Spin-glass phase transition and behavior of nonlinear susceptibility in the Sherrington-Kirkpatrick model with random fields

The behavior of the nonlinear susceptibility $\chi_3$ and its relation to the spin-glass transition temperature $T_f$, in the presence of random fields, are investigated. To accomplish this task, the Sherrington-Kirkpatrick model is studied through the replica formalism, within a one-step replica-symmetry-breaking procedure. In addition, the dependence of the Almeida-Thouless eigenvalue $\lambda_{\rm AT}$ (replicon) on the random fields is analyzed. Particularly, in absence of random fields, the temperature $T_f$ can be traced by a divergence in the spin-glass susceptibility $\chi_{\rm SG}$, which presents a term inversely proportional to the replicon $\lambda_{\rm AT}$. As a result of a relation between $\chi_{\rm SG}$ and $\chi_3$, the latter also presents a divergence at $T_f$, which comes as a direct consequence of $\lambda_{\rm AT}=0$ at $T_f$. However, our results show that, in the presence of random fields, $\chi_3$ presents a rounded maximum at a temperature $T^{*}$, which does not coincide with the spin-glass transition temperature $T_f$ (i.e., $T^* > T_f$ for a given applied random field). Thus, the maximum value of $\chi_3$ at $T^*$ reflects the effects of the random fields in the paramagnetic phase, instead of the non-trivial ergodicity breaking associated with the spin-glass phase transition. It is also shown that $\chi_3$ still maintains a dependence on the replicon $\lambda_{\rm AT}$, although in a more complicated way, as compared with the case without random fields. These results are discussed in view of recent observations in the LiHo$_x$Y$_{1-x}$F$_4$ compound.Comment: accepted for publication in PR

Photoassociative ionization of Na inside a storage ring

Motivated by recent interest in low dimensional arrays of atoms, we experimentally investigated the way cold collisional processes are affected by the geometry of the considered atomic sample. More specifically, we studied the case of photoassociative ionization (PAI) both in a storage ring where collision is more unidirectional in character and in a trap with clear undefinition of collision axis. First, creating a ring shaped trap (atomotron) we investigated two-color PAI dependence with intensity and polarization of a probing laser. The intensity dependence of the PAI rate was also measured in a magneto-optical trap presenting equivalent temperature and density conditions. Indeed, the results show that in the ring trap, the value of the PAI rate constant is much lower and does not show evidences of saturation, unlike in the case of the 3D-MOT. Cold atomic collisions in storage ring may represent new possibilities for study.Comment: 5 pages, 5 figures; Accepted by Optics Communicatio

Route to turbulence in a trapped Bose-Einstein condensate

We have studied a Bose-Einstein condensate of $^{87}Rb$ atoms under an oscillatory excitation. For a fixed frequency of excitation, we have explored how the values of amplitude and time of excitation must be combined in order to produce quantum turbulence in the condensate. Depending on the combination of these parameters different behaviors are observed in the sample. For the lowest values of time and amplitude of excitation, we observe a bending of the main axis of the cloud. Increasing the amplitude of excitation we observe an increasing number of vortices. The vortex state can evolve into the turbulent regime if the parameters of excitation are driven up to a certain set of combinations. If the value of the parameters of these combinations is exceeded, all vorticity disappears and the condensate enters into a different regime which we have identified as the granular phase. Our results are summarized in a diagram of amplitude versus time of excitation in which the different structures can be identified. We also present numerical simulations of the Gross-Pitaevskii equation which support our observations.Comment: 6 pages, 3 figure

Functionalizing self-assembled GaN quantum dot superlattices by Eu-implantation

Self-assembled GaN quantum dots (QDs) stacked in superlattices (SL) with AlN spacer layers were implanted with Europium ions to fluences of 1013, 1014, and 1015 cm−2. The damage level introduced in the QDs by the implantation stays well below that of thick GaN epilayers. For the lowest fluence, the structural properties remain unchanged after implantation and annealing while for higher fluences the implantation damage causes an expansion of the SL in the [0001] direction which increases with implantation fluence and is only partly reversed after thermal annealing at 1000 °C. Nevertheless, in all cases, the SL quality remains very good after implantation and annealing with Eu ions incorporated preferentially into near-substitutional cation sites. Eu3+ optical activation is achieved after annealing in all samples. In the sample implanted with the lowest fluence, the Eu3+ emission arises mainly from Eu incorporated inside the QDs while for the higher fluences only the emission from Eu inside the AlN-buffer, capping, and spacer layers is observed. © 2010 American Institute of PhysicsFCT-PTDC/CTM/100756/2008program PESSOA EGIDE/GRICESFCT-SFRH/BD/45774/2008FCT-SFRH/BD/44635/200

