Journal articles: 'Processi periodici'

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Ciglioni, Laura. "L'Italia del miracolo economico e la stampa statunitense." MONDO CONTEMPORANEO, no. 3 (March 2013): 81–128. http://dx.doi.org/10.3280/mon2012-003003.

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Il saggio ricostruisce l'atteggiamento, le analisi e i giudizi della stampa statunitense di fronte al miracolo economico italiano tra il 1960 e il 1964. Il contributo offre due diversi piani di lettura, fra loro complementari. Da un lato, propone una ricostruzione delle dinamiche del miracolo economico (i fattori della crescita, i settori trainanti, le radici della crisi), filtrate attraverso lo sguardo degli osservatori statunitensi, con l'intento di comprendere quali luci e ombre la stagione del boom contribuě a proiettare sull'immagine complessiva dell'Italia allora diffusa oltreoceano. Dall'altro, intende contribuire a un'analisi dell'opinione pubblica americana negli anni Sessanta, facendone emergere in controluce orientamenti e percezioni, convinzioni e prioritŕ, pregiudizi e paure, anzitutto rispetto al problema della crescita economica e dei modelli di sviluppo nel contesto della Guerra Fredda, ma anche in relazione ad alcune scelte dell'amministrazione Kennedy verso l'alleato europeo e ai processi di modernizzazione in corso nella penisola. La ricerca č basata, oltre che su documentazione del Dipartimento di Stato americano, su quotidiani e periodici statunitensi selezionati in base a diffusione, autorevolezza, orientamento e pubblico di riferimento.

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Cipra, Tomáš. "Periodic moving average process." Applications of Mathematics 30, no. 3 (1985): 218–29. http://dx.doi.org/10.21136/am.1985.104142.

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Anděl, Jiří, and Asunción Rubio. "On interpolation in periodic autoregressive processes." Applications of Mathematics 31, no. 6 (1986): 480–85. http://dx.doi.org/10.21136/am.1986.104225.

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Shpak, Olexandr. "Speeded search of the periodic processes of dynamical systems." Odes’kyi Politechnichnyi Universytet. Pratsi, no. 1 (April 27, 2016): 80–90. http://dx.doi.org/10.15276/opu.1.48.2016.10.

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Durrande, Nicolas, James Hensman, Magnus Rattray, and Neil D. Lawrence. "Detecting periodicities with Gaussian processes." PeerJ Computer Science 2 (April 13, 2016): e50. http://dx.doi.org/10.7717/peerj-cs.50.

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We consider the problem of detecting and quantifying the periodic component of a function given noise-corrupted observations of a limited number of input/output tuples. Our approach is based on Gaussian process regression, which provides a flexible non-parametric framework for modelling periodic data. We introduce a novel decomposition of the covariance function as the sum of periodic and aperiodic kernels. This decomposition allows for the creation of sub-models which capture the periodic nature of the signal and its complement. To quantify the periodicity of the signal, we derive a periodicity ratio which reflects the uncertainty in the fitted sub-models. Although the method can be applied to many kernels, we give a special emphasis to the Matérn family, from the expression of the reproducing kernel Hilbert space inner product to the implementation of the associated periodic kernels in a Gaussian process toolkit. The proposed method is illustrated by considering the detection of periodically expressed genes in thearabidopsisgenome.

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Fan, Chunlei, and Qun Ding. "Effects of Limited Computational Precision on the Discrete Chaotic Sequences and the Design of Related Solutions." Complexity 2019 (January 1, 2019): 1–10. http://dx.doi.org/10.1155/2019/3510985.

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In this paper, we analyzed the periodicity of discrete Logistic and Tent sequences with different computational precision in detail. Further, we found that the process of iterations of the Logistic and Tent mapping is composed of transient and periodic stages. Surprisingly, for the different initial iterative values, we first discovered that all periodic stages have the same periodic limit cycles. This phenomenon has seriously affected the security of chaotic cipher. To solve this problem, we designed a novel discrete chaotic sequence generator based on m-sequence and discrete chaotic mapping. The experimental results indicated that the chaotic sequence generator can generate pseudorandom chaotic sequences with large periodicity and good performance under the condition of limited computational precision.

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Rodkina, Alexandra, Nikolai Dokuchaev, and John Appleby. "On limit periodicity of discrete time stochastic processes." Stochastics and Dynamics 14, no. 04 (September 22, 2014): 1450011. http://dx.doi.org/10.1142/s0219493714500117.

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We consider a discrete time dynamic system described by a difference equation with periodic coefficients and with additive stochastic noise. We investigate the possibility of the periodicity of the solution. In particular, we established sufficient conditions for convergence of the solution in mean square or almost surely to some stochastic periodic process.

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Long, John A., and Paul C. Stoy. "Quantifying the periodicity of Heinrich and Dansgaard–Oeschger events during Marine Oxygen Isotope Stage 3." Quaternary Research 79, no. 3 (May 2013): 413–23. http://dx.doi.org/10.1016/j.yqres.2013.02.003.

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AbstractData from multiple ice and sediment cores in the North Atlantic show that Marine Oxygen Isotope Stage 3 (MIS 3) was characterized by recurring millennial-scale variations in climate, but the periodic behavior of the well-known millennial-scale variations, Heinrich events and Dansgaard–Oeschger events, is uncertain. We use oxygen isotope values from the Greenland Ice Sheet Project 2 (GISP2) and North Greenland Ice Core Project (NGRIP) ice cores and estimated sea-surface temperature derived from a Bermuda Rise marine sediment core as climate proxies to assess the periodic behavior of Heinrich events and Dansgaard–Oeschger events using Lomb–Scargle spectral decomposition and continuous time autoregressive models. We find that continuous time autoregressive models produce less variable estimates of periodicity for Heinrich events than Lomb–Scargle methods. Heinrich events during MIS 3 are periodic with an estimated periodicity of 6.29–6.49 ka in the GISP 2 ice core, 6.71–6.76 ka in the marine sediment core, and 7.89–8.23 ka in the NGRIP core. There is insufficient evidence from these data to conclude that Dansgaard–Oeschger events exhibit a single periodicity during MIS 3. We also find that the periodic behavior of millennial-scale variations depends on the observational time frame.

