Speckle visibility spectroscopy and variable granular fluidization

We introduce a dynamic light scattering technique capable of resolving motion that changes systematically, and rapidly, with time. It is based on the visibility of a speckle pattern for a given exposure duration. Applying this to a vibrated layer of glass beads, we measure the granular temperature and its variation with phase in the oscillation cycle. We observe several transitions involving jammed states, where the grains are at rest during some portion of the cycle. We also observe a two-step decay of the temperature on approach to jamming.Comment: 4 pages, 4 figures, experimen

Scaling Behavior in Shaving Cream

The coarsening of a three-dimensional foam is studied with multiple light-scattering techniques. Scaling behavior is observed with the average bubble diameter growing in time as tz where z=0.45±0.05. Changes in the packing conditions during coarsening give rise to a dynamical process that also exhibits temporal scaling. Neighboring bubbles undergo sudden structural rearrangement events at a rate per unit volume that decays as t−y where y=2.0±0.2

Avalanche statistics and time-resolved grain dynamics for a driven heap

We probe the dynamics of intermittent avalanches caused by steady addition of grains to a quasi-two dimensional heap. To characterize the time-dependent average avalanche flow speed v(t), we image the top free surface. To characterize the grain fluctuation speed dv(t), we use Speckle-Visibility Spectroscopy. During an avalanche, we find that the fluctuation speed is approximately one-tenth the average flow speed, and that these speeds are largest near the beginning of an event. We also find that the distribution of event durations is peaked, and that event sizes are correlated with the time interval since the end of the previous event. At high rates of grain addition, where successive avalanches merge into smooth continuous flow, the relationship between average and fluctuation speeds changes to dv Sqrt[v]

Study of effects of fuel properties in turbine-powered business aircraft

Increased interest in research and technology concerning aviation turbine fuels and their properties was prompted by recent changes in the supply and demand situation of these fuels. The most obvious change is the rapid increase in fuel price. For commercial airplanes, fuel costs now approach 50 percent of the direct operating costs. In addition, there were occasional local supply disruptions and gradual shifts in delivered values of certain fuel properties. Dwindling petroleum reserves and the politically sensitive nature of the major world suppliers make the continuation of these trends likely. A summary of the principal findings, and conclusions are presented. Much of the material, especially the tables and graphs, is considered in greater detail later. The economic analysis and examination of operational considerations are described. Because some of the assumptions on which the economic analysis is founded are not easily verified, the sensitivity of the analysis to alternates for these assumptions is examined. The data base on which the analyses are founded is defined in a set of appendices

Scaling of Transient Hydrodynamic Interactions in Concentrated Suspensions

The mean-square displacement 〈Δr2(τ)〉 of particles in concentrated suspensions is measured at times sufficiently short to observe the transient nature of hydrodynamic interactions. For all volume fractions φ, the velocity autocorrelation function decays as a power law R(τ)∼τ−3/2. A remarkable scaling with φ is observed for the time-dependent self-diffusion coefficient Ds(τ)=〈Δr2(τ)〉/6τ: If Ds(τ) is scaled by its asymptotic value and if time is scaled by a viscous time inversely proportional to the shear viscosity of the suspension, all the data fall onto a single master curve

Resolving long-range spatial correlations in jammed colloidal systems using photon correlation imaging

We introduce a new dynamic light scattering method, termed photon correlation imaging, which enables us to resolve the dynamics of soft matter in space and time. We demonstrate photon correlation imaging by investigating the slow dynamics of a quasi two-dimensional coarsening foam made of highly packed, deformable bubbles and a rigid gel network formed by dilute, attractive colloidal particles. We find the dynamics of both systems to be determined by intermittent rearrangement events. For the foam, the rearrangements extend over a few bubbles, but a small dynamical correlation is observed up to macroscopic length scales. For the gel, dynamical correlations extend up to the system size. These results indicate that dynamical correlations can be extremely long-ranged in jammed systems and point to the key role of mechanical properties in determining their nature.Comment: Published version (Phys. Rev. Lett. 102, 085702 (2009)) The Dynamical Activity Mapsprovided as Supplementary Online Material are also available on http://w3.lcvn.univ-montp2.fr/~lucacip/dam/movies.ht

