Superposition of stable and periodic patterns

1998 ◽  
pp. 53-70
Author(s):  
Hans Meinhardt
Keyword(s):  
Periodic Patterns

Forced Periodic and Quasi-Periodic Patterns in Anisotropic Systems

1996 ◽  
Vol 6 (2) ◽  
pp. 305-328 ◽  
Author(s):  
Atsushi Ogawa ◽  
Walter Zimmermann ◽  
Kyozi Kawasaki ◽  
Toshihiro Kawakatsu
Keyword(s):  
Periodic Patterns ◽  
Anisotropic Systems

High-Frequency Periodic Patterns Driven by Non-Radiative Fields Coupled with Marangoni Convection Instabilities on Laser-Excited Surfaces

2019 ◽  
Author(s):  
Anton Rudenko ◽  
Anthony Abou-Saleh ◽  
Florent Pigeon ◽  
Cyril Mauclair ◽  
Florence Garrelie, Prof. ◽  
...  
Keyword(s):  
High Frequency ◽  
Marangoni Convection ◽  
Periodic Patterns

scholarly journals Short-Pulse Lasers: A Versatile Tool in Creating Novel Nano-/Micro-Structures and Compositional Analysis for Healthcare and Wellbeing Challenges

Nanomaterials ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 712
Author(s):  
Ahmed Al-Kattan ◽  
David Grojo ◽  
Christophe Drouet ◽  
Alexandros Mouskeftaras ◽  
Philippe Delaporte ◽  
...  
Keyword(s):  
Laser Ablation ◽  
Surface Engineering ◽  
Short Pulse ◽  
Chemical Properties ◽  
Compositional Analysis ◽  
Periodic Patterns ◽  
Laser Ablation In Liquid ◽  
Micro Scale ◽  
Direct Laser ◽  
Contact Free

Driven by flexibility, precision, repeatability and eco-friendliness, laser-based technologies have attracted great interest to engineer or to analyze materials in various fields including energy, environment, biology and medicine. A major advantage of laser processing relies on the ability to directly structure matter at different scales and to prepare novel materials with unique physical and chemical properties. It is also a contact-free approach that makes it possible to work in inert or reactive liquid or gaseous environment. This leads today to a unique opportunity for designing, fabricating and even analyzing novel complex bio-systems. To illustrate this potential, in this paper, we gather our recent research on four types of laser-based methods relevant for nano-/micro-scale applications. First, we present and discuss pulsed laser ablation in liquid, exploited today for synthetizing ultraclean “bare” nanoparticles attractive for medicine and tissue engineering applications. Second, we discuss robust methods for rapid surface and bulk machining (subtractive manufacturing) at different scales by laser ablation. Among them, the microsphere-assisted laser surface engineering is detailed for its appropriateness to design structured substrates with hierarchically periodic patterns at nano-/micro-scale without chemical treatments. Third, we address the laser-induced forward transfer, a technology based on direct laser printing, to transfer and assemble a multitude of materials (additive structuring), including biological moiety without alteration of functionality. Finally, the fourth method is about chemical analysis: we present the potential of laser-induced breakdown spectroscopy, providing a unique tool for contact-free and space-resolved elemental analysis of organic materials. Overall, we present and discuss the prospect and complementarity of emerging reliable laser technologies, to address challenges in materials’ preparation relevant for the development of innovative multi-scale and multi-material platforms for bio-applications.

scholarly journals Does laser surface texturing really have a negative impact on the fatigue lifetime of mechanical components?

Friction ◽  
2021 ◽  
Author(s):  
Chia-Jui Hsu ◽  
Andreas Stratmann ◽  
Simon Medina ◽  
Georg Jacobs ◽  
Frank Mücklich ◽  
...  
Keyword(s):  
Boundary Lubrication ◽  
Surface Texturing ◽  
Contact Stresses ◽  
Laser Surface ◽  
Laser Surface Texturing ◽  
Wear Loss ◽  
Textured Surface ◽  
Periodic Patterns ◽  
Rolling Bearings ◽  
Fatigue Lifetime

AbstractLaser surface texturing (LST) has been proven to improve the tribological performance of machine elements. The micro-scale patterns manufactured by LST may act as lubricant reservoirs, thus supplying oil when encountering insufficient lubrication. However, not many studies have investigated the use of LST in the boundary lubrication regime, likely due to concerns of higher contact stresses that can occur with the increasing surface roughness. This study aims to examine the influence of LST on the fatigue lifetime of thrust rolling bearings under boundary lubrication. A series of periodic patterns were produced on the thrust rolling bearings, using two geometrically different designs, namely cross and dimple patterns. Base oil ISO VG 100 mixed with 0.05 wt% P of zinc dialkyldithiophosphate (ZDDP) was supplied. The bearings with cross patterns reduce the wear loss by two orders of magnitude. The patterns not only retain lubricant in the textured pockets but also enhance the formation of an anti-wear tribofilm. The tribofilm generation may be improved by the higher contact stresses that occur when using the textured surface. Therefore, in contrast to the negative concerns, the ball bearings with cross patterns were instead found to increase the fatigue life by a factor of three.

