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

Qualidade fisiológica de sementes de milheto armazenadas.

A cultura do trigo tem grande importância comercial, contudo ainda são escassos, resultados científicos referente ao uso de herbicidas nesta cultura. Em termos de mercado é notório a pequena quantidade de produtos recomendados para o controle de plantas daninhas em pós-emergência desta cultura, e limitadas são as informações sobre os efeitos que estes causam. Neste contexto, o objetivo do presente trabalho foi avaliar o desempenho agronômico e a qualidade fisiológica das sementes sob o efeito da aplicação de doses crescentes de Metsulfuron methyl (Ally) em estádios de desenvolvimento diferentes, assumindo que altas doses de Ally podem ser utilizadas em dois estádios de desenvolvimento e supondo que o emprego de altas doses em combinação com o estádio de desenvolvimento possa afetar a planta. Com este intuito foi conduzido um ensaio a campo, no Município de Marialva - PR, com delineamento em blocos completos casualizados, com quatro repetições, em que os tratamentos foram compostos por cinco doses do herbicida Ally O; 30; 60; 90; 120g i.a. ha; aplicadas em dois estádios da cultura: 4 e 10.4. As variáveis avaliadas foram: produtividade, massa de mil sementes, germinação e vigor (pela primeira contagem do teste de germinação). A partir dos resultados obtidos, pode-se inferir que: o herbicida Ally aplicado em altas doses no período reprodutivo tende a diminuir a produtividade (P<O, 1 O) e o vigor (P<0,03) de suas sementes, porém aplicações no vegetativo não apresentam efeitos significativos ai, 5 e 10% de probabilidade, com relação aos caracteres observados aqui.Edição dos Resumos do XVI Congresso Brasileiro de Sementes, Curitiba, PR, set. 2003

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

Quantum Critical Point in the Spin Glass-Kondo Transition in Heavy Fermion Systems

The Kondo-Spin Glass competition is studied in a theoretical model of a Kondo lattice with an intra-site Kondo type exchange interaction treated within the mean field approximation, an inter-site quantum Ising exchange interaction with random couplings among localized spins and an additional transverse field in the x direction, which represents a simple quantum mechanism of spin flipping. We obtain two second order transition lines from the spin-glass state to the paramagnetic one and then to the Kondo state. For a reasonable set of the different parameters, the two second order transition lines do not intersect and end in two distinct QCP.Comment: 20 pages; 1 figure; to appear in Physical Review

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

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