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Herrera, R., and A. Gómez. "Multislice calculations for quasi-periodic and non-periodic objects." Proceedings, annual meeting, Electron Microscopy Society of America 48, no. 4 (August 1990): 138–39. http://dx.doi.org/10.1017/s0424820100173820.

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Computer simulations of electron diffraction patterns and images are an essential step in the process of structure and/or defect elucidation. So far most programs are designed to deal specifically with crystals, requiring frequently the space group as imput parameter. In such programs the deviations from perfect periodicity are dealt with by means of “periodic continuation”.However, for many applications involving amorphous materials, quasiperiodic materials or simply crystals with defects (including finite shape effects) it is convenient to have an algorithm capable of handling non-periodicity. Our program “HeGo” is an implementation of the well known multislice equations in which no periodicity assumption is made whatsoever. The salient features of our implementation are: 1) We made Gaussian fits to the atomic scattering factors for electrons covering the whole periodic table and the ranges [0-2]Å−1 and [2-6]Å−1.

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Giorno, Virginia, and Amelia G. Nobile. "Time-Inhomogeneous Feller-Type Diffusion Process in Population Dynamics." Mathematics 9, no. 16 (August 7, 2021): 1879. http://dx.doi.org/10.3390/math9161879.

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The time-inhomogeneous Feller-type diffusion process, having infinitesimal drift α(t)x+β(t) and infinitesimal variance 2r(t)x, with a zero-flux condition in the zero-state, is considered. This process is obtained as a continuous approximation of a birth-death process with immigration. The transition probability density function and the related conditional moments, with their asymptotic behaviors, are determined. Special attention is paid to the cases in which the intensity functions α(t), β(t), r(t) exhibit some kind of periodicity due to seasonal immigration, regular environmental cycles or random fluctuations. Various numerical computations are performed to illustrate the role played by the periodic functions.

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Yu, Xiangzhan, Zhaoxin Zhang, Haining Yu, Feng Jiang, and Wen Ji. "An Asynchronous Periodic Sequential Pattern Mining Algorithm with Multiple Minimum Item Supports for Ad Hoc Networking." Journal of Sensors 2015 (2015): 1–13. http://dx.doi.org/10.1155/2015/461659.

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The original sequential pattern mining model only considers occurrence frequencies of sequential patterns, disregarding their occurrence periodicity. We propose an asynchronous periodic sequential pattern mining model to discover the sequential patterns that not only occur frequently but also appear periodically. For this mining model, we propose a pattern-growth mining algorithm to mine asynchronous periodic sequential patterns with multiple minimum item supports. This algorithm employs a divide-and-conquer strategy to mine asynchronous periodic sequential patterns in a depth-first manner recursively. We describe the process of algorithm realization and demonstrate the efficiency and stability of the algorithm through experimental results.

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Sun, Qiwen, Feng Jiao, and Jianshe Yu. "The dynamics of gene transcription with a periodic synthesis rate." Nonlinear Dynamics 104, no. 4 (June 2021): 4477–92. http://dx.doi.org/10.1007/s11071-021-06569-y.

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AbstractThe periodic transcription output is ubiquitously observed in an isogenic cell population. To understand mechanisms of cyclic behavior in transcription, we extend the gene activation process in the two-state model by assuming that the synthesis rate is periodic. We derive the analytical forms of the mean transcript level and the noise. The limits of them indicate that the mean level and the noise display periodic behaviors. Numerical examples strongly suggest that the transcription system with a periodic synthesis rate generates more noise than that with a constant rate but maintains transcription homeostasis in each period. It is also suggested that if the periodicity is not considered, the calculated noise may be greater than the real value.

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Sarkar, Arkadipta, Pankaj Kushwaha, Alok C. Gupta, Varsha R. Chitnis, and Paul J. Wiita. "Multi-waveband quasi-periodic oscillations in the light curves of blazar CTA 102 during its 2016–2017 optical outburst." Astronomy & Astrophysics 642 (October 2020): A129. http://dx.doi.org/10.1051/0004-6361/202038052.

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Context. Quasi-periodic fluctuations in the light curves of blazars can provide insight into the underlying emission process. This type of flux modulation hints at periodic physical processes that result in emission. CTA 102, a flat spectrum radio quasar at a redshift of 1.032, has displayed significant activity since 2016. The multi-waveband light curve of CTA 102 shows signs of quasi-periodic oscillations during the 2016–2017 flare. Aims. Our goal is to rigorously quantify the presence of any possible periodicity in the emitted flux during the mentioned period and to explore the possible causes that can give rise to it. Methods. Techniques such as the Lomb-Scargle periodogram and weighted wavelet z-transform were employed to observe the power emitted at different frequencies. To quantify the significance of the dominant period, Monte-Carlo techniques were employed to consider an underlying smooth bending power-law model for the power spectrum. In addition, the light curve was modeled using an autoregressive process (AR1) to analytically obtain the significance of the dominant period. Lastly, the light curve was modeled using a generalized autoregressive integrated moving average (ARIMA) process to check whether introducing a seasonal (periodic) component results in a statistically preferable model. Results. Highly significant, simultaneous quasi-periodic oscillations (QPOs) were observed in the γ-ray and optical fluxes of blazar CTA 102 during its highest optical activity episode in 2016–2017. The periodic flux modulation had a dominant period of ∼7.6 days and lasted for ∼8 cycles (MJD 57710–57770). All of the methods used point toward significant (> 4σ) quasi-periodic modulation in both γ-ray and optical fluxes. Conclusions. Several possible models were explored while probing the origin of the periodicity, and by extension, the 2016–2017 optical flare. The best explanation for the detected QPO appears to be a region of enhanced emission (blob), moving helically inside the jet.

