Hysteresis from dynamically pinned sliding states

We report a surprising hysteretic behavior in the dynamics of a simple one-dimensional nonlinear model inspired by the tribological problem of two sliding surfaces with a thin solid lubricant layer in between. In particular, we consider the frictional dynamics of a harmonic chain confined between two rigid incommensurate substrates which slide with a fixed relative velocity. This system was previously found, by explicit solution of the equations of motion, to possess plateaus in parameter space exhibiting a remarkable quantization of the chain center-of-mass velocity (dynamic pinning) solely determined by the interface incommensurability. Starting now from this quantized sliding state, in the underdamped regime of motion and in analogy to what ordinarily happens for static friction, the dynamics exhibits a large hysteresis under the action of an additional external driving force F_ext. A critical threshold value F_c of the adiabatically applied force F_ext is required in order to alter the robust dynamics of the plateau attractor. When the applied force is decreased and removed, the system can jump to intermediate sliding regimes (a sort of ``dynamic'' stick-slip motion) and eventually returns to the quantized sliding state at a much lower value of F_ext. On the contrary no hysteretic behavior is observed as a function of the external driving velocity.Comment: 12 pages, 5 figures, ECOSS 200

Solitons and exact velocity quantization of incommensurate sliders

We analyze in some detail the recently discovered velocity quantization phenomena in the classical motion of an idealized one-dimensional solid lubricant, consisting of a harmonic chain interposed between two periodic sliders. The ratio w = v_cm/v_ext of the chain center-of-mass velocity to the externally imposed relative velocity of the sliders is pinned to exact ``plateau'' values for wide ranges of parameters, such as sliders corrugation amplitudes, external velocity, chain stiffness and dissipation, and is strictly determined by the commensurability ratios alone. The phenomenon is caused by one slider rigidly dragging the density solitons (kinks/antikinks) that the chain forms with the other slider. Possible consequences of these results for some real systems are discussed.Comment: 12 pages 6 figures. Small fixup after Referee's comments. In print in J. Phys.: Condens. Matte

Exploring the role of fallopian ciliated cells in the pathogenesis of high-grade serous ovarian cancer

High-grade serous epithelial ovarian cancer (HGSOC) is the fifth leading cause of cancer death in women and the first among gynecological malignancies. Despite an initial response to standard chemotherapy, most HGSOC patients relapse. To improve treatment options, we must continue investigating tumor biology. Tumor characteristics (e.g., risk factors and epidemiology) are valuable clues to accomplish this task. The two most frequent risk factors for HGSOC are the lifetime number of ovulations, which is associated with increased oxidative stress in the pelvic area caused by ovulation fluid, and a positive family history due to genetic factors. In the attempt to identify novel genetic factors (i.e., genes) associated with HGSOC, we observed that several genes in linkage with HGSOC are expressed in the ciliated cells of the fallopian tube. This finding made us hypothesize that ciliated cells, despite not being the cell of origin for HGSOC, may take part in HGSOC tumor initiation. Specifically, malfunction of the ciliary beat impairs the laminar fluid flow above the fallopian tube epithelia, thus likely reducing the clearance of oxidative stress caused by follicular fluid. Herein, we review the up-to-date findings dealing with HGSOC predisposition with the hypothesis that fallopian ciliated cells take part in HGSOC onset. Finally, we review the up-to-date literature concerning genes that are located in genomic loci associated with epithelial ovarian cancer (EOC) predisposition that are expressed by the fallopian ciliated cells

Criptografía en el profesorado de matemática

La actividad descripta en este artículo es consecuencia de la preocupación de los autores por hacer conocer a los estudiantes de los profesorados de matemática la importancia de la matemática en el desarrollo de otras disciplinas científicas y de la tecnología. De hecho, con esta actividad se logró incluir el tratamiento del protocolo criptográfico RSA (un tema de relevancia en la comunicación digital) en un curso de álgebra del profesorado de matemática de la Universidad Nacional de Gral. Sarmiento. Este artículo se concentra en describir el tratamiento dado al tema para su puesta en práctica efectiva en el aula. Con el objetivo de favorecer en los estudiantes el desarrollo de habilidades de lecto-escritura, se interactuó con un docente de ese área. Este docente acompañó a los docentes de matemática participando del diseñó, dictado de clases, producción de materiales específicos y de la evaluación. Entendemos que este tipo de trabajo es novedoso en las aulas de matemática. La apreciación de los docentes es que la actividad descripta promovió en los estudiantes el desarrollo de habilidades de resolución de problemas, de escritura académica y favoreció aprendizajes propios de los contenidos de álgebra

Kink plateau dynamics in finite-size lubricant chains

We extend the study of velocity quantization phenomena recently found in the classical motion of an idealized 1D model solid lubricant -- consisting of a harmonic chain interposed between two periodic sliding potentials [Phys. Rev. Lett. 97, 056101 (2006)]. This quantization is due to one slider rigidly dragging the commensurate lattice of kinks that the chain forms with the other slider. In this follow-up work we consider finite-size chains rather than infinite chains. The finite size (i) permits the development of robust velocity plateaus as a function of the lubricant stiffness, and (ii) allows an overall chain-length re-adjustment which spontaneously promotes single-particle periodic oscillations. These periodic oscillations replace the quasi-periodic motion produced by general incommensurate periods of the sliders and the lubricant in the infinite-size model. Possible consequences of these results for some real systems are discussed.Comment: 12 pages, 5 figures, ECOSS 200

Beyond ‘geo-economics’: advanced unevenness and the anatomy of German austerity

This article aims to shed new light on Germany’s domineering role in the eurocrisis. I argue that the realist-inspired depiction of Germany as a ‘geo-economic power’, locked into zero-sum competition with its European partners, is built around an empty core: unable to theorise how anarchy shapes the calculus of states where security competition has receded, it cannot explain why German state managers have insisted on an austerity response to the crisis despite its significant risks and costs even for Germany itself. To unlock this puzzle, this article outlines a version of uneven and combined development (UCD) that is better able to capture the international pressures and opportunities faced by policy elites in advanced capitalist states that no longer encounter one another as direct security rivals. Applied to Germany, this lens reveals a twofold unevenness in the historical structures and growth cycles of capitalist economies that shape its contradictory choice for austerity. In the long run, the reorientation of the export-dependent German economy from Europe towards Asian and Latin American late industrialisers renders the structural adjustment of the eurozone an opportunity—from the cost-saving view of German manufacturers producing in the European home market for export abroad, as well as for German state officials keen to sustain a crumbling class compromise centred on Germany’s world market success. In the short term, however, its exposed position between the divergent post-crisis trajectories of the US and Europe accelerates pressures for austerity beyond what German state and corporate elites would otherwise consider feasible