Protocol-independent granular temperature supported by numerical simulations.

A possible approach to the statistical description of granular assemblies starts from Edwards's assumption that all blocked states occupying the same volume are equally probable [Edwards and Oakeshott, Physica A 157, 1080 (1989)]. We performed computer simulations using two-dimensional polygonal particles excited periodically according to two different protocols: excitation by pulses of "negative gravity" and excitation by "rotating gravity." The first protocol exhibits a nonmonotonous dependency of the mean volume fraction on the pulse strength. The overlapping histogram method is used in order to test whether the volume distribution is described by a Boltzmann-like distribution and to calculate the inverse compactivity as well as the logarithm of the partition sum. We find that the mean volume is a unique function of the measured granular temperature, independently of the protocol and of the branch in ϕ(g), and that all determined quantities are in agreement with Edwards's theory.

A master curve for the onset of shear induced restructuring of fractal colloidal aggregates.

Colloidal aggregates exposed to shear flow exhibit a size-dependent qualitative behavior [Becker et al. JCIS, 339, 362-372, 2009]. Under the same flow conditions small aggregates rotate like rigid bodies, whereas larger aggregates change their structure and even bigger aggregates break. In this study the transition from the rotational regime to the restructuring regime is investigated by DEM simulations. We applied a model for tangential interaction, capable of supporting bond-bending moments and torsional torques [Becker, Briesen, Phys. Rev. E, 78, 2008, 061404]. The probability for an aggregate to be affected by restructuring changes with the number of primary particle from zero to one in a small interval. The probability becomes a master curve being independent of the shear flow and the interparticle interactions if it is represented as a function of the relative deviation from the critical particles number, i.e. the number of primary particle where the probability of restructuring is equal to 0.5. Investigating the dependency of the critical particle number on the shear rates reveals power law relations which adequately represents the data. The exponents in the power law relations can particularly obtained from a fractal scaling argument.

Restructuring of colloidal aggregates in shear flows and limitations of the free-draining approximation.

We investigated the restructuring behavior of colloidal aggregates by means of the discrete element method. We used a recently proposed model [V. Becker, H. Briesen, Physical Review E 78 (6) (2008) 061404] for tangential inter-particle forces, capable of supporting bending moments. We extended this model by the capability of supporting torsional moments. The time evolution of the aggregates' radius of gyration was tracked and a power law relation between the number of primary particles and the final radius of gyration was found. For the hydrodynamic drag forces the free-draining approximation is employed. We investigated the quality of the free-draining approximation by fully resolved finite element simulations for small aggregates. We found that the free-draining approximation overestimates the drag forces and we identified the usage of effective shear rates as a possible ansatz for reduced modeling of hydrodynamic forces.

Coefficient of tangential restitution for the linear dashpot model.

The linear dashpot model for the inelastic normal force between colliding spheres leads to a constant coefficient of normal restitution, epsilonn=const, which makes this model very popular for the investigation of dilute and moderately dense granular systems. For two frequently used models for the tangential interaction force we determine the coefficient of tangential restitution, epsilont, both analytically and by numerical integration of Newton's equation. Although epsilonn=const for the linear-dashpot model, we obtain pronounced and characteristic dependences of the tangential coefficient on the impact velocity, epsilont=epsilont(g). The results may be used for event-driven simulations of granular systems of frictional particles.

Tangential-force model for interactions between bonded colloidal particles.

Recently, Pantina and Furst [Phys. Rev. Lett. 94, 138301 (2005)] experimentally demonstrated the existence of tangential forces between bonded colloidal particles and the capability of these bonds to supporting bending moments. We introduce a model to be used in computer simulations that describes these tangential interactions. We show how the model parameters can be determined from experimental data. Simulations using the model are in agreement to the measurement by Pantina and Furst. Application of the model to an aggregate with fractal structure leads to more realistic behavior than using classical approaches only.

Role of interactions in ferrofluid thermal ratchets.