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ZHU, Z. K., ZHIYONG HE, ANZHU WANG, and SHIBIN WANG. "SYNCHRONOUS ENHANCEMENT OF PERIODIC TRANSIENTS ON POLAR DIAGRAM FOR MACHINE FAULT DIAGNOSIS." International Journal of Wavelets, Multiresolution and Information Processing 07, no. 04 (July 2009): 427–42. http://dx.doi.org/10.1142/s0219691309003008.

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A periodic transient detection and representation method, termed synchronous enhancement of periodic feature (SEPF), based on the Continuous Wavelet Transform (CWT) is proposed. This method first represents a given signal in the time-scale domain through CWT and then maps the resulted wavelet coefficients into the polar diagram using the given potential periods. Transient features would thus be synchronously enhanced at a certain area if the mapping time period matches that of the transient vibrations. The simulation study and the applications in the gearbox and bearing fault diagnosis verify the effectiveness of the proposed method in detecting the periodical transient vibrations.

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Seidel, Carsten, Daliborka Nikolić, Matthias Felischak, Menka Petkovska, Andreas Seidel-Morgenstern, and Achim Kienle. "Optimization of Methanol Synthesis under Forced Periodic Operation." Processes 9, no. 5 (May 15, 2021): 872. http://dx.doi.org/10.3390/pr9050872.

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Traditionally, methanol is produced in large amounts from synthesis gas with heterogeneous Cu/ZnO/Al2O3 catalysts under steady state conditions. In this paper, the potential of alternative forced periodic operation modes is studied using numerical optimization. The focus is a well-mixed isothermal reactor with two periodic inputs, namely, CO concentration in the feed and total feed flow rate. Exploiting a detailed kinetic model which also describes the dynamics of the catalyst, a sequential NLP optimization approach is applied to compare optimal steady state solutions with optimal periodic regimes. Periodic solutions are calculated using dynamic optimization with a periodicity constraint. The NLP optimization is embedded in a multi-objective optimization framework to optimize the process with respect to two objective functions and generate the corresponding Pareto fronts. The first objective is the methanol outlet flow rate. The second objective is the methanol yield based on the total carbon in the feed. Additional constraints arising from the complex methanol reaction and the practical limitations are introduced step by step. The results show that significant improvements for both objective functions are possible through periodic forcing of the two inputs considered here.

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WANG, SHIHONG, WEIRONG LIU, HUAPING LU, JINYU KUANG, and GANG HU. "PERIODICITY OF CHAOTIC TRAJECTORIES IN REALIZATIONS OF FINITE COMPUTER PRECISIONS AND ITS IMPLICATION IN CHAOS COMMUNICATIONS." International Journal of Modern Physics B 18, no. 17n19 (July 30, 2004): 2617–22. http://dx.doi.org/10.1142/s0217979204025798.

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Fundamental problems of periodicity and transient process to periodicity of chaotic trajectories in computer realization with finite computation precision is investigated by taking single and coupled Logistic maps as examples. Empirical power law relations of the period and transient iterations with the computation precisions and the sizes of coupled systems are obtained. For each computation we always find, by randomly choosing initial conditions, a single dominant periodic trajectory which is realized with major portion of probability. These understandings are useful for possible applications of chaos, e.g., chaotic cryptography in secure communication.

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Jiang, Zhongyuan, Huan Wang, Xiaoliang Chen, Mingwei Tang, and Jianhong Ye. "An Enhanced Supervisory Control Strategy for Periodicity Mutual Exclusions in Discrete Event Systems Based on Petri Nets." Discrete Dynamics in Nature and Society 2017 (2017): 1–14. http://dx.doi.org/10.1155/2017/1395142.

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Mutual exclusion problems widely exist in discrete event systems in which several processes will compete for the common resource for maintaining their normal running. This competition is mutually exclusive. However, a special behavior, that is, periodic mutual exclusion behavior, is important for many discrete event systems. Once a process obtains the common resource, it will consecutively obtain the common resource in the following several competitions. The other processes should wait for the release of the common resource. All processes will compete for the common resource again after the common resource is released. These competitions have obvious periodicity. In this paper, a methodology is proposed to design periodic mutual exclusion supervisors to control the periodic mutual exclusion behavior in discrete event systems. Moreover, two original structural conversion concepts, calledk-derivation andk-convergence processes, are proposed to construct the periodic mutual exclusion supervisors. The discussion results show that many undesirable execution sequences are forbidden since the periodic mutual exclusion behavior is controlled by the proposed periodic mutual exclusion supervisors. Finally, an example is used to illustrate the proposed methodology.

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GILET, TRISTAN, and JOHN W. M. BUSH. "The fluid trampoline: droplets bouncing on a soap film." Journal of Fluid Mechanics 625 (April 14, 2009): 167–203. http://dx.doi.org/10.1017/s0022112008005442.

