Critical number of atoms for attractive Bose-Einstein condensates with cylindrically symmetrical traps

We calculated, within the Gross-Pitaevskii formalism, the critical number of atoms for Bose-Einstein condensates with two-body attractive interactions in cylindrical traps with different frequency ratios. In particular, by using the trap geometries considered by the JILA group [Phys. Rev. Lett. 86, 4211 (2001)], we show that the theoretical maximum critical numbers are given approximately by $N_c = 0.55 ({l_0}/{|a|})$. Our results also show that, by exchanging the frequencies $\omega_z$ and $\omega_\rho$, the geometry with $\omega_\rho < \omega_z$ favors the condensation of larger number of particles. We also simulate the time evolution of the condensate when changing the ground state from $a=0$ to $a<0$ using a 200ms ramp. A conjecture on higher order nonlinear effects is also added in our analysis with an experimental proposal to determine its signal and strength.Comment: (4 pages, 2 figures) To appear in Physical Review

Stability of the trapped nonconservative Gross-Pitaevskii equation with attractive two-body interaction

The dynamics of a nonconservative Gross-Pitaevskii equation for trapped atomic systems with attractive two-body interaction is numerically investigated, considering wide variations of the nonconservative parameters, related to atomic feeding and dissipation. We study the possible limitations of the mean field description for an atomic condensate with attractive two-body interaction, by defining the parameter regions where stable or unstable formation can be found. The present study is useful and timely considering the possibility of large variations of attractive two-body scattering lengths, which may be feasible in recent experiments.Comment: 6 pages, 5 figures, submitted to Physical Review

Influence of thermal fluctuations on quantum phase transitions in one-dimensional disordered systems: Charge density waves and Luttinger liquids

The low temperature phase diagram of 1D weakly disordered quantum systems like charge or spin density waves and Luttinger liquids is studied by a \emph{full finite temperature} renormalization group (RG) calculation. For vanishing quantum fluctuations this approach is amended by an \emph{exact} solution in the case of strong disorder and by a mapping onto the \emph{Burgers equation with noise} in the case of weak disorder, respectively. At \emph{zero} temperature we reproduce the quantum phase transition between a pinned (localized) and an unpinned (delocalized) phase for weak and strong quantum fluctuations, respectively, as found previously by Fukuyama or Giamarchi and Schulz. At \emph{finite} temperatures the localization transition is suppressed: the random potential is wiped out by thermal fluctuations on length scales larger than the thermal de Broglie wave length of the phason excitations. The existence of a zero temperature transition is reflected in a rich cross-over phase diagram of the correlation functions. In particular we find four different scaling regions: a \emph{classical disordered}, a \emph{quantum disordered}, a \emph{quantum critical} and a \emph{thermal} region. The results can be transferred directly to the discussion of the influence of disorder in superfluids. Finally we extend the RG calculation to the treatment of a commensurate lattice potential. Applications to related systems are discussed as well.Comment: 19 pages, 7 figure

Porphyrin biosynthesis. VII. Porphyrinogen carboxy-lyase from avian erythrocytes. Purification and properties

1. 1. Uroporphyrinogen carboxy-lyase (EC 4.1.1.d), the enzyme catalysing the decaroxylation of uroporphyrinogen to coproporphyrinogen, has been isolated from normal chicken erythrocytes. The enzyme was purified 220-fold with a yield of 24% from haemolysate supernatant by DEAE-cellulose batch treatment, (NH4)2SO4 fractionation and chromatography on DEAE-cellulose. 2. 2. The purified material appears to be homogeneous in polyacrylamide gel disc electrophoresis. 3. 3. The enzyme was heat labile and inhibited by sodium salt; the activity was enhanced by EDTA, GSH and boiled rat-liver extract. 4. 4. The influence of these chemical and physical agents on the removal of the first and second carboxyl groups from uroporphyrinogen was compared; the second group was more susceptible to these agents. 5. 5. The possibility that one or several enzymes were involved in the stepwise decarboxylation of uroporphyrinogen is discussed. 6. 6. The general name of porphyrinogen carboxy-lyase for the enzyme system is proposed because of the different porphyrinogens it can decarboxylate. © 1970.Fil:Tomio, J.M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:García, R.C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:San Martín De Viale, L.C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.Fil:Grinstein, M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

O poder da caneta: a Medida Provisória no processo legislativo estadual

A Medida Provisória (MP) brasileira é um dos instrumentos legislativos mais poderosos nas mãos do Presidente da República para alterar unilateralmente o status quo. Apesar de o judiciário ter reconhecido a competência dos governadores para instituir e adotar a MP, esta existe apenas em seis estados. O artigo procura explicar a não adoção deste instrumento legislativo pela maioria dos estados. Enfatiza-se a escassa ou marginal relevância que é dada à MP pelo governador nos seis casos que a adotaram. Defende-se, aqui, que os governadores, diferentemente dos presidentes, não necessitam de mais um instrumento legislativo ou da ampliação da delegação de prerrogativas legislativas para garantir sua agenda frente a seus respectivos legislativos, já que com ou sem poder de decreto estadual os governadores controlariam a já limitada agenda decisória nos estados.<br>The Brazilian Provisional Measure (MP) is one of the most powerful legislative instruments in the hands of the President to unilaterally change the status quo. Although the judiciary (STF) has recognized the competence of Governors to establish and adopt the MP only six states attribute the prerogative to edit MP until 2010. This article seeks to explain the non-adoption of this legislative instrument by most states emphasizing the low or marginal relevance that is given to the MP by the Governor in the six cases that adopted it. It is argued here that the Governors, unlike Presidents, do not require another legislative instrument or expanding the delegation of legislative powers to ensure their legislative agenda forward their respective State Legislative Assemblies, because with or without decree power the State Governors would control the limited decisional agenda in the states