Matter wave quantum dots (anti-dots) in ultracold atomic Bose-Fermi mixtures

The properties of ultracold atomic Bose-Fermi mixtures in external potentials are investigated and the existence of gap solitons of Bose-Fermi mixtures in optical lattices demonstrated. Using a self-consistent approach we compute the energy spectrum and show that gap solitons can be viewed as matter wave realizations of quantum dots (anti-dots) with the bosonic density playing the role of trapping (expulsive) potential for the fermions. The fermionic states trapped in the condensate are shown to be at the bottom of the Fermi sea and therefore well protected from thermal decoherence. Energy levels, filling factors and parameters dependence of gap soliton quantum dots are also calculated both numerically and analytically.Comment: Extended version of talk given at the SOLIBEC conference, Almagro, Spain, 8-12 February 2005. To be published on Phys.Rev.

Hierarchy of boundary driven phase transitions in multi-species particle systems

Interacting systems with $K$ driven particle species on a open chain or chains which are coupled at the ends to boundary reservoirs with fixed particle densities are considered. We classify discontinuous and continuous phase transitions which are driven by adiabatic change of boundary conditions. We build minimal paths along which any given boundary driven phase transition (BDPT) is observed and reveal kinetic mechanisms governing these transitions. Combining minimal paths, we can drive the system from a stationary state with all positive characteristic speeds to a state with all negative characteristic speeds, by means of adiabatic changes of the boundary conditions. We show that along such composite paths one generically encounters $Z$ discontinuous and $2(K-Z)$ continuous BDPTs with $Z$ taking values $0\leq Z\leq K$ depending on the path. As model examples we consider solvable exclusion processes with product measure states and $K=1,2,3$ particle species and a non-solvable two-way traffic model. Our findings are confirmed by numerical integration of hydrodynamic limit equations and by Monte Carlo simulations. Results extend straightforwardly to a wide class of driven diffusive systems with several conserved particle species.Comment: 12 pages, 11 figure

Small-amplitude excitations in a deformable discrete nonlinear Schroedinger equation

A detailed analysis of the small-amplitude solutions of a deformed discrete nonlinear Schr\"{o}dinger equation is performed. For generic deformations the system possesses "singular" points which split the infinite chain in a number of independent segments. We show that small-amplitude dark solitons in the vicinity of the singular points are described by the Toda-lattice equation while away from the singular points are described by the Korteweg-de Vries equation. Depending on the value of the deformation parameter and of the background level several kinds of solutions are possible. In particular we delimit the regions in the parameter space in which dark solitons are stable in contrast with regions in which bright pulses on nonzero background are possible. On the boundaries of these regions we find that shock waves and rapidly spreading solutions may exist.Comment: 18 pages (RevTex), 13 figures available upon reques

Coating thickness and coverage effects on the forces between silica nanoparticles in water

The structure and interactions of coated silica nanoparticles have been studied in water using molecular dynamics simulations. For 5 nm diameter amorphous silica nanoparticles we studied the effects of varying the chain length and grafting density of polyethylene oxide (PEO) on the nanoparticle coating's shape and on nanoparticle-nanoparticle effective forces. For short ligands of length $n=6$ and $n=20$ repeat units, the coatings are radially symmetric while for longer chains ($n=100$) the coatings are highly anisotropic. This anisotropy appears to be governed primarily by chain length, with coverage playing a secondary role. For the largest chain lengths considered, the strongly anisotropic shape makes fitting to a simple radial force model impossible. For shorter ligands, where the coatings are isotropic, we found that the force between pairs of nanoparticles is purely repulsive and can be fit to the form $(R/2r_\text{core}-1)^{-b}$ where $R$ is the separation between the center of the nanoparticles, $r_\text{core}$ is the radius of the silica core, and $b$ is measured to be between 2.3 and 4.1.Comment: 20 pages, 6 figure

Percutaneously Inserted AngioVac Suction Thrombectomy for the Treatment of Filter-Related Iliocaval Thrombosis

In the setting of acute iliocaval thrombosis due to reversible causes, thrombus removal is preferred by many in the management of inferior vena cava (IVC) thrombosis as it is thought likely to minimize the long-term complications of chronic venous insufficiency and post-thrombotic syndrome. When catheter-directed thrombolysis is not a viable or effective option, the treatment options are limited. We present the case of a 56-year-old hospitalized patient with a permanent IVC filter that had been inserted 10 years prior at an outside hospital with severe, incapacitating right leg swelling for which amputation was considered. The patient underwent suction thrombectomy after failure of thrombolysis. The patient’s presenting symptoms of right lower extremity swelling and pain improved upon discharge. In our single case, unassisted suction thrombectomy with percutaneously placed cannulae is an effective and safe method for the treatment of permanent IVC filter-related iliocaval thrombosis in cases refractory to catheter-directed thrombolysis

Fiat Money and the Distribution of Incomes and Wealth

Under a fiat money system, the money supply is subject to the human will. It therefore tends to grow faster than under a commodity money system. We analyse the implications of this fact for the distribution of incomes, and especially for the distribution of wealth. We argue that fiat money systems tend to increase the gap between incomes and wealth and also tend to leverage income differences into even greater differences of wealth.

Discrete Nonlinear Schrodinger Equations with arbitrarily high order nonlinearities

A class of discrete nonlinear Schrodinger equations with arbitrarily high order nonlinearities is introduced. These equations are derived from the same Hamiltonian using different Poisson brackets and include as particular cases the saturable discrete nonlinear Schrodinger equation and the Ablowitz-Ladik equation. As a common property, these equations possess three kinds of exact analytical stationary solutions for which the Peierls-Nabarro barrier is zero. Several properties of these solutions, including stability, discrete breathers and moving solutions, are investigated

A cross-country analysis of climate shocks and smallholder food insecurity

Future climate changes will affect smallholder farmers in the developing world, posing threats to household food security. Nevertheless, there remains limited comparable evidence across multiple countries and regions regarding the global extent of climate shocks affecting smallholder food security. We examine data from 5,299 household surveys across 15 countries in Latin America, Africa and South Asia to assess the extent of climate shocks and their association with food insecurity, as well as what strategies may help buffer against climate shocks. We find that 71% of households reported experiencing a climate shock in the previous five years. Fifty-four percent reported experiencing food insecurity during one or more months annually. A multilevel statistical model estimated factors correlated with food insecurity as well as factors correlated with food insecurity among households that had experienced a climate shock. Households that reported experiencing a climate shock were 1.73 times more likely to be food insecure. As well, larger and poorer households were associated with higher odds of food insecurity while using pesticides, keeping large livestock, and being more educated are associated with lower odds of food insecurity. Among households that had experienced a climate shock, additional factors are correlated with lower odds of food insecurity when compared to otherwise similar households: use of fertilizers, pesticides, veterinary medicines, large livestock, and household assets. Together, these results demonstrate the extent of existing climate shocks affecting smallholder farmers and how interventions may potentially support adaptation and reduce food insecurity