hyperfine state F=1. The phase diagram is
established in a plane of the rotation drive vs the total magnetization by
comparing the energies for other competing non-axis-symmetric or singular
vortices. Their stability is also checked by evaluating collective modes.Comment: 4 pages, 4 figure
Energies and damping rates of elementary excitations in spin-1 Bose-Einstein condensed gases
Finite temperature Green's function technique is used to calculate the
energies and damping rates of elementary excitations of the homogeneous,
dilute, spin-1 Bose gases below the Bose-Einstein condensation temperature both
in the density and spin channels. For this purpose the self-consistent
dynamical Hartree-Fock model is formulated, which takes into account the direct
and exchange processes on equal footing by summing up certain classes of
Feynman diagrams. The model is shown to fulfil the Goldstone theorem and to
exhibit the hybridization of one-particle and collective excitations correctly.
The results are applied to the gases of ^{23}Na and ^{87}Rb atoms.Comment: 26 pages, 21 figures. Added 2 new figures, detailed discussio
Polymerization of lignosulfonates by the laccase-HBT (1-hydroxybenzotriazole) system improves dispersibility
The ability of laccases from Trametes villosa (TvL), Myceliophthora thermophila (MtL), Trametes hirsuta (ThL) and Bacillus subtilis (BsL) to improve the dispersion properties of calcium lignosulfonates 398 in the presence of HBT as a mediator was investigated. Size exclusion chromatography showed an extensive increase in molecular weight of the samples incubated with TvL and ThL by 107% and 572% from 28400 Da after 17 h of incubation, respectively. Interestingly, FTIR spectroscopy, 13C NMR and Py-GC/MS analysis of the treated samples suggested no substantial changes in the aromatic signal of the lignosulfonates, a good indication of the ability of TvL/ThL-HBT systems to limit their effect on functional groups without degrading the lignin backbone. Further, the enzymatic treatments led to a general increase in the dispersion properties, indeed a welcome development for its application in polymer blends.Financial support from the BIORENEW EU-project (NMP2-CT-2006-26456), Austrian Academic Exchange Programme (OEAD) and the Spanish projects BIO2007-28720-E, BIO2008-01533, and AGL2008-00709 is acknowledged
Polymerisation of lignosulfonates by the laccase-HBT (1-hydroxybenzotriazole) system improves dispersibility
Prasetyo, Endry Nugroho et al.--The ability of laccases from Trametes villosa (TvL), Myceliophthora thermophila (MtL), Trametes hirsuta (ThL) and Bacillus subtilis (BsL) to improve the dispersion properties of calcium lignosulfonates 398 in the presence of HBT as a mediator was investigated. Size exclusion chromatography showed an extensive increase in molecular weight of the samples incubated with TvL and ThL by 107% and 572% from 28400 Da after 17 h of incubation, respectively. Interestingly, FTIR spectroscopy, 13C NMR and Py-GC/MS analysis of the treated samples suggested no substantial changes in the aromatic signal of the lignosulfonates, a good indication of the ability of TvL/ThL-HBT systems to limit their effect on functional groups without degrading the lignin backbone. Further, the enzymatic treatments led to a general increase in the dispersion properties, indeed a welcome development for its application in polymer blends.Financial support from the BIORENEW EU-project (NMP2-CT-2006-26456), Austrian Academic Exchange Programme (ĂEAD) and the Spanish projects BIO2007-28720-E, BIO2008-01533, and AGL2008-00709 is acknowledged.Peer reviewe
Vortices in multicomponent Bose-Einstein condensates
We review the topic of quantized vortices in multicomponent Bose-Einstein
condensates of dilute atomic gases, with an emphasis on that in two-component
condensates. First, we review the fundamental structure, stability and dynamics
of a single vortex state in a slowly rotating two-component condensates. To
understand recent experimental results, we use the coupled Gross-Pitaevskii
equations and the generalized nonlinear sigma model. An axisymmetric vortex
state, which was observed by the JILA group, can be regarded as a topologically
trivial skyrmion in the pseudospin representation. The internal, coherent
coupling between the two components breaks the axisymmetry of the vortex state,
resulting in a stable vortex molecule (a meron pair). We also mention
unconventional vortex states and monopole excitations in a spin-1 Bose-Einstein
condensate. Next, we discuss a rich variety of vortex states realized in
rapidly rotating two-component Bose-Einstein condensates. We introduce a phase
diagram with axes of rotation frequency and the intercomponent coupling
strength. This phase diagram reveals unconventional vortex states such as a
square lattice, a double-core lattice, vortex stripes and vortex sheets, all of
which are in an experimentally accessible parameter regime. The coherent
coupling leads to an effective attractive interaction between two components,
providing not only a promising candidate to tune the intercomponent interaction
to study the rich vortex phases but also a new regime to explore vortex states
consisting of vortex molecules characterized by anisotropic vorticity. A recent
experiment by the JILA group vindicated the formation of a square vortex
lattice in this system.Comment: 69 pages, 25 figures, Invited review article for International
Journal of Modern Physics
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