279 research outputs found
Doping a Mott insulator with orbital degrees of freedom
We study the effects of hole doping on one-dimensional Mott insulators with
orbital degrees of freedom. We describe the system in terms of a generalized
t-J model. At a specific point in parameter space the model becomes integrable
in analogy to the one-band supersymmetric t-J model. We use the Bethe ansatz to
derive a set of nonlinear integral equations which allow us to study the
thermodynamics exactly. Moving away from this special point in parameter space
we use the density-matrix renormalization group applied to transfer matrices to
study the evolution of various phases of the undoped system with doping and
temperature. Finally, we study a one-dimensional version of a realistic model
for cubic titanates which includes the anisotropy of the orbital sector due to
Hund's coupling. We find a transition from a phase with antiferromagnetically
correlated spins to a phase where the spins are fully ferromagnetically
polarized, a strong tendency towards phase separation at large Hund's coupling,
as well as the possibility of an instability towards triplet superconductivity
Classification of Solutions to the Plane Extremal Distance Problem for Bodies With Smooth Boundaries
Naval Postgraduate School PANSAT: Lessons Learned
AIAA Space 2001 - Conference and Exposition, Albuquerque, NM, August 28-30, 2001The Petite Amateur Navy Satellite (PANSAT) was
launched aboard the STS-95 Discovery Shuttle on 29
October 1998. PANSAT was inserted into a circular,
low-Earth orbit at an altitude of 550 km and 28.45°
inclination on 30 October 1998. PANSAT continues to
operate and support the educational mission at NPS
even after reaching its two-year design life. The
research aspect also continues with the analysis of the
accumulated telemetry data, in terms of how well the
spacecraft operated over the mission design life.
However, the store-and-forward mission using direct
sequence spread spectrum was never realized
Controlled Longitudinal Emittance Blow-Up in the CERN PS
The longitudinal emittance of the bunches in the CERN PS must be increased before transition crossing to avoid beam loss due to a fast vertical instability. This controlled blow-up is essential for all high-intensity beams in the PS, including those for transfer to the LHC. The higher harmonic 200MHz RF system (six cavities) used for this blow-up has to generate a total RF voltage which, for the most demanding blow-up, is comparable to the voltage of the main RF cavities. The system is presently subject to a major upgrade and a possible reduction in the number of higher harmonic RF cavities installed is under consideration. To determine the minimum required, detailed simulations and machine development studies to optimize the longitudinal blow-up have been performed. Further options to produce the required longitudinal emittance using other RF systems are also analyzed. The results obtained for the different scenarios for the longitudinal blow-up are presented and compared in this paper
Measuring Global Similarity between Texts
We propose a new similarity measure between texts which, contrary to the
current state-of-the-art approaches, takes a global view of the texts to be
compared. We have implemented a tool to compute our textual distance and
conducted experiments on several corpuses of texts. The experiments show that
our methods can reliably identify different global types of texts.Comment: Submitted to SLSP 201
Commissioning and performance of a phase-compensated optical link for the AWAKE experiment at CERN
In this work, we analyze the performance of the solution adopted for the
compensation of the phase drift of a 3 km optical fiber link used for the AWAKE
experiment at CERN. The link is devoted to transmit the reference signals used
to synchronize the SPS beam with the experiment to have a fixed phase relation,
regardless of the external conditions of the electronics and the link itself.
The system has been operating for more than a year without observed drift in
the beam phases. Specific measurements have proven that the jitter introduced
by the system is lower than 0.6 ps and the maximum phase drift of the link is
at the picosecond level.Comment: Poster presented at LLRF Workshop 2017 (LLRF2017, arXiv:1803.07677
Fifty years of spellchecking
A short history of spellchecking from the late 1950s to the present day, describing its development through dictionary lookup, affix stripping, correction, confusion sets, and edit distance to the use of gigantic databases
Integrable models and quantum spin ladders: comparison between theory and experiment for the strong coupling ladder compounds
(abbreviated) This article considers recent advances in the investigation of
the thermal and magnetic properties of integrable spin ladder models and their
applicability to the physics of real compounds. The ground state properties of
the integrable two-leg spin-1/2 and the mixed spin-(1/2,1) ladder models at
zero temperature are analyzed by means of the Thermodynamic Bethe Ansatz.
Solving the TBA equations yields exact results for the critical fields and
critical behaviour. The thermal and magnetic properties of the models are
investigated in terms of the recently introduced High Temperature Expansion
method, which is discussed in detail. It is shown that in the strong coupling
limit the integrable spin-1/2 ladder model exhibits three quantum phases: (i) a
gapped phase in the regime , (ii) a fully polarised phase for
, and (iii) a Luttinger liquid magnetic phase in the regime
. The critical behaviour in the vicinity of the critical
points is of the Pokrovsky-Talapov type. The temperature-dependent thermal and
magnetic properties are directly evaluated from the exact free energy
expression and compared to known experimental results for a range of strong
coupling ladder compounds. Similar analysis of the mixed spin-(1/2,1) ladder
model reveals a rich phase diagram, with a 1/3 and a full saturation
magnetisation plateau within the strong antiferromagnetic rung coupling regime.
For weak rung coupling, the fractional magnetisation plateau is diminished and
a new quantum phase transition occurs. The phase diagram can be directly
deduced from the magnetisation curve obtained from the exact result derived
from the HTE. The thermodynamics of the spin-orbital model with different
single-ion anisotropies is also investigated.Comment: 90 pages, 33 figures, extensive revisio
Reference Measurements of the Longitudinal Impedance in the CERN SPS
First reference measurements of the longitudinal impedance were made with beam in the SPS machine in 1999 to quantify the results of the impedance reduction programme, completed in 2001. The 2001 data showed that the low-frequency inductive impedance had been reduced by a factor 2.5 and that bunch lengthening due to the microwave instability was absent up to the ultimate LHC bunch intensity. Measurements of the quadrupole frequency shift with intensity in the following years suggest a significant increase in impedance (which nevertheless remains below the 1999 level) due to the installation of eight extraction kickers for beam transfer to the LHC. The experimental results are compared with expectations based on the known longitudinal impedance of the SPS
Nonlinear integral equations for the thermodynamics of the sl(4)-symmetric Uimin-Sutherland model
We derive a finite set of nonlinear integral equations (NLIE) for the
thermodynamics of the one-dimensional sl(4)-symmetric Uimin-Sutherland model.
Our NLIE can be evaluated numerically for arbitrary finite temperature and
chemical potentials. We recover the NLIE for sl(3) as a limiting case. In
comparison to other recently derived NLIE, the evaluation at low temperature
poses no problem in our formulation. The model shows a rich ground-state phase
diagram. We obtain the critical fields from the T to zero limit of our NLIE. As
an example for the application of the NLIE, we give numerical results for the
SU(4) spin-orbital model. The magnetic susceptibility shows divergences at
critical fields in the low-temperature limit and logarithmic singularities for
zero magnetic field.Comment: 32 pages, 7 figures; references added, minor corrections, final
versio
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