Anomalous Expansion of Attractively Interacting Fermionic Atoms in an Optical Lattice

Strong correlations can dramatically modify the thermodynamics of a quantum many-particle system. Especially intriguing behaviour can appear when the system adiabatically enters a strongly correlated regime, for the interplay between entropy and strong interactions can lead to counterintuitive effects. A well known example is the so-called Pomeranchuk effect, occurring when liquid 3He is adiabatically compressed towards its crystalline phase. Here, we report on a novel anomalous, isentropic effect in a spin mixture of attractively interacting fermionic atoms in an optical lattice. As we adiabatically increase the attraction between the atoms we observe that the gas, instead of contracting, anomalously expands. This expansion results from the combination of two effects induced by pair formation in a lattice potential: the suppression of quantum fluctuations as the attraction increases, which leads to a dominant role of entropy, and the progressive loss of the spin degree of freedom, which forces the gas to excite additional orbital degrees of freedom and expand to outer regions of the trap in order to maintain the entropy. The unexpected thermodynamics we observe reveal fundamentally distinctive features of pairing in the fermionic Hubbard model.Comment: 6 pages (plus appendix), 6 figure

Relative dispersion in fully developed turbulence: The Richardson's Law and Intermittency Corrections

Relative dispersion in fully developed turbulence is investigated by means of direct numerical simulations. Lagrangian statistics is found to be compatible with Richardson description although small systematic deviations are found. The value of the Richardson constant is estimated as $C_2 \simeq 0.55$, in a close agreement with recent experimental findings [S. Ott and J. Mann J. Fluid Mech. {\bf 422}, 207 (2000)]. By means of exit-time statistics it is shown that the deviations from Richardson's law are a consequence of Eulerian intermittency. The measured Lagrangian scaling exponents require a set of Eulerian structure function exponents $\zeta_{p}$ which are remarkably close to standard ones known for fully developed turbulence

Turbulent Friction in Rough Pipes and the Energy Spectrum of the Phenomenological Theory

The classical experiments on turbulent friction in rough pipes were performed by J. Nikuradse in the 1930's. Seventy years later, they continue to defy theory. Here we model Nikuradse's experiments using the phenomenological theory of Kolmog\'orov, a theory that is widely thought to be applicable only to highly idealized flows. Our results include both the empirical scalings of Blasius and Strickler, and are otherwise in minute qualitative agreement with the experiments; they suggest that the phenomenological theory may be relevant to other flows of practical interest; and they unveil the existence of close ties between two milestones of experimental and theoretical turbulence.Comment: Accepted for publication in PRL; 4 pages, 4 figures; revised versio

Integrable model for interacting electrons in metallic grains

We find an integrable generalization of the BCS model with non-uniform Coulomb and pairing interaction. The Hamiltonian is integrable by construction since it is a functional of commuting operators; these operators, which therefore are constants of motion of the model, contain the anisotropic Gaudin Hamiltonians. The exact solution is obtained diagonalizing them by means of Bethe Ansatz. Uniform pairing and Coulomb interaction are obtained as the ``isotropic limit'' of the Gaudin Hamiltonians. We discuss possible applications of this model to a single grain and to a system of few interacting grains.Comment: 4 pages, revtex. Revised version to be published in Phys. Rev. Let

Universality in Turbulence: an Exactly Soluble Model

The present note contains the text of lectures discussing the problem of universality in fully developed turbulence. After a brief description of Kolmogorov's 1941 scaling theory of turbulence and a comparison between the statistical approach to turbulence and field theory, we discuss a simple model of turbulent advection which is exactly soluble but whose exact solution is still difficult to analyze. The model exhibits a restricted universality. Its correlation functions contain terms with universal but anomalous scaling but with non-universal amplitudes typically diverging with the growing size of the system. Strict universality applies only after such terms have been removed leaving renormalized correlators with normal scaling. We expect that the necessity of such an infrared renormalization is a characteristic feature of universality in turbulence.Comment: 31 pages, late