Microrheology probes length scale dependent rheology

We exploit the power of microrheology to measure the viscoelasticity of entangled F-actin solutions at different length scales from 1 to 100 mu m over a wide frequency range. We compare the behavior of single probe-particle motion to that of the correlated motion of two particles. By varying the average length of the filaments, we identify fluctuations that dissipate diffusively over the filament length. These provide an important relaxation mechanism of the elasticity between 0.1 and 30 rad/sec

Grain Boundary Scars and Spherical Crystallography

We describe experimental investigations of the structure of two-dimensional spherical crystals. The crystals, formed by beads self-assembled on water droplets in oil, serve as model systems for exploring very general theories about the minimum energy configurations of particles with arbitrary repulsive interactions on curved surfaces. Above a critical system size we find that crystals develop distinctive high-angle grain boundaries, or scars, not found in planar crystals. The number of excess defects in a scar is shown to grow linearly with the dimensionless system size. The observed slope is expected to be universal, independent of the microscopic potential.Comment: 4 pages, 3 eps figs (high quality images available from Mark Bowick

Influence of two different resection techniques (conventional liver resection versus anterior approach) of liver metastases from colorectal cancer on hematogenous tumor cell dissemination – prospective randomized multicenter trial

<p>Abstract</p> <p>Background</p> <p>Surgical hepatic resection remains the treatment of choice for patients with liver metastases from colorectal cancer despite the use of alternative therapeutic strategies. Although this procedure provides long-term survival in a significant number of patients, 50–75% of the patients develop intra- and/or extrahepatic recurrence. One possible reason for tumor recurrence may be intraoperative hematogenous tumor cell dissemination due to mechanical manipulation of the tumor during hepatic resection. Surgical technique may have an influence on hematogenous tumor cell spread. We hypothesize that hematogenous tumor cell dissemination may be reduced by using the anterior approach technique compared to conventional liver resection.</p> <p>Methods/Design</p> <p>This is a multi-centre prospective randomized controlled, superiority trial to compare two liver resection techniques of liver metastases from colorectal cancer. 150 patients will be included and randomized intraoperatively after surgical exploration just prior to resection. The primary objective is to compare the anterior approach with the conventional liver resection technique with regard to intraoperative haematogenous tumor cell dissemination. As secondary objectives we examine five year survival rates (OS and DFS), blood loss, duration of operation, requirement of blood transfusions, morbidity rate, prognostic relevance of tumor cell detection in blood and bone marrow and the comparison of tumor cell detection by different detection methods.</p> <p>Conclusion</p> <p>This trial will answer the question whether there is an advantage for the anterior approach technique compared to the conventional resection group with regard to tumor cell dissemination. It will also add further information about prognostic differences, safety, advantages and disadvantages of each technique.</p> <p>Trial registration</p> <p>Current controlled trials – <b>ISRCTN45066244</b></p

Incompressible strips in dissipative Hall bars as origin of quantized Hall plateaus

We study the current and charge distribution in a two dimensional electron system, under the conditions of the integer quantized Hall effect, on the basis of a quasi-local transport model, that includes non-linear screening effects on the conductivity via the self-consistently calculated density profile. The existence of ``incompressible strips'' with integer Landau level filling factor is investigated within a Hartree-type approximation, and non-local effects on the conductivity along those strips are simulated by a suitable averaging procedure. This allows us to calculate the Hall and the longitudinal resistance as continuous functions of the magnetic field B, with plateaus of finite widths and the well-known, exactly quantized values. We emphasize the close relation between these plateaus and the existence of incompressible strips, and we show that for B values within these plateaus the potential variation across the Hall bar is very different from that for B values between adjacent plateaus, in agreement with recent experiments.Comment: 13 pages, 11 figures, All color onlin