Onset of fluidization in vertically shaken granular material

When granular material is shaken vertically one observes convection, surface fluidization, spontaneous heap formation and other effects. There is a controversial discussion in literature whether there exists a threshold for the Froude number $\Gamma=A_0\omega_0^2/g$ below which these effects cannot be observed anymore. By means of theoretical analysis and computer simulation we find that there is no such single threshold. Instead we propose a modified criterion which coincides with critical Froude number $\Gamma_c=1$ for small driving frequency $\omega_0$.Comment: 7 pages, 5 figure

Coefficient of restitution for elastic disks

We calculate the coefficient of restitution, $\epsilon$, starting from a microscopic model of elastic disks. The theory is shown to agree with the approach of Hertz in the quasistatic limit, but predicts inelastic collisions for finite relative velocities of two approaching disks. The velocity dependence of $\epsilon$ is calculated numerically for a wide range of velocities. The coefficient of restitution furthermore depends on the elastic constants of the material via Poisson's number. The elastic vibrations absorb kinetic energy more effectively for materials with low values of the shear modulus.Comment: 25 pages, 12 Postscript figures, LaTex2

The robustness of carbon fibre members bonded to aluminium connectors in aerial delivery systems

In this paper a framework for robust design solution of an adhesively bonded joint between a composite material and an aluminum connector is developed. To this end, an approach has been developed to automate the process of robust design by linking Ansys workbench and an in-house MATLAB code. The model employed in this study investigated the possibility of joining composite materials to aluminum components which is a problematic process in terms of preparation, implementation, etc. Before designing such a join, it is necessary to fully understand the behaviour of the proposed aluminum connector with the carbon fibre member. To achieve this, the investigation of the adhesive layer’s behaviour and the uncertainties involved in such structures was identified. The behaviour of the adhesive between the carbon fibre composite and the aluminum connector was modelled based on the assumption that this layer acts as a “spring system” within a “cohesive” zone. Initially, the properties of Permabond ET5428 BLACK adhesive were used for validating the finite element model using the obtained test data. A robust design method is then employed to identify the right adhesive for the joint which not only maximizes the debonding force and sliding distance but is also robust with respect to the variation in its mechanical properties. A wide range of adhesive properties have been employed and a robust design technique based on uncertainty analysis is proposed

Structural Ordering and Symmetry Breaking in Cd_2Re_2O_7

Single crystal X-ray diffraction measurements have been carried out on Cd_2Re_2O_7 near and below the phase transition it exhibits at Tc' ~195 K. Cd_2Re_2O_7 was recently discovered as the first, and to date only, superconductor with the cubic pyrochlore structure. Superlattice Bragg peaks show an apparently continuous structural transition at Tc', however the order parameter displays anomalously slow growth to ~Tc'/10, and resolution limited critical-like scattering is seen above Tc'. High resolution measurements show the high temperature cubic Bragg peaks to split on entering the low temperature phase, indicating a (likely tetragonal) lowering of symmetry below Tc'.Comment: 4 pages, 4 figure

Modulation of MUC1 mucin as an escape mechanism of breast cancer cells from autologous cytotoxic T-lymphocytes

MUC1 mucin is known to serve as a target molecule in the killing of breast cancer cells by cytotoxic T-lymphocytes (CTLs). We searched for a possible mechanism allowing tumour cells to escape from autologous CTLs. When the killing of breast cancer cells by autologous lymphocytes was examined in 26 patients with breast cancer, significant tumour cell lysis was observed in 8 patients, whereas virtually no autologous tumour cell lysis was detected in as many as 18 patients. In the patients who showed negligible tumour cell lysis, the autologous tumour cells expressed MUC1-related antigenic epitopes much more weakly than the tumour cells in the patients who exhibited strong cytotoxicity (significant statistically at P< 0.0005–0.0045), suggesting that the unresponsiveness of cancer cells to CTLs observed in these patients was mainly due to loss of MUC1 expression or modulation of its antigenicity. A breast cancer cell line, NZK-1, established from one of the cytotoxicity-negative patients, did not express MUC1 and was resistant to killing by CTLs, while control breast cancer cell lines expressing MUC-1 were readily killed by CTLs. Transfection of NZK-1 cells with MUC1 cDNA induced significant lysis by autologous T-lymphocytes. These results supported the importance of MUC1 mucin in autologous anti-tumour immunity, but suggested that the major escape mechanism of tumour cells from autologous T-lymphocytes is the loss and/or modulation of MUC1 antigenicity on tumour cells, which would limit the effectiveness of possible immunotherapy designed to target the MUC1 mucin. © 2001 Cancer Research Campaign http://www.bjcancer.co

