7,010 research outputs found
Ferrimagnetic spin-1/2 chain of alternating Ising and Heisenberg spins in arbitrarily oriented magnetic field
The ferrimagnetic spin-1/2 chain composed of alternating Ising and Heisenberg
spins in an arbitrarily oriented magnetic field is exactly solved using the
spin-rotation transformation and the transfer-matrix method. It is shown that
the low-temperature magnetization process depends basically on a spatial
orientation of the magnetic field. A sharp stepwise magnetization curve with a
marked intermediate plateau, which emerges for the magnetic field applied along
the easy-axis direction of the Ising spins, becomes smoother and the
intermediate plateau shrinks if the external field is tilted from the easy-axis
direction. The magnetization curve of a polycrystalline system is also
calculated by performing powder averaging of the derived magnetization formula.
The proposed spin-chain model brings an insight into high-field magnetization
data of 3d-4f bimetallic polymeric compound Dy(NO_3)(DMSO)_2Cu(opba)(DMSO)_2,
which provides an interesting experimental realization of the ferrimagnetic
chain composed of two different but regularly alternating spin-1/2 magnetic
ions Dy^{3+} and Cu^{2+} that are reasonably approximated by the notion of
Ising and Heisenberg spins, respectively.Comment: 11 pages, 6 figure
Feedback-free optical cavity with self-resonating mechanism
We demonstrated the operation of a high finesse optical cavity without
utilizing an active feedback system to stabilize the resonance. The effective
finesse, which is a finesse including the overall system performance, of the
cavity was measured to be , and the laser power stored in
the cavity was kW, which is approximately 187,000 times greater
than the incident power to the cavity. The stored power was stabilized with a
fluctuation of , and we confirmed continuous cavity operation for more
than two hours. This result has the potential to trigger an innovative
evolution for applications that use optical resonant cavities such as compact
photon sources with laser-Compton scattering or cavity enhanced absorption
spectroscopy.Comment: 5 pages, 7 figure
Observation of a Transient Magnetization Plateau in a Quantum Antiferromagnet on the Kagome Lattice
The magnetization process of an S=1/2 antiferromagnet on the kagome lattice,
[Cu_3(titmb)_2(OCOCH_3)_6]H_2O {titmb= 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6
trimethylbenzene} has been measured at very low temperatures in both pulsed and
steady fields. We have found a new dynamical behavior in the magnetization
process: a plateau at one third of the saturation magnetization appears in the
pulsed field experiments for intermediate sweep rates of the magnetic field and
disappears in the steady field experiments. A theoretical analysis using exact
diagonalization yields J_1=-19K and J_2=6K, for the nearest neighbor and second
nearest neighbor interactions, respectively. This set of exchange parameters
explains the very low saturation field and the absence of the plateau in the
thermodynamic equilibrium as well as the two-peak feature in the magnetic heat
capacity. Supported by numerical results we argue that a dynamical order by
disorder phenomenon could explain the transient appearance of the 1/3 plateau
in pulsed field experiments.Comment: 7 pages, 5 figure
Right-veering diffeomorphisms of compact surfaces with boundary II
We continue our study of the monoid of right-veering diffeomorphisms on a
compact oriented surface with nonempty boundary, introduced in [HKM2]. We
conduct a detailed study of the case when the surface is a punctured torus; in
particular, we exhibit the difference between the monoid of right-veering
diffeomorphisms and the monoid of products of positive Dehn twists, with the
help of the Rademacher function. We then generalize to the braid group B_n on n
strands by relating the signature and the Maslov index. Finally, we discuss the
symplectic fillability in the pseudo-Anosov case by comparing with the work of
Roberts [Ro1,Ro2].Comment: 25 pages, 5 figure
Principal Component Analysis of Cavity Beam Position Monitor Signals
Model-independent analysis (MIA) methods are generally useful for analysing
complex systems in which relationships between the observables are non-trivial
and noise is present. Principle Component Analysis (PCA) is one of MIA methods
allowing to isolate components in the input data graded to their contribution
to the variability of the data. In this publication we show how the PCA can be
applied to digitised signals obtained from a cavity beam position monitor
(CBPM) system on the example of a 3-cavity test system installed at the
Accelerator Test Facility 2 (ATF2) at KEK in Japan. We demonstrate that the PCA
based method can be used to extract beam position information, and matches
conventional techniques in terms of performance, while requiring considerably
less settings and data for calibration
Changes in impacts of climate extremes: Human systems and ecosystems
In this chapter, two different types of impacts on human and ecological systems are examined: (i) impacts of extreme weather and climate events; and (ii) extreme impacts triggered by less-than-extreme weather or climate events (in combination with non-climatic factors, such as high exposure and/or vulnerability). Where data are available, impacts are examined from sectoral and regional perspectives
Quasi-elastic neutron scattering in the high-field phase of a Haldane antiferromagnet
Inelastic neutron scattering experiments on the Haldane-gap quantum
antiferromagnet NDMAP are performed in magnetic fields below and above the
critical field Hc at which the gap closes. Quasi-elastic neutron scattering is
found for H>Hc indicating topological excitations in the high field phase.Comment: Added to discussion section. v2: Updated figure
Near-infrared Brightness of the Galilean Satellites Eclipsed in Jovian Shadow: A New Technique to Investigate Jovian Upper Atmosphere
We have discovered that Europa, Ganymede and Callisto are bright around 1.5
{\mu}m even when not directly lit by sunlight, based on observations from the
Hubble Space Telescope and the Subaru Telescope. The observations were
conducted with non-sidereal tracking on Jupiter outside of the field of view to
reduce the stray light subtraction uncertainty due to the close proximity of
Jupiter. Their eclipsed luminosity was - of their uneclipsed
brightness, which is low enough that this phenomenon has been undiscovered
until now. In addition, Europa in eclipse was <1/10 of the others at 1.5
{\mu}m, a potential clue to the origin of the source of luminosity. Likewise,
Ganymede observations were attempted at 3.6 {\mu}m by the Spitzer Space
Telescope but it was not detected, suggesting a significant wavelength
dependence. The reason why they are luminous even when in the Jovian shadow is
still unknown, but forward-scattered sunlight by haze in the Jovian upper
atmosphere is proposed as the most plausible candidate. If this is the case,
observations of these Galilean satellites while eclipsed by the Jovian shadow
provide us a new technique to investigate Jovian atmospheric composition, and
investigating the transmission spectrum of Jupiter by this method is important
for investigating the atmosphere of extrasolar giant planets by transit
spectroscopy.Comment: 7 pages, 3 figures, accepted to Ap
Persistent superfluid phase in a three-dimensional quantum XY model with ring exchange
We present quantum Monte Carlo simulation results on a quantum S=1/2 XY model
with ring exchange (the J-K model) on a three-dimensional simple cubic lattice.
We first characterize the ground state properties of the pure XY model,
obtaining estimations for the energy, spin stiffness and spin susceptibility at
T=0 in the superfluid phase. With the ring exchange, we then present simulation
data on small lattices which suggests that the superfluid phase persists to
very large values of the ring exchange K, without signatures of a phase
transition. We comment on the consequences of this result for the search for
various exotic phases in three dimensions.Comment: 4 pages, 4 figure
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