Testing of powders for sensitivity to air effect segregation

A loss of blend homogeneity through handling operations can have a major influence on the mechanical properties of sintered products. Plant optimisation to minimise the potential for segregation of blends can be undertaken through an audit of handling operations combined with an evaluation of the materials that are handled through the process. The correct identification of the mechanism of segregation is essential to support strategies to implement the most efficient and cost-effective counter measures. In support of this type of industrial activity, a piece of test apparatus has recently been developed to provide measurements of segregation potential for powders (metal and mineral) that are prone to loss of homogeneity (by composition or particle size) when subjected to counter-directional air displacements through equipment. The test equipment is described and examples given of its output in industrial application

Centrifugal tester versus a novel design to measure particle adhesion strength and investigation of effect of physical characteristics (size, shape, density) of food particles on food surfaces

A new experimental procedure has been established and a novel Impact Adhesion Tester has been designed and constructed. In the experiment, the amount of powder detached from one side of a crisp substrate by the impact forces (48, 77 and 102 g-force) generated by the tester was measured. In addition, a centrifuge tester was used along with specially designed tubes for substrate housing. Centrifugal speed applied varied from 300 up to 4000 rpm. Crisps (3 cm diameter and 3 mm thickness) and wood veneer pieces (1 x 2 cm and 2 mm thickness) were used as test substrates and salt particles (63–125, 125–180, and 180–250 lm) were used as coating material after applying oil on the surface. The comparison between results obtained from two methods was discussed. In addition, spherical and crushed glass particles (150–180, and 212–250 lm) were used to investigate the effect of shape on adhesion strength. Significant changes in adhesion strength have been observed for particles with different sizes and shapes

Brookfield powder flow tester - Results of round robin tests with CRM-116 limestone powder

A low cost powder flowability tester for industry has been developed at The Wolfson Centre for Bulk Solids Handling Technology, University of Greenwich in collaboration with Brookfield Engineering and four food manufacturers: Cadbury, Kerry Ingredients, GSK and United Biscuits. Anticipated uses of the tester are primarily for quality control and new product development, but it can also be used for storage vessel design. This paper presents the preliminary results from ‘round robin’ trials undertaken with the powder flow tester using the BCR limestone (CRM-116) standard test material. The mean flow properties have been compared to published data found in the literature for the other shear testers

Reliable low-cost fabrication of low-loss Al2O3:Er3+Al_2O_3:Er^{3+} waveguides with 5.4-dB optical gain

A reliable and reproducible deposition process for the fabrication of $Al_2O_3$ waveguides with losses as low as 0.1 dB/cm has been developed. The thin films are grown at ~ 5 nm/min deposition rate and exhibit excellent thickness uniformity within 1% over 50times50 mm2 area and no detectable $OH^{-}$ incorporation. For applications of the $Al_2O_3$ films in compact, integrated optical devices, a high-quality channel waveguide fabrication process is utilized. Planar and channel propagation losses as low as 0.1 and 0.2 dB/cm, respectively, are demonstrated. For the development of active integrated optical functions, the implementation of rare-earth-ion doping is investigated by cosputtering of erbium during the $Al_2O_3$ layer growth. Dopant levels between 0.2-5times $1020 cm^{-3}$ are studied. At $Er^{3+}$ concentrations of interest for optical amplification, a lifetime of the 4I13/2 level as long as 7 ms is measured. Gain measurements over 6.4-cm propagation length in a 700-nm-thick $Al_2O_3:Er^{3+}$ channel waveguide result in net optical gain over a 41-nm-wide wavelength range between 1526-1567 nm with a maximum of 5.4 dB at 1533 n

Bistability and macroscopic quantum coherence in a BEC of ^7Li

We consider a Bose-Einstein condensate (BEC) of $^7Li$ in a situation where the density undergoes a symmetry breaking in real space. This occurs for a suitable number of condensed atoms in a double well potential, obtained by adding a standing wave light field to the trap potential. Evidence of bistability results from the solution of the Gross-Pitaevskii equation. By second quantization, we show that the classical bistable situation is in fact a Schr\"odinger cat (SC) and evaluate the tunneling rate between the two SC states. The oscillation between the two states is called MQC (macroscopic quantum coherence); we study the effects of losses on MQC.Comment: 8 pages, 11 figures. e-mail: [email protected]

Effect of anharmonicities in the critical number of trapped condensed atoms with attractive two-body interaction

We determine the quantitative effect, in the maximum number of particles and other static observables, due to small anharmonic terms added to the confining potential of an atomic condensed system with negative two-body interaction. As an example of how a cubic or quartic anharmonic term can affect the maximum number of particles, we consider the trap parameters and the results given by Roberts et al. [Phys. Rev. Lett. 86, 4211 (2001)]. However, this study can be easily transferred to other trap geometries to estimate anharmonic effects.Comment: Total of 5 pages, 3 figures and 1 table. To appear in Phys. Rev.

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

Thermodynamics of an interacting trapped Bose-Einstein gas in the classical field approximation

We present a convenient technique describing the condensate in dynamical equilibrium with the thermal cloud, at temperatures close to the critical one. We show that the whole isolated system may be viewed as a single classical field undergoing nonlinear dynamics leading to a steady state. In our procedure it is the observation process and the finite detection time that allow for splitting the system into the condensate and the thermal cloud.Comment: 4 pages, 4 eps figures, final versio

Self-Trapping, Quantum Tunneling and Decay Rates for a Bose Gas with Attractive Nonlocal Interaction

We study the Bose-Einstein condensation for a cloud of $^7$Li atoms with attractive nonlocal (finite-range) interaction in a harmonic trap. In addition to the low-density metastable branch, that is present also in the case of local interaction, a new stable branch appears at higher densities. For a large number of atoms, the size of the cloud in the stable high-density branch is independent of the trap size and the atoms are in a macroscopic quantum self-trapped configuration. We analyze the macroscopic quantum tunneling between the low-density metastable branch and the high-density one by using the istanton technique. Moreover we consider the decay rate of the Bose condensate due to inelastic two- and three-body collisions.Comment: 5 pages, 4 figures, submitted to Phys. Rev.

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