2,499 research outputs found
Dimerized ground states in spin-S frustrated systems
We study a family of frustrated anti-ferromagnetic spin- systems with a
fully dimerized ground state. This state can be exactly obtained without the
need to include any additional three-body interaction in the model. The
simplest members of the family can be used as a building block to generate more
complex geometries like spin tubes with a fully dimerized ground state. After
present some numerical results about the phase diagram of these systems, we
show that the ground state is robust against the inclusion of weak disorder in
the couplings as well as several kinds of perturbations, allowing to study some
other interesting models as a perturbative expansion of the exact one. A
discussion on how to determine the dimerization region in terms of quantum
information estimators is also presented. Finally, we explore the relation of
these results with a the case of the a 4-leg spin tube which recently was
proposed as the model for the description of the compound
CuClDCSO, delimiting the region of the parameter space
where this model presents dimerization in its ground state.Comment: 10 pages, 9 figure
Phase diagram study of a dimerized spin-S zig-zag ladder
The phase diagram of a frustrated spin- zig-zag ladder is studied through
different numerical and analytical methods. We show that for arbitrary ,
there is a family of Hamiltonians for which a fully-dimerized state is an exact
ground state, being the Majumdar-Ghosh point a particular member of the family.
We show that the system presents a transition between a dimerized phase to a
N\'eel-like phase for , and spiral phases can appear for large . The
phase diagram is characterized by means of a generalization of the usual Mean
Field Approximation (MFA). The novelty in the present implementation is to
consider the strongest coupled sites as the unit cell. The gap and the
excitation spectrum is analyzed through the Random Phase Approximation (RPA).
Also, a perturbative treatment to obtain the critical points is discussed.
Comparisons of the results with numerical methods like DMRG are also presented.Comment: 14 pages, 6 figures. Some typos were corrected, and notation was
clarifie
Quantum phases in the frustrated Heisenberg model on the bilayer honeycomb lattice
We use a combination of analytical and numerical techniques to study the
phase diagram of the frustrated Heisenberg model on the bilayer honeycomb
lattice. Using the Schwinger boson description of the spin operators followed
by a mean field decoupling, the magnetic phase diagram is studied as a function
of the frustration coupling and the interlayer coupling .
The presence of both magnetically ordered and disordered phases is
investigated by means of the evaluation of ground-state energy, spin gap, local
magnetization and spin-spin correlations. We observe a phase with a spin gap
and short range N\'eel correlations that survives for non-zero
next-nearest-neighbor interaction and interlayer coupling. Furthermore, we
detect signatures of a reentrant behavior in the melting of N\'eel phase and
symmetry restoring when the system undergoes a transition from an on-layer
nematic valence bond crystal phase to an interlayer valence bond crystal phase.
We complement our work with exact diagonalization on small clusters and
dimer-series expansion calculations, together with a linear spin wave approach
to study the phase diagram as a function of the spin , the frustration and
the interlayer couplings.Comment: 10 pages, 9 figure
Design of the Target Dump Injection Segmented (TDIS) in the framework of the High Luminosity Large Hadron Collider (HL-LHC) project
The High Luminosity Large Hadron Collider (HL-LHC) Project at CERN calls for increasing beam brightness and intensity. In this scenario, most equipment has to be redesigned and rebuilt. In particular, beam intercepting devices (such as dumps, collimators, absorbers and scrapers) have to withstand impact or scraping of the new intense HL-LHC beams without failure. Furthermore, minimizing the electromagnetic beam-device interactions is also a key design driver since they can lead to beam instabilities and excessive thermo-mechanical loading of devices. In this context, the present study assesses the conceptual design quality of the new LHC injection protection absorber, the Target Dump Injection Segmented (TDIS), from an electromagnetic and thermo-mechanical perspective. This contribution analyzes the thermo-mechanical response of the device considering two cases: an accidental beam impact scenario and another accidental scenario with complete failure of the RFcontacts.
In addition, this paper presents the preliminary results from the simulation of the energy deposited by the two counter-rotating beams circulating in the device
Structural studies of mesoporous ZrO-CeO and ZrO-CeO/SiO mixed oxides for catalytical applications
In this work the synthesis of ZrO-CeO and
ZrO-CeO/SiO were developed, based on the process to form
ordered mesoporous materials such as SBA-15 silica. The triblock copolymer
Pluronic P-123 was used as template, aiming to obtain crystalline single phase
walls and larger specific surface area, for future applications in catalysis.
SAXS and XRD results showed a relationship between ordered pores and the
material crystallization. 90% of CeO leaded to single phase homogeneous
ceria-zirconia solid solution of cubic fluorite structure (Fmm). The
SiO addition improved structural and textural properties as well as the
reduction behavior at lower temperatures, investigated by XANES measurements
under H atmosphere
Changes in land use in Mato Grosso do Sul
Among the species cultivated in Mato Grosso do Sul, the area with soybeans is larger than that only for pasture cultivation. This work was developed in fourteen municipalities of the state. Based on information from the Brazilian Institute of Geography and Statistics (IBGE), the evolution of the area occupied by soybean, pasture and sugarcane in these municipalities was analysed. In particular, the area cultivated with soybeans has shown constant and significant growth. On the other hand, the pasture area has been continuously decreasing, especially in Ponta Porã, Maracaju and Rio Brilhante. The areas previously occupied with pastures are giving way to soy and sugarcane cultivation
Nitrogênio e regulador de crescimento no algodoeiro no sistema plantio direto.
bitstream/item/39666/1/PA-6-1998.pd
Algodoeiro em sistema plantio direto.
Tradicionalmente, para o cultivo do algodoeiro, o solo é preparado utilizando-se vários implementos e operações. Os implementos mais utilizados para o preparo do solo são: grade pesada (uma vez), grade leve (duas a três vezes) e, em muitos casos, ainda é utilizada uma grade intermediária. Este sistema de manejo leva à degradação das propriedades físicas, químicas e biológicas do solo e, paulatinamente, diminui o potencial produtivo do mesmobitstream/item/24415/1/COT2006118.pdfDocumento on-line
- …