2,072 research outputs found
Logarithmic correction to the Bekenstein-Hawking entropy of the BTZ black hole
We derive an exact expression for the partition function of the Euclidean BTZ
black hole. Using this, we show that for a black hole with large horizon area,
the correction to the Bekenstein-Hawking entropy is , in
agreement with that for the Schwarzschild black hole obtained in the canonical
gravity formalism and also in a Lorentzian computation of BTZ black hole
entropy. We find that the right expression for the logarithmic correction in
the context of the BTZ black hole comes from the modular invariance associated
with the toral boundary of the black hole.Comment: LaTeX, 10 pages, typos corrected, clarifications adde
BTZ Black Hole Entropy from Ponzano-Regge Gravity
The entropy of the BTZ black hole is computed in the Ponzano-Regge
formulation of three-dimensional lattice gravity. It is seen that the correct
semi-classical behaviour of entropy is reproduced by states that correspond to
all possible triangulations of the Euclidean black hole.Comment: 11 pages LaTeX, 3 eps figures, some minor clarifications added,
result unchange
Artificial Neural Network-based error compensation procedure for low-cost encoders
An Artificial Neural Network-based error compensation method is proposed for
improving the accuracy of resolver-based 16-bit encoders by compensating for
their respective systematic error profiles. The error compensation procedure,
for a particular encoder, involves obtaining its error profile by calibrating
it on a precision rotary table, training the neural network by using a part of
this data and then determining the corrected encoder angle by subtracting the
ANN-predicted error from the measured value of the encoder angle. Since it is
not guaranteed that all the resolvers will have exactly similar error profiles
because of the inherent differences in their construction on a micro scale, the
ANN has been trained on one error profile at a time and the corresponding
weight file is then used only for compensating the systematic error of this
particular encoder. The systematic nature of the error profile for each of the
encoders has also been validated by repeated calibration of the encoders over a
period of time and it was found that the error profiles of a particular encoder
recorded at different epochs show near reproducible behavior. The ANN-based
error compensation procedure has been implemented for 4 encoders by training
the ANN with their respective error profiles and the results indicate that the
accuracy of encoders can be improved by nearly an order of magnitude from
quoted values of ~6 arc-min to ~0.65 arc-min when their corresponding
ANN-generated weight files are used for determining the corrected encoder
angle.Comment: 16 pages, 4 figures. Accepted for Publication in Measurement Science
and Technology (MST
A new alkylated benzoquinone from rhizomes of Iris kumaonensis
A novel alkylated unsaturated p-benzoquinone designated as 3-[(z)-120-heptadecenyl]-
2-hydroxy-5-methoxy-1,4-benzoquinone was isolated from hexane extract of the rhizomes of
Iris kumaonensis and it’s structure was confirmed by extensive spectroscopic analysis, IR, MS,
HREIMS, 1D, 2D NMR and comparison with the literature data of known compounds
Spin-orbit tuned metal-insulator transitions in single-crystal Sr2Ir1-xRhxO4 (0\leqx\leq1)
Sr2IrO4 is a magnetic insulator driven by spin-orbit interaction (SOI)
whereas the isoelectronic and isostructural Sr2RhO4 is a paramagnetic metal.
The contrasting ground states have been shown to result from the critical role
of the strong SOI in the iridate. Our investigation of structural, transport,
magnetic and thermal properties reveals that substituting 4d Rh4+ (4d5) ions
for 5d Ir4+(5d5) ions in Sr2IrO4 directly reduces the SOI and rebalances the
competing energies so profoundly that it generates a rich phase diagram for
Sr2Ir1-xRhxO4 featuring two major effects: (1) Light Rh doping (0\leqx\leq0.16)
prompts a simultaneous and precipitous drop in both the electrical resistivity
and the magnetic ordering temperature TC, which is suppressed to zero at x =
0.16 from 240 K at x=0. (2) However, with heavier Rh doping (0.24< x<0.85
(\pm0.05)) disorder scattering leads to localized states and a return to an
insulating state with spin frustration and exotic magnetic behavior that only
disappears near x=1. The intricacy of Sr2Ir1-xRhxO4 is further highlighted by
comparison with Sr2Ir1-xRuxO4 where Ru4+(4d4) drives a direct crossover from
the insulating to metallic states.Comment: 5 figure
Exotic Gapless Mott Insulators of Bosons on Multi-Leg Ladders
We present evidence for an exotic gapless insulating phase of hard-core
bosons on multi-leg ladders with a density commensurate with the number of
legs. In particular, we study in detail a model of bosons moving with direct
hopping and frustrating ring exchange on a 3-leg ladder at filling.
For sufficiently large ring exchange, the system is insulating along the ladder
but has two gapless modes and power law transverse density correlations at
incommensurate wave vectors. We propose a determinantal wave function for this
phase and find excellent comparison between variational Monte Carlo and density
matrix renormalization group calculations on the model Hamiltonian, thus
providing strong evidence for the existence of this exotic phase. Finally, we
discuss extensions of our results to other -leg systems and to -layer
two-dimensional structures.Comment: 5 pages, 4 figures; v3 is the print version; supplemental material
attache
Evolution of Magnetism in Single-Crystal Honeycomb Iridates
We report the successful synthesis of single-crystals of the layered iridate,
(NaLi)IrO, , and a thorough study of
its structural, magnetic, thermal and transport properties. The new compound
allows a controlled interpolation between NaIrO and LiIrO,
while maintaing the novel quantum magnetism of the honeycomb Ir planes.
The measured phase diagram demonstrates a dramatic suppression of the N\'eel
temperature, , at intermediate suggesting that the magnetic order in
NaIrO and LiIrO are distinct, and that at , the
compound is close to a magnetically disordered phase that has been sought after
in NaIrO and LiIrO. By analyzing our magnetic data with a
simple theoretical model we also show that the trigonal splitting, on the
Ir ions changes sign from NaIrO and LiIrO, and the
honeycomb iridates are in the strong spin-orbit coupling regime, controlled by
\jeff=1/2 moments.Comment: updated version with more dat
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