Bose-Einstein condensates with attractive 1/r interaction: The case of self-trapping

Amplifying on a proposal by O'Dell et al. for the realization of Bose-Einstein condensates of neutral atoms with attractive $1/r$ interaction, we point out that the instance of self-trapping of the condensate, without external trap potential, is physically best understood by introducing appropriate "atomic" units. This reveals a remarkable scaling property: the physics of the condensate depends only on the two parameters $N^2 a/a_u$ and $\gamma/N^2$, where $N$ is the particle number, $a$ the scattering length, $a_u$ the "Bohr" radius and $\gamma$ the trap frequency in atomic units. We calculate accurate numerical results for self-trapping wave functions and potentials, for energies, sizes and peak densities, and compare with previous variational results. As a novel feature we point out the existence of a second solution of the extended Gross-Pitaevskii equation for negative scattering lengths, with and without trapping potential, which is born together with the ground state in a tangent bifurcation. This indicates the existence of an unstable collectively excited state of the condensate for negative scattering lengths.Comment: 7 pages, 7 figures, to appear in Phys. Rev.

Solitary Waves Under the Competition of Linear and Nonlinear Periodic Potentials

In this paper, we study the competition of linear and nonlinear lattices and its effects on the stability and dynamics of bright solitary waves. We consider both lattices in a perturbative framework, whereby the technique of Hamiltonian perturbation theory can be used to obtain information about the existence of solutions, and the same approach, as well as eigenvalue count considerations, can be used to obtained detailed conditions about their linear stability. We find that the analytical results are in very good agreement with our numerical findings and can also be used to predict features of the dynamical evolution of such solutions.Comment: 13 pages, 4 figure

Impurity correlations in dilute Kondo alloys

The single impurity Kondo model is often used to describe metals with dilute concentrations (n_i) of magnetic impurities. Here we examine how dilute the impurities must be for this to be valid by developing a virial expansion in impurity density. The O(n_i^2) term is determined from results on the 2-impurity Kondo problem by averaging over the RKKY coupling. The non-trivial fixed point of the 2-impurity problem could produce novel singularities in the heat capacity of dilute alloys at O(n_i^2).Comment: 6 pages, no figure

The spin angular gradient approximation in the density functional theory

A spin angular gradient approximation for the exchange correlation magnetic field in the density functional formalism is proposed. The usage of such corrections leads to a consistent spin dynamical approach beyond the local approximation. The proposed technique does not contain any approximations for the form of potential and can be used in modern full potential band structure methods. The obtained results indicate that the direct 'potential' exchange in 3d magnets is rather small compared to the indirect 'kinetic' exchange, thus justifies the dynamical aspect of the local density approximation in 3d metals

Creating and observing N-partite entanglement with atoms

The Mermin inequality provides a criterion for experimentally ruling out local-realistic descriptions of multiparticle systems. A violation of this inequality means that the particles must be entangled, but does not, in general, indicate whether N-partite entanglement is present. For this, a stricter bound is required. Here we discuss this bound and use it to propose two different schemes for demonstrating N-partite entanglement with atoms. The first scheme involves Bose-Einstein condensates trapped in an optical lattice and the second uses Rydberg atoms in microwave cavities.Comment: 12 pages, 4 figure

Analytic perturbation theory in QCD and Schwinger's connection between the beta-function and the spectral density

We argue that a technique called analytic perturbation theory leads to a well-defined method for analytically continuing the running coupling constant from the spacelike to the timelike region, which allows us to give a self-consistent definition of the running coupling constant for timelike momentum. The corresponding $\beta$-function is proportional to the spectral density, which confirms a hypothesis due to Schwinger.Comment: 11 pages, 2 figure

A New Solution of the Yang-Baxter Equation Related to the Adjoint Representation of UqB2U_{q}B_{2}

A new solution of the Yang-Baxter equation, that is related to the adjoint representation of the quantum enveloping algebra $U_{q}B_{2}$, is obtained by fusion formulas from a non-standard solution.Comment: 16 pages (Latex), Preprint BIHEP-TH-93-3

Xrn1/Pacman affects apoptosis and regulates expression of hid and reaper

Programmed cell death, or apoptosis, is a highly conserved cellular process that is crucial for tissue homeostasis under normal development as well as environmental stress. Misregulation of apoptosis is linked to many developmental defects and diseases such as tumour formation, autoimmune diseases and neurological disorders. In this paper, we show a novel role for the exoribonuclease Pacman/Xrn1 in regulating apoptosis. Using Drosophila wing imaginal discs as a model system, we demonstrate that a null mutation in pacman results in small imaginal discs as well as lethality during pupation. Mutant wing discs show an increase in the number of cells undergoing apoptosis, especially in the wing pouch area. Compensatory proliferation also occurs in these mutant discs, but this is insufficient to compensate for the concurrent increase in apoptosis. The phenotypic effects of the pacman null mutation are rescued by a deletion that removes one copy of each of the pro-apoptotic genes reaper, hid and grim, demonstrating that pacman acts through this pathway. The null pacman mutation also results in a significant increase in the expression of the pro-apoptotic mRNAs, hid and reaper, with this increase mostly occurring at the post-transcriptional level, suggesting that Pacman normally targets these mRNAs for degradation. Our results uncover a novel function for the conserved exoribonuclease Pacman and suggest that this exoribonuclease is important in the regulation of apoptosis in other organisms

Magnetic Resonance of the Intrinsic Defects of the Spin-Peierls Magnet CuGeO3

ESR of the pure monocrystals of CuGeO3 is studied in the frequency range 9-75 GHz and in the temperature interval 1.2-25 K. The splitting of the ESR line into several spectral components is observed below 5 K, in the temperature range where the magnetic susceptibility is suppressed by the spin-Peierls dimerization. The analysis of the magnetic resonance signals allows one to separate the signals of the S=1/2- and S=1 defects of the spin-Peierls phase. The value of g-factor of these signals is close to that of the Cu-ion. The additional line of the magnetic resonance is characterized by an anomalous value of the g-factor and by the threshold-like increase of the microwave susceptibility when the microwave power is increasing. The ESR signals are supposingly attributed to two types of the planar magnetic defects, arising at the boundaries of the domains of the spin-Peierls state with the different values of the phase of the dimerization.Comment: LATEX-text, 12 PS-figures, typos corrected, LATEX-style change