Three-dimensional solitons in coupled atomic-molecular Bose-Einstein condensates

We present a theoretical analysis of three-dimensional (3D) matter-wave solitons and their stability properties in coupled atomic and molecular Bose-Einstein condensates (BECs). The soliton solutions to the mean-field equations are obtained in an approximate analytical form by means of a variational approach. We investigate soliton stability within the parameter space described by the atom-molecule conversion coupling, the atom-atom s-wave scattering, and the bare formation energy of the molecular species. In terms of ordinary optics, this is analogous to the process of sub- or second-harmonic generation in a quadratic nonlinear medium modified by a cubic nonlinearity, together with a phase mismatch term between the fields. While the possibility of formation of multidimensional spatiotemporal solitons in pure quadratic media has been theoretically demonstrated previously, here we extend this prediction to matter-wave interactions in BEC systems where higher-order nonlinear processes due to interparticle collisions are unavoidable and may not be neglected. The stability of the solitons predicted for repulsive atom-atom interactions is investigated by direct numerical simulations of the equations of motion in a full 3D lattice. Our analysis also leads to a possible technique for demonstrating the ground state of the Schrodinger-Newton and related equations that describe Bose-Einstein condensates with nonlocal interparticle forces.

Mechanics of raceway hysteresis in a packed bed

When a gas is introduced at high velocity through a nozzle into a packed bed, it creates a raceway in the packed bed. It has been found that the raceway size is larger when it is formed by decreasing the gas velocity from its highest value than when it is formed by increasing the gas velocity. This phenomenon is known as raceway hysteresis. A hypothesis has been oroposed to explain the hysteresis phenomenon based on a force-balance approach which includes frictional, bed-weight, and pressure forces. According to this hypothesis, the frictional force acts in different directions when the raceway is expanding and contracting. In this article, the entire packed bed has been divided into radial and Cartesian co-ordinate systems, and the forces acting on the raceway have been solved analytically for a simplified one-dimensional case. Based on the force-balance approach, a general equation has been obtained to predict the diameter of the raceway for increasing And decreasing velocities. A reasonable agreement has been found between the theoretical predictions and experimental observations. The model has also been compared with published experimental and plant data. The hysteresis mechanism in the packed beds can be described reasonably by taking into consideration the direction of frictional forces for the increasing- and decreasin-velocity cases. The effects of the particleshape factor and void fraction on the raceway hysteresis are examined.

Joining forces - Combining cognition-targeted motor control training with group or individual pain physiology education: A successful treatment for chronic low back pain

Chronic unremittent low back pain (LBP) is characterised by cognitive barriers to treatment. Combining a motor control training approach with individualised education about pain physiology is effective in this group of patients. This randomized comparative trial (i) evaluates an approach to motor control acquisition and training that considers the complexities of the relationship between pain and motor output, and (ii) compares the efficacy and cost of individualized and group pain physiology education. After an "ongoing usual treatment" period, patients participated in a 4-week motor control and pain physiology education program. Patients received four one-hour individualized education sessions (IE) or one 4-hour group lecture (GE). Both groups reduced pain (numerical rating scale) and disability (Roland Morris Disability Questionnaire). IE showed bigger decreases, which were maintained at 12 months (P < 0.05 for all). The combined motor control and education approach is effective. Although group education imparts a lesser effect, it may be more cost-efficient. [ABSTRACT FROM AUTHOR]

The impact of market forces on the sustainability of the biotechnology industry

his paper contains a warning for investors, executives, analysts and scientists about the sustainability of the biotechnology industry. The study upon which the paper is based examines the impact of market forces on the biotechnology industry and argues that the short-term focus of market driven policies and practices impacts on the sustainability of firms operating in the industry. The market is represented by the National Association of Securities Dealers, Automated Quotations Market (NASDAQ), considered to be one of the vehicles of the promotion of ''new economy'' companies and principles. Through the application of bibliometric data (using both refereed and non-refereed papers), matched with the long term tracking of the NASDAQ Biotechnology Index, the authors provide a clear indication that the short-term investment thinking is leading an industry that is characterised by long R&D cycles. There is an incompatibility between the shorter-term investment considerations and the long-term scientific developments the biotechnology industry is attempting to achieve. Graphs and illustrations are provided to portray the comparative data.

Tailoring surface properties to build colloidal diagnostic devices: Controlling interparticle associations

The ability to control the surface properties and subsequent colloidal stability of dispersed particles has widespread applicability in many fields. Sub-micrometer fluorescent silica particles (reporters) can be used to actively encode the combinatorial synthesis of peptide libraries through interparticle association. To achieve these associations, the surface chemistry of the small fluorescent silica reporters is tailored to encourage robust adhesion to large silica microparticles onto which the peptides are synthesized. The interparticle association must withstand a harsh solvent environment multiple synthetic and washing procedures, and biological screening buffers. The encoded support beads were exposed to different solvents used for peptide synthesis, and different solutions used for biological screening including phosphate buffered saline (PBS), 2-[N-morpholino]ethane sulfonic acid (VIES) and a mixture of MES and N-(3-dimethyl-aminopropyl)-N'-ethylcarbodiimide (EDC). The number of reporters remaining adhered to the support bead was quantified after each step. The nature of the associations were explored and tested to optimize the efficiency of these phenomena. Results presented illustrate the influence of the surface functionality and polyelectrolyte modification of the reporters. These parameters were investigated through zeta potential and X-ray photoelectron spectroscopy.

Forces from highly focused laser beams: Modeling, measurement and application to refractive index measurements

The optical forces in optical tweezers can be robustly modeled over a broad range of parameters using generalsed Lorenz–Mie theory. We describe the procedure, and show how the combination of experimental measurement of properties of the trap coupled with computational modeling, can allow unknown parameters of the particle—in this case, the refractive index—to be determined.