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We present the results of a combined experimental and theoretical investigation of droplets falling onto a horizontal soap film. Both static and vertically vibrated soap films are considered. In the static case, a variety of behaviours were observed, including bouncing, crossing and partial coalescence. A quasi-static description of the soap film shape yields a force–displacement relation that provides excellent agreement with experiment, and allows us to model the film as a nonlinear spring. This approach yields an accurate criterion for the transition between droplet bouncing and crossing. Moreover, it allows us to rationalize the observed constancy of the contact time and scaling for the coefficient of restitution in the bouncing states. On the vibrating film, a variety of bouncing behaviours were observed, including simple and complex periodic states, multi-periodicity and chaos. A simple theoretical model is developed that captures the essential physics of the bouncing process, reproducing all observed bouncing states. The model enables us to rationalize the observed coexistence of multiple periodic bouncing states by considering the dependence of the energy transferred to the droplet on the phase of impact. Quantitative agreement between model and experiment is deduced for simple periodic modes, and qualitative agreement for more complex periodic and chaotic bouncing states. Analytical solutions are deduced in the limit of weak forcing and dissipation, yielding insight into the contact time and periodicity of the bouncing states.

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Musumarra, Giuseppe. "Celebrating the 150th anniversary of the Periodic Table: an outlook in the circular economy era." Bullettin of the Gioenia Academy of Natural Sciences of Catania 53, no. 383 (January 11, 2020): FP1—FP10. http://dx.doi.org/10.35352/gioenia.v53i383.73.

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The first version of The Periodic Table elaborated by Mendeleev was published on February 17th 1869. To celebrate the 150th anniversary of this event, the United Nations declared 2019 as the International Year of the Periodic Table. This discovery was achieved as the conclusion of a long itinerary engaging several researchers investigating the periodicity in the properties of the chemical elements. In this process the Sicilian chemist Stanislao Cannizzaro provided a significant contribution. The impact of the Periodic Table on the scientific progress, as well as on the improvement of mankind life conditions and welfare, has been enormous. However, the increasing recognition of the limted resources of our planet, nowadays requires a change of paradigm from linear to circular economy. In order to tackle such a complex problem, the data reported in the traditional Periodic Table need to be integrated by information regarding the elements availability in nature, the sustainability of the processes, and the recycling possibility. Examples regarding lithium, cobalt, and rare earth elements are reported.

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Pan, Yangdong, ChangKyoo Yoo, Jay H. Lee, and In-Beum Lee. "Process monitoring for continuous process with periodic characteristics." Journal of Chemometrics 18, no. 2 (February 2004): 69–75. http://dx.doi.org/10.1002/cem.848.

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Moreno-Risueno, Miguel A., Jaimie M. Van Norman, Antonio Moreno, Jingyuan Zhang, Sebastian E. Ahnert, and Philip N. Benfey. "Oscillating Gene Expression Determines Competence for Periodic Arabidopsis Root Branching." Science 329, no. 5997 (September 9, 2010): 1306–11. http://dx.doi.org/10.1126/science.1191937.

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Plants and animals produce modular developmental units in a periodic fashion. In plants, lateral roots form as repeating units along the root primary axis; however, the developmental mechanism regulating this process is unknown. We found that cyclic expression pulses of a reporter gene mark the position of future lateral roots by establishing prebranch sites and that prebranch site production and root bending are periodic. Microarray and promoter-luciferase studies revealed two sets of genes oscillating in opposite phases at the root tip. Genetic studies show that some oscillating transcriptional regulators are required for periodicity in one or both developmental processes. This molecular mechanism has characteristics that resemble molecular clock–driven activities in animal species.

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Zhou, Ruo-Wei, Guang-Yan Zhong, Jiang-Cheng Li, Yun-Xian Li, and Feng He. "Stochastic resonance of periodic volatility in financial markets with stock crashes." Modern Physics Letters B 32, no. 24 (August 27, 2018): 1850290. http://dx.doi.org/10.1142/s0217984918502901.

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We investigate the stochastic resonance of periodic volatility in two financial markets with stock crashes for Dow Jones component stocks and Hang Seng index, based on the modified Heston model with an effective potential to describe the stock crashes. We introduce a cosine term to Heston model and develop a modified Heston model with periodic stochastic volatility for capturing the periodicity of the volatility process or volatility clustering which was observed in historical financial data sets. The proposed model was tested against Dow Jones industrial and Hang Seng index data. The experimental results demonstrate that the proposed model fits the historical data well when compared with the original Heston model. The signal power amplification (SPA) is calculated and studied to investigate the stochastic resonance of the proposed dynamic system. Experimental results suggest that: (i) optimal values of volatility parameters can be identified which maximize the effects of systematic and non-systematic randomness to the market periodicity; (ii) different values of correlation strength between noise sources will cause critical phenomenon and induce single or multiple resonances.

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Dasbach, Michael, Hendrik M. Reinhardt, and Norbert A. Hampp. "Formation of Highly Ordered Platinum Nanowire Arrays on Silicon via Laser-Induced Self-Organization." Nanomaterials 9, no. 7 (July 18, 2019): 1031. http://dx.doi.org/10.3390/nano9071031.

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Laser-induced periodic surface structures (LIPSS) provide an elegant solution for the generation of highly ordered periodic patterns on the surface of solids. In this study, LIPSS are utilized for the formation of periodic platinum nanowire arrays. In a process based on laser-stimulated self-organization, platinum thin films, sputter-deposited onto silicon, are transformed into nanowire arrays with an average periodicity of 538 nm. The width of the platinum nanowires is adjustable in a range from 20 nm to 250 nm by simply adjusting the thickness of the initial platinum thin films in a range from 0.3 nm to 4.3 nm. With increasing width, platinum nanowires show a rising tendency to sink into the surface of the silicon wafer, thus indicating alloying between platinum and silicon upon LIPSS-formation by a nanosecond-pulsed laser. The Pt/silicon wires may be etched away, leaving a complementary nanostructure in the silicon surface.

