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

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

Recent Advances on the Analysis of Polychrome Works of Art: SERS of Synthetic Colorants and Their Mixtures With Natural Dyes

The development and application of proper sample pretreatments is often a key step toward the successful analysis of dyes used as artists' materials by surface-enhanced Raman spectroscopy (SERS). Complexation of the organic colorants with metal ions to dye fabrics and produce lake pigments, as well as undesired interactions with other matrix components such as substrate, binding media, fillers, and extenders, are just some of the issues that typically complicate dye identification in minute samples from invaluable artworks and museum objects. These concerns may be addressed by using, prior to SERS analysis, ad-hoc sample pretreatments that, in addition to increasing the technique's sensitivity, favorably affect its selectivity toward certain molecules or molecular classes. The present work describes a newly developed sample pretreatment based on the use of nitric acid that has proven crucial for the successful detection of aniline and xanthene dyes–the first synthetic organic colorants to be used in printing and painting, among other art forms–in microscopic samples from works of art such as a 19th-century silk fabric, paper cut-outs by Henri Matisse, Vincent Van Gogh's Irises, and Japanese woodblock prints. This treatment promotes the hydrolysis of the dye-metal bond in mordant dyes or lake pigments, resulting in a more efficient adsorption of the dye molecules on the SERS-active substrate and, hence, enabling the acquisition of high-quality spectra. In the case of synthetic colorants, this method shows advantages over hydrolysis with hydrofluoric acid–a procedure previously established for the analysis of red lakes prepared from natural dyes. The nitric acid treatment presented here may be integrated into a multi-step methodology that, by exploiting differences in solubility of various dyes and lake pigments, has enabled for the first time to successfully characterize intentional mixtures of natural and synthetic colorants of the xanthene and anthraquinone molecular classes, i.e., eosin Y and carmine, in a selection of Japanese prints of the Meiji era. The present study paves the way for the systematic identification of synthetic dyes in objects of artistic and archeological interest, even when they are present in mixtures with natural organic colorants

Bayesian inferences of the thermal properties of a wall using temperature and heat flux measurements

The assessment of the thermal properties of walls is essential for accurate building energy simulations that are needed to make effective energy-saving policies. These properties are usually investigated through in-situ measurements of temperature and heat flux over extended time periods. The one-dimensional heat equation with unknown Dirichlet boundary conditions is used to model the heat transfer process through the wall. In [F. Ruggeri, Z. Sawlan, M. Scavino, R. Tempone, A hierarchical Bayesian setting for an inverse problem in linear parabolic PDEs with noisy boundary conditions, Bayesian Analysis 12 (2)(2017) 407-433], it was assessed the uncertainty about the thermal diffusivity parameter using different synthetic data sets. In this work, we adapt this methodology to an experimental study conducted in an environmental chamber, with measurements recorded every minute from temperature probes and heat flux sensors placed on both sides of a solid brick wall over a five-day period. The observed time series are locally averaged, according to a smoothing procedure determined by the solution of a criterion function optimization problem, to fit the required set of noise model assumptions. Therefore, after preprocessing, we can reasonably assume that the temperature and the heat flux measurements have stationary Gaussian noise and we can avoid working with full covariance matrices. The results show that our technique reduces the bias error of the estimated parameters when compared to other approaches. Finally, we compute the information gain under two experimental setups to recommend how the user can efficiently determine the duration of the measurement campaign and the range of the external temperature oscillation

A timeline for the introduction of synthetic dyestuffs in Japan during the late Edo and Meiji periods

Abstract A widespread belief among scholars and connoisseurs of the Japanese color woodblock print (nishiki-e) holds that synthetic dyes were imported from the West in the 1860s, and soon came to be used for all nishiki-e colorants during the Meiji period. These “cheap imported aniline dyes” are widely described as “gaudy”, “garish”, and “strident”, and thought to stand in sharp contrast to more muted “natural” colorants that preceded them. This study calls this narrative into question through an analysis of the colorants of nishiki-e from 1860 until 1900, using surface-enhanced Raman spectroscopy coupled with micro-Raman, XRF and fiber optic reflectance spectroscopies. The results show that the introduction of synthetic dyes was gradual and selective, and that most of the customary colorants of the late Edo period continued in use. The results revealed a series of key turning points after 1860: (1) In 1864, the purple dye rosaniline became the first synthetic dye to be used in nishiki-e, at first in combination with Prussian blue for a more bluish color. From 1875, it was usually mixed or replaced with methyl violet for a stronger purple. (2) In early 1869, a dramatic and until recently unrecognized transition took place, from the longstanding use of safflower as the dominant red, to its total replacement by imported cochineal carmine. Carmine remained the primary red for the next two decades, often combined with vermillion. (3) In 1877, eosine appeared as the first synthetic red dye in nishiki-e, used alone for pink, and in mixture with carmine for red. (4) Finally, from 1889, a succession of red naphthol dyes of more striking color appeared. Just about this time, however, a tendency to more restrained use of color and more painterly effects began to emerge in nishiki-e, and with the exception of a burst of dynamic color in prints depicting the Sino–Japanese War (1894–95), the uses of strong colors in Meiji prints receded. A final key finding is that colorants were often combined, either through mixture in a bowl or on the printing block, or by two-step overprinting

MOESM1 of A timeline for the introduction of synthetic dyestuffs in Japan during the late Edo and Meiji periods

Additional file 1: Table S1. Table indicating: date of production, artist and title of the Meiji prints collection analyzed in this study. The prints in italic are part of the Metropolitan Museum of Art collection. Table S2. Table indicating: XRF, Raman and SERS analysis of the pigment materials used in the Meiji prints collection considered in this study