scholarly journals Direct Laser Interference Patterning of Diffraction Gratings in Safrofilcon-A Hydrogel: Fabrication and Hydration Assessment

Polymers ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 679
Author(s):  
Daniel Sola ◽  
Stephan Milles ◽  
Andrés F. Lasagni
Keyword(s):  
Laser Fluence ◽  
Contact Lenses ◽  
Laser Source ◽  
Spatial Period ◽  
Laser Interference ◽  
Periodic Patterns ◽  
Hydration Properties ◽  
Water Contact ◽  
Direct Laser ◽  
Direct Laser Interference Patterning

Refractive index modification by laser micro-structuration of diffractive optical devices in ophthalmic polymers has recently been applied for refractive correction in the fields of optics and ophthalmology. In this work, Safrofilcon-A hydrogel, used as soft contact lenses, was processed by direct laser interference patterning (DLIP) to fabricate linear periodic patterns on the surface of the samples. Periodic modulation of the surface was attained under two-beam interference by using a Q-switched laser source with emission at 263 nm and 4 ns pulse duration. Features of processed areas were studied as a function of both the interference spatial period and the laser fluence. Optical confocal microscopy used to evaluate the topography of the processed samples showed that both structured height and surface roughness increased with laser fluence. Static water contact angle (WCA) measurements were carried out with deionized water droplets on the structured areas to evaluate the hydration properties of DLIP structures. It was observed that the laser structured areas induced a delay in the hydration process. Finally, microstructural changes induced in the structured areas were assessed by confocal micro-Raman spectroscopy showing that at low laser fluences the polymer structure remained almost unaltered. In addition, Raman spectra of hydrated samples recovered the original shape of areas structured at low laser fluence.

scholarly journals Reducing the Bias of the Smoothed Log Periodogram Regression for Financial High-Frequency Data

Econometrics ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 40
Author(s):  
Erhard Reschenhofer ◽  
Manveer K. Mangat
Keyword(s):  
Simulation Study ◽  
High Frequency ◽  
Mean Squared Error ◽  
Estimation Methods ◽  
High Frequency Data ◽  
Frequency Data ◽  
Periodic Patterns ◽  
Typical Sample ◽  
Squared Error ◽  
Proper Interpretation

For typical sample sizes occurring in economic and financial applications, the squared bias of estimators for the memory parameter is small relative to the variance. Smoothing is therefore a suitable way to improve the performance in terms of the mean squared error. However, in an analysis of financial high-frequency data, where the estimates are obtained separately for each day and then combined by averaging, the variance decreases with the sample size but the bias remains fixed. This paper proposes a method of smoothing that does not entail an increase in the bias. This method is based on the simultaneous examination of different partitions of the data. An extensive simulation study is carried out to compare it with conventional estimation methods. In this study, the new method outperforms its unsmoothed competitors with respect to the variance and its smoothed competitors with respect to the bias. Using the results of the simulation study for the proper interpretation of the empirical results obtained from a financial high-frequency dataset, we conclude that significant long-range dependencies are present only in the intraday volatility but not in the intraday returns. Finally, the robustness of these findings against daily and weekly periodic patterns is established.

Visual Exploration and Analysis of Historic Hotel Visits

2007 ◽  
Vol 6 (1) ◽  
pp. 89-103 ◽  
Author(s):  
Chris Weaver ◽  
David Fyfe ◽  
Anthony Robinson ◽  
Deryck Holdsworth ◽  
Donna Peuquet ◽  
...  
Keyword(s):  
Data Collection ◽  
Essential Feature ◽  
Group Behavior ◽  
Visual Exploration ◽  
Intelligence Analysis ◽  
Periodic Patterns ◽  
Analysis And Evaluation ◽  
Central Pennsylvania ◽  
Additional Data Collection ◽  
Spatial And Temporal Characteristics

Understanding the spatial and temporal characteristics of individual and group behavior in social networks is a critical component of visual tools for intelligence analysis, emergency management, consumer analysis, and human geography. Identification and analysis of patterns of recurring events is an essential feature of such tools. In this paper, we describe an interactive visual tool for exploring the visitation patterns of guests at two hotels in central Pennsylvania from 1894 to 1900. The centerpiece of the tool is a wrapping spreadsheet technique, called reruns, that reveals regular and irregular periodic patterns of events in multiple overlapping artificial and natural calendars. Implemented as a coordinated multiple view visualization in Improvise, the tool is in ongoing development through an iterative process of data collection, transcription, hypothesis, design, discovery, analysis, and evaluation in close collaboration with historical geographers. Numerous discoveries have driven additional data collection from archival newspaper and census sources, as well as plans to enhance analysis of spatial patterns using historic weather records and railroad schedules. Distributed online evaluations of usability and usefulness have resulted in feature and design recommendations that are being incorporated into the tool.

Discovering periodic patterns of nodal encounters in mobile networks

2013 ◽  
Vol 9 (6) ◽  
pp. 892-912 ◽  
Author(s):  
Zhiyu Wang ◽  
Mario A. Nascimento ◽  
Mike H. MacGregor
Keyword(s):  
Mobile Networks ◽  
Periodic Patterns
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