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Kempa, Thomas J., D. Kwabena Bediako, Sun-Kyung Kim, Hong-Gyu Park, and Daniel G. Nocera. "High-throughput patterning of photonic structures with tunable periodicity." Proceedings of the National Academy of Sciences 112, no. 17 (April 13, 2015): 5309–13. http://dx.doi.org/10.1073/pnas.1504280112.

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A patterning method termed “RIPPLE” (reactive interface patterning promoted by lithographic electrochemistry) is applied to the fabrication of arrays of dielectric and metallic optical elements. This method uses cyclic voltammetry to impart patterns onto the working electrode of a standard three-electrode electrochemical setup. Using this technique and a template stripping process, periodic arrays of Ag circular Bragg gratings are patterned in a high-throughput fashion over large substrate areas. By varying the scan rate of the cyclically applied voltage ramps, the periodicity of the gratings can be tuned in situ over micrometer and submicrometer length scales. Characterization of the periodic arrays of periodic gratings identified point-like and annular scattering modes at different planes above the structured surface. Facile, reliable, and rapid patterning techniques like RIPPLE may enable the high-throughput and low-cost fabrication of photonic elements and metasurfaces for energy conversion and sensing applications.

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GAYER, TOBIAS. "CONTROLLABILITY AND INVARIANCE PROPERTIES OF TIME-PERIODIC SYSTEMS." International Journal of Bifurcation and Chaos 15, no. 04 (April 2005): 1361–75. http://dx.doi.org/10.1142/s021812740501265x.

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In this paper, control sets, i.e. maximal subsets of approximate controllability, are introduced for time-periodic parameter dependent systems with open loop control. It is shown that the time-periodicity causes some special topological properties of control sets that influence their merging and bifurcation process. These properties allow an enhancement of the available set-oriented numerical methods for the approximation of control sets. For the application of these methods, the so-called inner-pair condition must be satisfied. It is shown that this condition holds for a wide class of time-periodic control-affine systems that includes, for instance, coupled excited oscillators if the number of controls equals the degrees of freedom. The application of the methods to the controlled escape equation with periodic driving term where the parameter acts on the control range gives insight into the changing dynamics and different types of mergers of control sets.

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Tsybulkin, G. A. "Study of pulsed arc processes at periodic switching of volt-ampere characteristics of arc power source." Paton Welding Journal 2019, no. 7 (July 28, 2019): 2–6. http://dx.doi.org/10.15407/tpwj2019.07.01.

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Wang, Zengyun, Jinde Cao, Zuowei Cai, and Lihong Huang. "Periodicity and fixed-time periodic synchronization of discontinuous delayed quaternion neural networks." Journal of the Franklin Institute 357, no. 7 (May 2020): 4242–71. http://dx.doi.org/10.1016/j.jfranklin.2020.01.005.

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Haupaix, Nicolas, Camille Curantz, Richard Bailleul, Samantha Beck, Annie Robic, and Marie Manceau. "The periodic coloration in birds forms through a prepattern of somite origin." Science 361, no. 6408 (September 20, 2018): eaar4777. http://dx.doi.org/10.1126/science.aar4777.

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The periodic stripes and spots that often adorn animals’ coats have been largely viewed as self-organizing patterns, forming through dynamics such as Turing’s reaction-diffusion within the developing skin. Whether preexisting positional information also contributes to the periodicity and orientation of these patterns has, however, remained unclear. We used natural variation in colored stripes of juvenile galliform birds to show that stripes form in a two-step process. Autonomous signaling from the somite sets stripe position by forming a composite prepattern marked by the expression profile of agouti. Subsequently, agouti regulates stripe width through dose-dependent control of local pigment production. These results reveal that early developmental landmarks can shape periodic patterns upstream of late local dynamics, and thus constrain their evolution.

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Shechtman, Dan, and Candace I. Lang. "Quasiperiodic Materials: Discovery and Recent Developments." MRS Bulletin 22, no. 11 (November 1997): 40–42. http://dx.doi.org/10.1557/s0883769400034412.

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The mid 1980s benefited from three major scientific announcements that altered our world view on the structure of matter and its properties. These were the discovery of quasiperiodic crystals (QCs), which are commonly referred to as quasicrystals (1984), fullerenes (1985), and high-temperature superconductivity (1986). The discovery of QC was announced to a community active in the mature science of crystallography. Crystallographers, and other scientists who studied the structure of matter and its defects, relied on a series of laws and paradigms undisputed since von Laue performed his first x-ray-diffraction experiments in 1912. One leading paradigm stated that the atomic structure of a crystal is ordered and periodic. Explanations of this paradigm, based on common sense, could be summarized as, “It is periodic because it is ordered.”Periodicity implies a set of specific rules, among them the allowed rotational symmetries—namely one-, two-, three-, four-, and sixfold. Fivefold rotational symmetry is excluded. Past textbooks specified this, stating that fivefold rotational symmetry is impossible in periodic structures. Other books stated the impossibility of such symmetry in crystals.Paradigms are based on experience rather than on a rigorous, scientific study process. Therefore when proven wrong, they are difficult to uproot. From 1912 to 1984, nothing shook the paradigm, “Order in crystals is periodicity.” Incommensurate structures challenged the paradigm for a while but were soon found to be a modulation of periodic crystals, saving the paradigm. However in the background, a series of articles broadened the scope of crystallography into hyperspace and prepared the mathematical platform from which the science of quasiperiodicity in crystals could take off.