Clustering and Non-Gaussian Behavior in Granular Matter

We investigate the properties of a model of granular matter consisting of $N$ Brownian particles on a line subject to inelastic mutual collisions. This model displays a genuine thermodynamic limit for the mean values of the energy and the energy dissipation. When the typical relaxation time $\tau$ associated with the Brownian process is small compared with the mean collision time $\tau_c$ the spatial density is nearly homogeneous and the velocity probability distribution is gaussian. In the opposite limit $\tau \gg \tau_c$ one has strong spatial clustering, with a fractal distribution of particles, and the velocity probability distribution strongly deviates from the gaussian one.Comment: 4 pages including 3 eps figures, LaTex, added references, corrected typos, minimally changed contents and abstract, to published in Phys.Rev.Lett. (tentatively on 28th of October, 1998

Field‐aligned currents during IMF ∼0

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95012/1/grl14623.pd

Two-dimensional superconductivity at a Mott-Insulator/Band-Insulator interface: LaTiO3/SrTiO3

Transition metal oxides display a great variety of quantum electronic behaviours where correlations often play an important role. The achievement of high quality epitaxial interfaces involving such materials gives a unique opportunity to engineer artificial structures where new electronic orders take place. One of the most striking result in this area is the recent observation of a two-dimensional electron gas at the interface between a strongly correlated Mott insulator LaTiO3 and a band insulator SrTiO3. The mechanism responsible for such a behaviour is still under debate. In particular, the influence of the nature of the insulator has to be clarified. Here we show that despite the expected electronic correlations, LaTiO3/SrTiO3 heterostructures undergo a superconducting transition at a critical temperature Tc=300 mK. We have found that the superconducting electron gas is confined over a typical thickness of 12 nm. We discuss the electronic properties of this system and review the possible scenarios

Angle of Repose and Angle of Marginal Stability: Molecular Dyanmics of Granular Particles

We present an implementation of realistic static friction in molecular dynamics (MD) simulations of granular particles. In our model, to break contacts between two particles, one has to apply a finite amount of force, determined by the Coulomb criterion. Using a two dimensional model, we show that piles generated by avalanches have a {\it finite} angle of repose $\theta_R$ (finite slopes). Furthermore, these piles are stable under tilting by an angle smaller than a non-zero tilting angle $\theta_T$, showing that $\theta_R$ is different from the angle of marginal stability $\theta_{MS}$, which is the maximum angle of stable piles. These measured angles are compared to a theoretical approximation. We also measure $\theta_{MS}$ by continuously adding particles on the top of a stable pile.Comment: 14 pages, Plain Te

Granular Collapse as a Percolation Transition

Inelastic collapse is found in a two-dimensional system of inelastic hard disks confined between two walls which act as an energy source. As the coefficient of restitution is lowered, there is a transition between a state containing small collapsed clusters and a state dominated by a large collapsed cluster. The transition is analogous to that of a percolation transition. At the transition the number of clusters n_s of size s scales as $n_s \sim s^{-\tau}$ with $\tau \approx 2.7$.Comment: 10 pages revtex, 5 figures, accepted by Phys Rev E many changes and corrections from previous submissio