1,019 research outputs found
High-field phase diagram of the Haldane-gap antiferromagnet
We have determined the magnetic phase diagram of the quasi-one-dimensional
1 Heisenberg antiferromagnet by
specific heat measurements to 150 mK in temperature and 32 T in magnetic field.
When field is applied along the spin-chain direction, a new phase appears at
T. For the previously known phases of field-induced order,
accurate determination is made of the power-law exponents of the ordering
temperature near the zero-temperature critical field , owing to the
four-fold improvement of the minimum temperature over the previous work. The
results are compared with the predictions based on the Bose-Einstein
condensation of triplet excitations. Substituting deuterium for hydrogen is
found to slightly reduce the interchain exchange.Comment: 6 pages, 6 figure
Bridging the Gap Between Scope-based and Event-based Negation/Speculation Annotations: A Bridge Not Too Far
Specific heat of the spin-dimer antiferromagnet BaMnO in high magnetic fields
We have measured the specific heat of the coupled spin-dimer antiferromagnet
BaMnO to 50 mK in temperature and to 29 T in the magnetic field.
The experiment extends to the midpoint of the field region (25.9 T 32.3 T) of the magnetization plateau at 1/2 of the saturation
magnetization, and reveals the presence of three ordered phases in the field
region between that of the magnetization plateau and the low-field spin-liquid
region. The exponent of the phase boundary with the thermally disordered region
is smaller than the theoretical value based on the Bose-Einstein condensation
of spin triplets. At zero field and 29 T, the specific-heat data show gapped
behaviors characteristic of spin liquids. The zero-field data indicate that the
gapped triplet excitations form two levels whose energies differ by nearly a
factor of two. At least the lower level is well localized. The data at 29 T
reveal that the low-lying excitations at the magnetization plateau are weakly
delocalized.Comment: 6 pages, 5 figures, revised versio
brat: a Web-based Tool for NLP-Assisted Text Annotation
We introduce the brat rapid annotation tool (BRAT), an intuitive web-based tool for text annotation supported by Natural Language Processing (NLP) technology. BRAT has been developed for rich structured annotation for a variety of NLP tasks and aims to support manual curation efforts and increase annotator productivity using NLP techniques. We discuss several case studies of real-world annotation projects using pre-release versions of BRAT and present an evaluation of annotation assisted by semantic class disambiguation on a multicategory entity mention annotation task, showing a 15 % decrease in total annotation time. BRAT is available under an opensource license from
Tomonaga-Luttinger Liquid in a Quasi-One-Dimensional S=1 Antiferromagnet Observed by the Specific Heat
Specific heat experiments on single crystals of the S=1 quasi-one-dimensional
bond-alternating antiferromagnet Ni(C_9H_24N_4)(NO_2)ClO_4, alias NTENP, have
been performed in magnetic fields applied both parallel and perpendicular to
the spin chains. We have found for the parallel field configuration that the
magnetic specific heat (C_mag) is proportional to temperature (T) above a
critical field H_c, at which the energy gap vanishes, in a temperature region
above that of the long-range ordered state. The ratio C_mag/T increases as the
magnetic field approaches H_c from above. The data are in good quantitative
agreement with the prediction of the c=1 conformal field theory in conjunction
with the velocity of the excitations calculated by a numerical diagonalization,
providing a conclusive evidence for a Tomonaga-Luttinger liquid.Comment: 4 pages, 4 postscript figure
Performance Evaluation of the Analyzer Developed for Detection of Dideuterium in Pure Diprotium Environments
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