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De Ridder, F., A. de Brauwere, R. Pintelon, J. Schoukens, and F. Dehairs. "Identification of the accretion rate for annually resolved archives." Biogeosciences Discussions 3, no. 2 (April 10, 2006): 321–44. http://dx.doi.org/10.5194/bgd-3-321-2006.

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Abstract. The past environment is often reconstructed by measuring a given proxy (e.g. δ18O) in an environmental archive, i.e. a species which gradually accumulates mass and records the current environment during this mass formation (e.g. corals, shells, trees, etc...). When such an environmental proxy is measured, its values are known as a function of distance. However, to relate the data to environmental variations, the date associated with each measurement, i.e. the time base, should be known. This is not straightforward solved, since species usually do not grow at constant rates. In this paper, we investigate this problem for annually resolved archives, which exhibit a certain periodicity. Such signals are often found in clams or corals. Due to variations in accretion rate the data along the distance axis have a disturbed periodic profile. A method is developed to extract information about the accretion rate, such that the original (periodic) signal as function of time can be recovered. Simultaneously the exact shape of the periodic signal is estimated. The final methodology is quasi-independent of choices made by the investigator. Every step in the procedure is described in detail and finally, the method is exemplified on a real world example.

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Nieken, Ulrich, and Otto Watzenberger. "Periodic operation of the Deacon process." Chemical Engineering Science 54, no. 13-14 (July 1999): 2619–26. http://dx.doi.org/10.1016/s0009-2509(98)00490-4.

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Fusaoka, Takahiro, Shigeo KIMURA, Atsushi OKAJIMA, and Takahiro KIWATA. "Numerical Simulation of Periodic Solidifying Process." Proceedings of thermal engineering conference 2002 (2002): 237–38. http://dx.doi.org/10.1299/jsmeptec.2002.0_237.

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Borodin, Alexei. "Periodic Schur process and cylindric partitions." Duke Mathematical Journal 140, no. 3 (December 2007): 391–468. http://dx.doi.org/10.1215/s0012-7094-07-14031-6.

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He, Chuanqi. "Periodic table of human civilization process." Educational Philosophy and Theory 52, no. 8 (July 22, 2019): 848–68. http://dx.doi.org/10.1080/00131857.2019.1642197.

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Zhu, Youfeng, Zibo Wang, Qiang Wang, Xinhua Liu, Hongyu Zang, and Liang Wang. "Nonlinear Dynamic Analysis of Rotor Rub-Impact System." Shock and Vibration 2019 (November 29, 2019): 1–20. http://dx.doi.org/10.1155/2019/4867364.

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A dynamic model of a double-disk rub-impact rotor-bearing system with rubbing fault is established. The dynamic differential equation of the system is solved by combining the numerical integration method with MATLAB. And the influence of rotor speed, disc eccentricity, and stator stiffness on the response of the rotor-bearing system is analyzed. In the rotor system, the time history diagram, the axis locus diagram, the phase diagram, and the Poincaré section diagram in different rotational speeds are drawn. The characteristics of the periodic motion, quasiperiodic motion, and chaotic motion of the system in a given speed range are described in detail. The ways of the system entering and leaving chaos are revealed. The transformation and evolution process of the periodic motion, quasiperiodic motion, and chaotic motion are also analyzed. It shows that the rotor system enters chaos by the way of the period-doubling bifurcation. With the increase of the eccentricity, the quasi-periodicity evolution is chaotic. The quasiperiodic motion evolves into the periodic three motion phenomenon. And the increase of the stator stiffness will reduce the chaotic motion period.

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Okamoto, Ken, and Koichi Morishige. "Polishing Process Automation by Industrial Robot with Polished Surface Quality Judgment Based on Image Processing - Visual Inspection Based on Pattern Matching." Key Engineering Materials 523-524 (November 2012): 481–86. http://dx.doi.org/10.4028/www.scientific.net/kem.523-524.481.

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This study deals with automation of polishing process by using an industrial robot. In polishingprocess, full automation of polishing operation has not been achieved due to the difficulty invisual inspection. Judgment of whether polishing is sufficient or not has been performed by skilledworkers. In this study, the polishing after milling process is targeted. In the previous report, the generationof robot program for polishing operation based on CAD data was already proposed. Focusingon the periodicity of cutter mark patterns on milling surface, we proposed an automatic judgment ofpolished surface quality based on the image processing which uses Discrete Fourier Transformation.In order to capture images of polished surface, a CCD camera was mounted at 6-axis controlled robothand. However, the image processing method proposed in previous report could not judge the curvedcutter mark patterns because the periodicity of those patterns is not uniform. The objective of thisreport is the development of automatic judgment method for non-periodic cutter mark patterns. Wedeveloped judgment method which uses pattern recognition as a mean to judge existence or not of cuttermarks. As a result, the developed system allows the automatic polishing that includes the surfacequality judgment.

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Dinger, Florian, Stefan Bredemeyer, Santiago Arellano, Nicole Bobrowski, Ulrich Platt, and Thomas Wagner. "On the link between Earth tides and volcanic degassing." Solid Earth 10, no. 3 (May 29, 2019): 725–40. http://dx.doi.org/10.5194/se-10-725-2019.

