6,415 research outputs found
Ising t-J model close to half filling: A Monte Carlo study
Within the recently proposed doped-carrier representation of the projected
lattice electron operators we derive a full Ising version of the t-J model.
This model possesses the global discrete Z_2 symmetry as a maximal spin
symmetry of the Hamiltonian at any values of the coupling constants, t and J.
In contrast, in the spin anisotropic limit of the t-J model, usually referred
to as the t-J_z model, the global SU(2) invariance is fully restored at J_z=0,
so that only the spin-spin interaction has in that model the true Ising form.
We discuss a relationship between those two models and the standard isotropic
t-J model. We show that the low-energy quasiparticles in all three models share
the qualitatively similar properties at low doping and small values of J/t. The
main advantage of the proposed Ising t-J model over the t-J_z one is that the
former allows for the unbiased Monte Carlo calculations on large clusters of up
to 10^3 sites. Within this model we discuss in detail the destruction of the
antiferromagnetic order by doping as well as the interplay between the AF order
and hole mobility. We also discuss the effect of the exchange interaction and
that of the next nearest neighbour hoppings on the destruction of the AF order
at finite doping. We show that the short-range AF order is observed in a wide
range of temperatures and dopings, much beyond the boundaries of the AF phase.
We explicitly demonstrate that the local no double occupancy constraint plays
the dominant role in destroying the magnetic order at finite doping. Finally, a
role of inhomogeneities is discussed.Comment: 24 pages, 10 figure
The structure of chromospheres around late-type giants and supergiants
Observations alpha Tau (K5III) and beta Gru (M2II) made at high resolution are used to confirm line identifications of features blended at low resolution. The high resolution spectra allow selected pairs of lines to be used to find the electron density and the opacity. Methods for determining these factors and the usual emission measure are presented. The electron density and opacity can be used together with the emission measure to place constraints on the structure of the atmosphere. The line formation processes are briefly discussed. Photo-excitation by strong lines appears to be important in these late type atmospheres
Ward Identities and chiral anomalies for coupled fermionic chains
Coupled fermionic chains are usually described by an effective model written
in terms of bonding and anti-bonding spinless fields with linear dispersion in
the vicinities of the respective Fermi points. We derive for the first time
exact Ward Identities (WI) for this model, proving the existence of chiral
anomalies which verify the Adler-Bardeen non-renormalization property. Such WI
are expected to play a crucial role in the understanding of the thermodynamic
properties of the system. Our results are non-perturbative and are obtained
analyzing Grassmann functional integrals by means of Constructive Quantum Field
Theory methods.Comment: TeX file, 26 pages, 7 figures. Published version, new section added
to answer referee remarks and derive the Ward Identites, no modifications in
the main resul
Psicologia ambiental e agroecologia: apropriação do espaço por famÃlias de agricultores.
Trabalhos anteriores (Bassani, Silveira e Ferraz, 2003; Bassani, Ferraz e Silveira, 2004)assinalaram contribuições da Psicologia Ambiental para a Agroecologia, através de metodologias participativas. Este trabalho é um estudo piloto sobre apropriação de espaço e apego ao lugar por famÃlias de agricultores do municÃpio de Araras (SP). O modelo dual de apropriação de espaço (Pol, 2002) envolve ação/transformação do espaço e identificação simbólica e, a partir deste processo, identificam-se caracterÃsticas do apego ao lugar. Resultados indicam diferenças entre as famÃlias nos processos de ação/transformação. Do ponto de vista simbólico, não há diferenças entre as famÃlias: são mantidos sÃmbolos de identidade da famÃlia e da região. Discute-se o papel de polÃticas públicas na apropriação de espaço dos agricultores e suas famÃlias
Métodos participativos e agroecologia familiar.
O presente artigo propõe a reflexão sobre a abordagem participativa relacionada ao ambiente complexo da prática agroecológica. Considera-se, que pesquisas participativas assentadas em arranjos metodológicos desta natureza destacam as condições reais de produção familiar e permitem apreender os distintos modos de vida e aspectos particulares presentes na reprodução das famÃlias rurais. Ademais, seus resultados possibilitam aos agricultores revalorizar suas potencialidades e intensificar o atendimento das suas próprias necessidades
The modulated spin liquid: a new paradigm for URuSi
We argue that near a Kondo breakdown critical point, a spin liquid with
spatial modulations can form. Unlike its uniform counterpart, we find that this
occurs via a second order phase transition. The amount of entropy quenched when
ordering is of the same magnitude as for an antiferromagnet. Moreover, the two
states are competitive, and at low temperatures are separated by a first order
phase transition. The modulated spin liquid we find breaks symmetry, as
recently seen in the hidden order phase of URuSi. Based on this, we
suggest that the modulated spin liquid is a viable candidate for this unique
phase of matter.Comment: 4 pages, 2 figure
Thymic Squamous Cell Carcinoma? Do you confirm this diagnosis?
Introduction
In dogs thymic carcinoma is considered rare and distinguishes itself from thymoma by its cytologically malignant features, extensive local invasion, and a substantial potential for metastasis. Surgical excision is the treatment of choice for most thymic tumours, with the exception of lymphoma.
Medical History
A 9 years old cross-breed male dog was presented due to cough and respiratory distress with duration of 4 weeks. The animal presented with inspiratory dyspnea and cyanosis. A mass, dorsal to the pharynx, was diagnosed after clinical and radiographical examination, suspected of thyroid neoplasia. Cytology was performed and revealed cells consistent with malignancy, apparently carcinoma with high parameters of aggressiveness. As a form of treatment and to obtain a definitive diagnosis, was decided to surgical removed the mass which measured 7.8x3.7x3.5cm.
Material and Methods
The sample was fixed in 10 % buffered formalin solution for histological evaluation and sent to the Anatomic Pathology Laboratory of the Agrarian Superior School of Viseu, in Portugal, for histological evaluation.
Results
Microscopic examination revealed that we were in presence of a lymphoid organ, with peculiar features, namely a small to intermediate-sized lymphoid cells, "starry-sky" pattern and rounded eosinophilic perivascular arrangements resembling Hassall's corpuscles. Concomitantly, typical features of squamous cell carcinoma were evident.
Discussion and Conclusion
In conclusion, based on its histological features, the authors suggested the diagnosis of Thymic Squamous Cell Carcinoma with an unusual location. Thymic tumours in dogs are predominantly located in the anterior mediastinum but they may extend from the neck to the posterior mediastinum.This work was supported by Portuguese Foundation for Science and Technology, Center for Studies in Education, Technologies and by Health and by strategic project PEst-OE/CED/UI4016/201
Methodologies and technological innovations for low-carbon agriculture monitoring and planning for the ABC Plan governance support - Geo ABC.
Ecosystem services integrity on different phyto-ecologic zones of the Amazon State, Brazil - expert and probabilistic Bayesian model approaches.
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