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

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 $H<H_{c1}$, (ii) a fully polarised phase for $H>H_{c2}$, and (iii) a Luttinger liquid magnetic phase in the regime $H_{c1}<H<H_{c2}$. 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

Probabilistic models of information retrieval based on measuring the divergence from randomness

We introduce and create a framework for deriving probabilistic models of Information Retrieval. The models are nonparametric models of IR obtained in the language model approach. We derive term-weighting models by measuring the divergence of the actual term distribution from that obtained under a random process. Among the random processes we study the binomial distribution and Bose--Einstein statistics. We define two types of term frequency normalization for tuning term weights in the document--query matching process. The first normalization assumes that documents have the same length and measures the information gain with the observed term once it has been accepted as a good descriptor of the observed document. The second normalization is related to the document length and to other statistics. These two normalization methods are applied to the basic models in succession to obtain weighting formulae. Results show that our framework produces different nonparametric models forming baseline alternatives to the standard tf-idf model