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Abstract. Long-term measurements of volcanic gas emissions conducted during the last decade suggest that under certain conditions the magnitude or chemical composition of volcanic emissions exhibits periodic variations with a period of about 2 weeks. A possible cause of such a periodicity can be attributed to the Earth tidal potential. The phenomenology of such a link has been debated for long, but no quantitative model has yet been proposed. The aim of this paper is to elucidate whether a causal link between tidal forcing and variations in volcanic degassing can be traced analytically. We model the response of a simplified magmatic system to the local tidal gravity variations and derive a periodical vertical magma displacement in the conduit with an amplitude of 0.1–1 m, depending on the geometry and physical state of the magmatic system. We find that while the tide-induced vertical magma displacement presumably has no significant direct effect on the volatile solubility, the differential magma flow across the radial conduit profile may result in a significant increase in the bubble coalescence rate at a depth of several kilometres by up to several multiples of 10 %. Because bubble coalescence facilitates separation of gas from magma and thus enhances volatile degassing, we argue that the derived tidal variation may propagate to a manifestation of varying volcanic degassing behaviour. The presented model provides a first basic framework which establishes an analytical understanding of the link between the Earth tides and volcanic degassing.

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Rigall, Tommy, Benjamin Cotté, and Philippe Lafon. "Low-Noise Synthetic Turbulence Tailored to Lateral Periodic Boundary Conditions." Fluids 6, no. 6 (May 21, 2021): 193. http://dx.doi.org/10.3390/fluids6060193.

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The present work is dedicated to turbulence synthesis tailored to lateral periodic boundary conditions for direct noise computations through compressible large eddy simulations. Synthetic turbulence can be essential for aeroacoustic applications when computing airfoil turbulent inflow noise or for accurately capturing the behavior of boundary layers. This behavior determines both trailing edge noise and complex flow structures such as laminar separation bubbles. For airfoil simulation purposes, spanwise periodic boundary conditions are usually considered. If synthetic perturbations are injected without observing the periodicity rule, strong spurious pressure waves are emitted and pollute the entire computational domain. In this work, the random Fourier modes method for turbulence generation is adapted in order to respect the spanwise periodicity constraint right at the computational domain inlet. This approach does not affect the turbulence properties such as the spectral shape and the turbulent kinetic energy decay. Since the emphasis is put on the generation and convection of the turbulence, only the turbulence convection region between the inlet and the airfoil is considered in this paper, without the airfoil. Two geometrical configurations are tested: the first one is a simple box with a constant mesh size, and the second one concentrates the fine cells on the area in front of the airfoil. In the second configuration, the computational cost is reduced by up to 25%, but more spurious noise is present because of interpolation areas between different grids using the Chimera method. Finally, the results’ reproducibility is assessed using different turbulence realizations.

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Liu, Tingting, and Suvi Gezari. "Supermassive Black Hole Binary Candidates from the Pan-STARRS1 Medium Deep Survey." Proceedings of the International Astronomical Union 13, S338 (October 2017): 46–52. http://dx.doi.org/10.1017/s1743921318003617.

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AbstractWe conducted a systematic search for periodically varying quasars, which are predicted manifestations of sub-pc supermassive black hole binaries (SMBHBs), in the Pan-STARRS1 Medium Deep Survey (PS1 MDS). Since the normal variability of quasars can also mimic periodicity over a small number of cycles, we have extended the temporal baseline by monitoring the candidates with the Discovery Channel Telescope and the Las Cumbres Observatory telescopes. We have also adopted a more rigorous method to evaluate the significance of the periodic candidates, by considering in the light curves a “red noise” background modeled as the Damped Random Walk process. While none of the candidates can be resolved by the current pulsar timing arrays (PTAs) as individual gravitational wave sources, the Large Synoptic Survey Telescope is capable of finding more periodic candidates, some of which are likely to be detected by the PTA experiment with the Square Kilometre Array.

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Dominic, Priya, Florent Bourquard, Stéphanie Reynaud, Arnaud Weck, Jean-Philippe Colombier, and Florence Garrelie. "On the Insignificant Role of the Oxidation Process on Ultrafast High-Spatial-Frequency LIPSS Formation on Tungsten." Nanomaterials 11, no. 5 (April 22, 2021): 1069. http://dx.doi.org/10.3390/nano11051069.

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The presence of surface oxides on the formation of laser-induced periodic surface structures (LIPSS) is regularly advocated to favor or even trigger the formation of high-spatial-frequency LIPSS (HSFL) during ultrafast laser-induced nano-structuring. This paper reports the effect of the laser texturing environment on the resulting surface oxides and its consequence for HSFLs formation. Nanoripples are produced on tungsten samples using a Ti:sapphire femtosecond laser under atmospheres with varying oxygen contents. Specifically, ambient, 10 mbar pressure of air, nitrogen and argon, and 10−7 mbar vacuum pressure are used. In addition, removal of any native oxide layer is achieved using plasma sputtering prior to laser irradiation. The resulting HSFLs have a sub-100 nm periodicity and sub 20 nm amplitude. The experiments reveal the negligible role of oxygen during the HSFL formation and clarifies the significant role of ambient pressure in the resulting HSFLs period.

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Rudenko, Anton, Cyril Mauclair, Florence Garrelie, Razvan Stoian, and Jean-Philippe Colombier. "Self-organization of surfaces on the nanoscale by topography-mediated selection of quasi-cylindrical and plasmonic waves." Nanophotonics 8, no. 3 (January 29, 2019): 459–65. http://dx.doi.org/10.1515/nanoph-2018-0206.

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AbstractUsing coupled electromagnetic and hydrodynamic calculations, we elucidate theoretically the topographic transition from a random metallic surface to a periodic sub-wavelength grating by ultrashort laser ablation. The origin of this transition lies in the successive selection of hybrid surface waves scattered by random nanoholes. Contrary to the common belief that surface plasmon polaritons play the dominant role in the process and define the grating periodicity, we show that both quasi-cylindrical and surface plasmon waves are involved, whereas the diversity in the resulting spacings λ/2–λ (λ is the laser wavelength) is the manifestation of a broad frequency overlap of these waves, controlled by their relative phase shifts with respect to the plasmonic counterparts. The topography evolution imposes the dominant contribution to the surface sub-wavelength pattern by selecting the appropriate wave character from plasmonic modes to evanescent cylindrical waves. With the radiation dose, the grating periodicity exhibits a pronounced blue shift due to reinforced dipole–dipole coupling between the nanoholes and surface curvatures in the laser-processed area. This allows the creation of regular patterns with tunable periodicity.