Collective excitation of a Bose-Einstein condensate by modulation of the atomic scattering length

We excite the lowest-lying quadrupole mode of a Bose-Einstein condensate by modulating the atomic scattering length via a Feshbach resonance. Excitation occurs at various modulation frequencies, and resonances located at the natural quadrupole frequency of the condensate and at the first harmonic are observed. We also investigate the amplitude of the excited mode as a function of modulation depth. Numerical simulations based on a variational calculation agree with our experimental results and provide insight into the observed behavior.Comment: Submitted to PR

Avaliação de atributos físicos do solo e desenvolvimento da cultivar tangor murcot em latossolo amarelo coeso sob efeito da subsolagem.

Objetivou-se avaliar os atributos físicos do solo sob efeito da subsolagem em Latossolo Amarelo Coeso de tabuleiro costeiro e conseqüências no desenvolvimento do cultivar tangor Murcott. O experimento foi instalado na Fazenda Lagoa do Coco, Litoral Norte do Estado da Bahia. O delineamento experimental foi em blocos ao acaso, com cinco tratamentos e seis repetições: T1- aração + gradagem; T2 - subsolagem com uma haste nas linhas de plantio; T3 - subsolagem cruzada, com uma haste, nas linhas de plantio; T4 - subsolagem com três hastes nas linhas de plantio e T5 - subsolagem cruzada, com três hastes, nas linhas de plantio. As seguintes variáveis foram avaliadas: resistência mecânica do solo à penetração, densidade do solo, crescimento radicular e da parte aérea, produtividade do pomar, abscisão (queda) e peso médio dos frutos. Para todas as variáveis avaliadas, o melhor tratamento de preparo do solo é o T4: a diferença de número e peso total de frutos entre os tratamentos T4 e T1 é de 63% e 83%, respectivamente; a queda de frutos no tratamento T1 é aproximadamente o triplo da observada nos tratamentos T4 e T5, mostrando que a subsolagem possibilita, além de maior produtividade, maior tempo de retenção dos frutos na planta

Applying semantic web technologies to knowledge sharing in aerospace engineering

This paper details an integrated methodology to optimise Knowledge reuse and sharing, illustrated with a use case in the aeronautics domain. It uses Ontologies as a central modelling strategy for the Capture of Knowledge from legacy docu-ments via automated means, or directly in systems interfacing with Knowledge workers, via user-defined, web-based forms. The domain ontologies used for Knowledge Capture also guide the retrieval of the Knowledge extracted from the data using a Semantic Search System that provides support for multiple modalities during search. This approach has been applied and evaluated successfully within the aerospace domain, and is currently being extended for use in other domains on an increasingly large scale

Care causing diagnosis, comorbidities and nutritional status of patients in continuous long term care unit

Introduction: Poor nutritional status has negative implications on prognosis, cost of care, morbidity and mortality. However, when nutritional assessment is not implemented, malnutrition can go untreated. Objectives: The aim of this study was to establish a relationship between care causing diagnosis, existing comorbidities and nutritional status of patients admitted to a long-term care unit. Methods: In the context of Nutrition Day audit, from 2016 to 2018, nutritional status was assessed using Mini Nutritional Assessment. Sociodemographic and anthropometric data, as well as medical history were collected. Results: Sixty-two individuals were included (51.6% male), with a mean age of 7711 years. Mean BMI was 22.94.3kg/m2. Most of the patients were bedridden or in wheelchair (51.6%). A great part of the sample was at risk of malnutrition (40.3%) and 27.4% was malnourished. The majority of the sample showed dementia (75.8%) and 66.2% had depression. A correlation was found between nutritional status and cognitive status(r = 0.445; p = 0.000); and between nutritional status and functional capacity(r = 0.284; p = 0.025). Care causing diagnosis for most of the patients was central nervous system disease (66.1%), followed by heart disease (59.7%), skeletal muscle disease (30.6%) and cancer (17.7%). An association was found between heart disease and malnutrition (p = 0.023). Almost all of the sample was polymedicated (91.9%) and most was taking antypsychotics and/or neuroleptics (71.0%). Conclusions: In this long-term care unit, malnutrition presented a significant prevalence. Cognitive status decline and low functional capacity seem to be correlated with a worse nutritional status. Also, heart disease was associated with malnutrition, meaning that these are significant risk factors for the development of malnutrition. Nutrition Day audit brings awareness to the importance of nutritional care, as well as the need for development of nutritional screening and assessment protocols.info:eu-repo/semantics/publishedVersio