Vortex Plastic Motion in Twinned Superconductors

We present simulations, without electrodynamical assumptions, of $B(x,y,H(t)), M(H(t))$, and $J_c(H(t))$, in hard superconductors, for a variety of twin-boundary pinning potential parameters, and for a range of values of the density and strength of the pinning sites. We numerically solve the overdamped equations of motion of up to 10^4 flux-gradient-driven vortices which can be temporarily trapped at $\sim 10^6$ pinning centers. These simulations relate macroscopic measurements (e.g., M(H), ``flame'' shaped $B(x,y)$ profiles) with the underlying microscopic pinning landscape and the plastic dynamics of individual vortices

On the Origins of Starburst and Post-Starburst Galaxies in Nearby Clusters

HST WFPC2 images in B (F450W) and I (F814W) have been obtained for three starburst (SB) and two post-starburst (PSB) galaxies in the Coma cluster, and for three such galaxies in the cluster DC2048-52. V (F555W) and I images for an additional PSB galaxy in Coma have been extracted from the archive. Seven of these galaxies were previously classified as E/S0 on the basis of ground-based images, one as Sa, and the other as an irregular. The HST images reveal these SB/PSB galaxies to be heterogeneous in morphology. Nevertheless a common theme is that many of them, especially the SB galaxies, tend to have centralized spiral structure that appears simply as a bright ``bulge''on ground-based images. In addition, while some PSB galaxies exhibit distinct spiral structure, on the whole they have smoother morphologies than the SB galaxies. The morphologies and luminosity profiles are generally consistent with substantial starbursts in the form of centralized spiral structure (the SB galaxies) which fade into smoother morphologies (the PSB galaxies), with lingering spectroscopic evidence for past central starbursts. An important point is that the PSB galaxies retain disks, i.e, they have not evolved into spheroidal systems.Comment: 32 pages, 10 figures including 3 jpg images. To appear in the January 1999 Astronomical Journa

The (LATTICE) QCD Potential and Running Coupling: How to Accurately Interpolate between Multi-Loop QCD and the String Picture

We present a simple parameterization of a running coupling constant, defined via the static potential, that interpolates between 2-loop QCD in the UV and the string prediction in the IR. Besides the usual \Lam-parameter and the string tension, the coupling depends on one dimensionless parameter, determining how fast the crossover from UV to IR behavior occurs (in principle we know how to take into account any number of loops by adding more parameters). Using a new Ansatz for the LATTICE potential in terms of the continuum coupling, we can fit quenched and unquenched Monte Carlo results for the potential down to ONE lattice spacing, and at the same time extract the running coupling to high precision. We compare our Ansatz with 1-loop results for the lattice potential, and use the coupling from our fits to quantitatively check the accuracy of 2-loop evolution, compare with the Lepage-Mackenzie estimate of the coupling extracted from the plaquette, and determine Sommer's scale $r_0$ much more accurately than previously possible. For pure SU(3) we find that the coupling scales on the percent level for $\beta\geq 6$.Comment: 47 pages, incl. 4 figures in LaTeX [Added remarks on correlated vs. uncorrelated fits in sect. 4; corrected misprints; updated references.

Continuity Culture: A Key Factor for Building Resilience and Sound Recovery Capabilities

This article investigates the extent to which Jordanian service organizations seek to establish continuity culture through testing, training, and updating of their business continuity plans. A survey strategy was adopted in this research. Primary and secondary data were used. Semistructured interviews were conducted with five senior managers from five large Jordanian service organizations registered with the Amman Stock Exchange. The selection of organizations was made on the basis of simple random sampling. Interviews targeted the headquarters only in order to obtain a homogenous sample. Three out of five organizations could be regarded as crisis prepared and have better chances for recovery. The other two organizations exhibited characteristics of standard practice that only emphasizes the recovery aspect of business continuity management (BCM), while paying less attention to establishing resilient cultures and embedding BCM. The findings reveal that the ability to recover following major incidents can be improved by embedding BCM in the culture of the organization and by making BCM an enterprise-wide process. This is one of few meticulous studies that have been undertaken in the Middle East and the first in Jordan to investigate the extent to which service organizations focus on embedding BCM in the organizational culture