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Shield, J. E., and M. J. Kramer. "Deformation-induced planar defects in Al–Cu–Fe quasicrystals." Journal of Materials Research 12, no. 2 (February 1997): 300–303. http://dx.doi.org/10.1557/jmr.1997.0039.

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Planar defects were observed in a hot isostatically pressed Al–Cu–Fe alloy. The defects were determined to be perpendicular to the fivefold direction. They were also found to be regions where the quasiperiodicity in the five-fold direction was disrupted, resulting in a periodicity along this direction of 1.06 nm. The defects were stable up to approximately 750 °C. The defects were determined to be formed by the applied shear forces associated with the consolidation process. The displacement vector of the defects was determined to be in a twofold direction perpendicular to the periodic direction.

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Sone, Yasutomo, Junichi Suzumura, Naoya Kamura, and Toshihiko Sasaki. "Identification of Iron Rusts on Rail by X-Ray Diffraction and Vibrational Analysis." Advanced Materials Research 409 (November 2011): 581–85. http://dx.doi.org/10.4028/www.scientific.net/amr.409.581.

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A periodical unevenness of the running surface of rails is formed on ascending slope of submarine railway tunnel. One of the causes has been concluded due to the combination of a low friction and wheel load variation induced by some kinds of iron oxides and oxyhydroxides with various coefficients of friction on the rail, though it has not been made clear yet. In this study, X-ray diffraction and Raman scattering spectroscopic analysis were attempted to identify iron rusts on the rail as a process to solve the periodic unevenness of the rail suffering many railway companies.

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DITLEVSEN, PETER D., and HOLGER BRAUN. "PSEUDO-RESONANCE INDUCED QUASI-PERIODIC BEHAVIOR IN STOCHASTIC THRESHOLD DYNAMICS." Stochastics and Dynamics 11, no. 02n03 (September 2011): 315–21. http://dx.doi.org/10.1142/s0219493711003309.

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Here we present a simple stochastic threshold model consisting of a deterministic slowly decaying term and a fast stochastic noise term. The process shows a pseudo-resonance, in the sense that for small and large intensities of the noise the signal is irregular and the distribution of threshold crossings is broad, while for a tuned intermediate value of noise intensity, the signal becomes quasi-periodic and the distribution of threshold crossings is narrow. The mechanism captured by the model might be relevant for explaining apparent quasi-periodicity of observed climatic variations where no internal or external periodicities can be identified.

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Keenan, Patricia. "Periodic Performance Review in the Accreditation Process." Journal of Radiology Nursing 25, no. 1 (March 2006): 13–15. http://dx.doi.org/10.1016/j.jradnu.2005.12.003.

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Iqbal, Amer, Can Kozçaz, and Tanweer Sohail. "Periodic Schur process, cylindric partitions and theory." Nuclear Physics B 844, no. 2 (March 2011): 334–47. http://dx.doi.org/10.1016/j.nuclphysb.2010.11.006.

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Sterman, Leah E., and B. Erik Ydstie. "The steady-state process with periodic perturbations." Chemical Engineering Science 45, no. 3 (1990): 721–36. http://dx.doi.org/10.1016/0009-2509(90)87014-j.

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Zhukov, V. P. "Calculation of the periodic powder screening process." Chemical and Petroleum Engineering 28, no. 1 (January 1992): 32–34. http://dx.doi.org/10.1007/bf01156705.

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Mattioda, Fernanda, Luiz Mario de Matos Jorge, and Regina Maria Matos Jorge. "Wheat hydration process intensification by periodic operation." Journal of Food Engineering 246 (April 2019): 153–59. http://dx.doi.org/10.1016/j.jfoodeng.2018.11.012.

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Guo, Ye, Ke Liu, and Zeyun Yu. "Tetrahedron-Based Porous Scaffold Design for 3D Printing." Designs 3, no. 1 (February 18, 2019): 16. http://dx.doi.org/10.3390/designs3010016.

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Tissue repairing has been the ultimate goal of surgery, especially with the emergence of reconstructive medicine. A large amount of research devoted to exploring innovative porous scaffold designs, including homogeneous and inhomogeneous ones, have been presented in the literature. The triply periodic minimal surface has been a versatile source of biomorphic structure design due to its smooth surface and high interconnectivity. Nonetheless, many 3D models are often rendered in the form of triangular meshes for its efficiency and convenience. The requirement of regular hexahedral meshes then becomes one of limitations of the triply periodic minimal surface method. In this paper, we make a successful attempt to generate microscopic pore structures using tetrahedral implicit surfaces. To replace the conventional Cartesian coordinates, a new coordinates system is built based on the perpendicular distances between a point and the tetrahedral faces to capture the periodicity of a tetrahedral implicit surface. Similarly to the triply periodic minimal surface, a variety of tetrahedral implicit surfaces, including P-, D-, and G-surfaces are defined by combinations of trigonometric functions. We further compare triply periodic minimal surfaces with tetrahedral implicit surfaces in terms of shape, porosity, and mean curvature to discuss the similarities and differences of the two surfaces. An example of femur scaffold construction is provided to demonstrate the detailed process of modeling porous architectures using the tetrahedral implicit surface.

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Journal articles on the topic 'Processi periodici'

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