Orientational fluctuations of colloidal particles with magnetic moments may be rectified with the help of external magnetic fields with suitably chosen time dependence. As a result a noise-driven rotation of particles occurs giving rise to a macroscopic torque per volume of the carrier liquid. We investigate the influence of mutual interactions between the particles on this ratchet effect by studying a model system with mean-field interactions. The stochastic dynamics may be described by a nonlinear Fokker-Planck equation for the collective orientation of the particles which we solve approximately by using the effective field method. We determine an interval for the ratio between coupling strength and noise intensity for which a self-sustained rectification of fluctuations becomes possible. The ratchet effect then operates under conditions for which it was impossible in the absence of interactions.

[Rokitansky and Virchow: throes about the scientific term of disease]. / Rokitansky und Virchow: Geburtswehen um den naturwissenschaftlichen Krankheitsbegriff.

The scientific conception of disease became established in the 19th century and resulted in medicine becoming a branch of the natural sciences. In Vienna, the development of pathoanatomy is closely linked with the work of Carl Rokitansky, who used the postmortem examination to draw conclusions that would guide the physician in making future clinical diagnoses. It were Rokitansky and Skoda who developed the II. Viennese School, the "young Viennese School". The founder of the new school of medicine was thus a pathoanatomist. In 1846, Rokitansky published the first volume of his "Compendium of General Pathological Anatomy". In Berlin, there was at the time a particularly avid group of young physicians who had learned to "think cellularly". Rudolf Virchow, a member of the group, was asked to review the newly published volume of Rokitansky's compendium. The 25-year-old was particularly scathing in his criticism, determined to prevent a new dyscrasia theory right from the very beginning. For the next edition of his work, Rokitansky rewrote the "compendium" completely, now in natural scientific terms, and in doing so, encouraged Virchow to further develop the natural scientific conception of disease. Rokitansky's factual approval thus gave Virchow valuable support on his way to cellular pathology.

Expression of cadherin-8 in renal cell carcinoma and fetal kidney.

Cadherins represent a family of calcium-dependent cell adhesion molecules with an important regulatory function for maintenance of tissue architecture. Alterations of cadherin expression have been demonstrated in the development and progression of different epithelial tumors. In renal cell carcinoma (RCC), the majority of tumors express N-cadherin and cadherin-6. Screening a series of 16 RCC cell lines for the expression of different novel type II cadherins by RT-PCR revealed a complex pattern of cadherin expression: cadherins 6 and 14 were expressed in most of the RCC cell lines, whereas cadherins 11, 12 and 13 could not be detected at all. Interestingly, cadherin-8, previously shown in mice to be restricted to the CNS and thymus during development, was detected by RT-PCR, immunofluorescence and in situ hybridization in 4 of 16 RCC cell lines as well as in paraffin sections of the corresponding human RCC biopsies. In normal renal tissue, however, cadherin-8 could be detected only during the early stages of kidney development. These results suggest that alterations of type II cadherin expression may play a role in RCC development. In particular, cadherin-8 may be involved in both kidney morphogenesis as well as tumorigenesis in some types of RCC.

Human alpha-defensins HNPs-1, -2, and -3 in renal cell carcinoma: influences on tumor cell proliferation.

The alpha-defensins human neutrophil peptides (HNPs)-1, -2, and -3 have been described as cytotoxic peptides with restricted expression in neutrophils and in some lymphocytes. In this study we report that HNPs-1, -2, and -3 are also expressed in renal cell carcinomas (RCCs). Several RCC lines were found to express mRNA as well as the specific peptides of HNP-1, -2, and -3 demonstrated by reverse transcriptase-polymerase chain reaction, mass spectrometric, and flow cytometric analyses. At physiological concentrations HNPs-1, -2, and -3 stimulated cell proliferation of selected RCC lines in vitro but at high concentrations were cytotoxic for all RCC lines tested. As in RCC lines, alpha-defensins were also detected in vivo in malignant epithelial cells of 31 RCC tissues in addition to their expected presence in neutrophils. In most RCC cases randomly, patchy immunostaining of alpha-defensins on epithelial cells surrounding neutrophils was seen, but in six tumors of higher grade malignancy all tumor cells were diffusely stained. Cellular necrosis observed in RCC tissues in association with extensive patches of HNP-1, -2, and -3, seemed to be related to high concentrations of alpha-defensins. The in vitro and in vivo findings suggest that alpha-defensins are frequent peptide constituents of malignant epithelial cells in RCC with a possible direct influence on tumor proliferation.