Search results for " Bubble"

On Combinatorial Generation of Prefix Normal Words

2014

A prefix normal word is a binary word with the property that no substring has more 1s than the prefix of the same length. This class of words is important in the context of binary jumbled pattern matching. In this paper we present an efficient algorithm for exhaustively listing the prefix normal words with a fixed length. The algorithm is based on the fact that the language of prefix normal words is a bubble language, a class of binary languages with the property that, for any word w in the language, exchanging the first occurrence of 01 by 10 in w results in another word in the language. We prove that each prefix normal word is produced in O(n) amortized time, and conjecture, based on expe…

Not all bull and bear markets are alike: insights from a five-state hidden semi-Markov model

2022

This paper employs the hidden semi-Markov model and a novel model selection procedure to detect different states in the US stock market. The empirical results suggest that the market is switching between five states that can be classified into three bull states and two bear states. The three bull states are categorized as a low volatility bull market, a high volatility bull market, and a stock market bubble. One of the bear states represents a regular bear market, while the other one corresponds to either a stock market crash or a market correction. The paper demonstrates that the five-state model is consistent with a number of stylized facts and provides many valuable insights into the dyn…

2003

Analysis of joining and division of gas bubbles based on measurements of their motion trajectories

2014

The paper presents considerations on motion of a group of air bubbles. Special attention has been paid to interactions between them. The author presents the test stand structure and the idea of image tomograph used for measurements of bubble motion trajectories. The results of measurements have been presented in a three-dimensional space, and next characteristic behaviours of the moving bubbles were analyzed. Some basic mechanisms of the gas bubble division have been classified. DOI: http://dx.doi.org/10.5755/j01.mech.20.1.6596

Comparison between adaptive and uniform discontinuous Galerkin simulations in dry 2D bubble experiments

2013

Accepted by the Journal of Computational Physics Adaptive mesh refinement generally aims to increase computational efficiency without compromising the accuracy of the numerical solution. However it is an open question in which regions the spatial resolution can actually be coarsened without affecting the accuracy of the result. This question is investigated for a specific example of dry atmospheric convection, namely the simulation of warm air bubbles. For this purpose a novel numerical model is developed that is tailored towards this specific application. The compressible Euler equations are solved with a Discontinuous Galerkin method. Time integration is done with an IMEXmethod and the dy…

Periodic volcanic degassing behavior: The Mount Etna example

2013

[1] In contrast to the seismic and infrasonic energy released from quiescent and erupting volcanoes, which have long been known to manifest episodes of highly periodic behavior, the spectral properties of volcanic gas flux time series remain poorly constrained, due to a previous lack of hightemporal resolution gas-sensing techniques. Here we report on SO2 flux measurements, performed on Mount Etna with a novel UV imaging technique of unprecedented sampling frequency (0.5Hz), which reveal, for the first time, a rapid periodic structure in degassing from this target. These gas flux modulations have considerable temporal variability in their characteristics and involve two period bands: 40–250…

A NOVEL TECHNIQUE FOR MEASURING LOCAL BUBBLE SIZE DISTRIBUTION

2009

A novel experimental technique for measuring the local gas hold-up and the statistical distribution of local bubble size, is proposed. The technique is based on laser sheet illumination of the gas-liquid dispersion and synchronized camera, i.e. on equipment typically available in PIV set-ups. The liquid phase is made fluorescent by a suitable dye, and a band-pass optical filter is placed in front of the camera optics, in order to allow only fluoresced light to reach the camera CCD. In this way bubbles intercepted by the laser sheet are clearly identified thanks to the neat shade resulting in the images. This allows excluding from subsequent analysis all bubbles visible in the images but not…

Mass transfer and hydrodynamic characteristics of unbaffled stirred bio-reactors: Influence of impeller design

2014

Abstract Unbaffled stirred tanks are increasingly recognized as a viable alternative to common baffled tanks for a range of processes where the presence of baffles is undesirable for some reason. For instance, in the case of shear sensitive cell cultivation (e.g. human cells), unbaffled tanks have been recently found to be able to provide sufficient mass transfer through the free surface vortex. As a consequence the need for bubble formation and subsequent bursting, along with relevant cells damage, is conveniently avoided. In this work the influence of impeller geometry on mass transfer performance and power demand of an unbaffled stirred vessel operating both in sub-critical conditions (t…

Local gas-liquid hold-up and interfacial area via light sheet and image analysis

2010

Particle Image Velocimetry techniques coupled with advanced Image Processing tools are receiving an increasing interest for measuring flow quantities and local bubble-size distributions in gas-liquid contactors. In this work, an effective experimental technique for measuring local gas hold-up and interfacial area, as well as bubble size distribution, is discussed. The technique, hereafter referred to as Laser Induced Fluorescence with Shadow Analysis for Bubble Sizing (LIF-SABS) is based on laser sheet illumination of the gas-liquid dispersion and synchronized camera, i.e. on equipment typically available within PIV set-ups. The liquid phase is made fluorescent by a suitable dye, and an opt…

Costa Blanca: Urban Evolution of a Mediterranean Region through GIS Data

2015

This paper investigates the international retirement migration from elderly northern Europeans into Spain and its influence on expansion of urban sprawl there. Key themes analyzed in this paper include the urban sprawl expansion during the Spanish housing bubble, and the link between lifestyle migrants and urban sprawl development. This paper considers the reasons for moving to Spain, which are chiefly related with the climate and lifestyle. It also explores the benefits and drawbacks of these en masse lifestyle migration and the environmental and landscape impacts on Mediterranean Spain. In order to visualize better this international migration we have created some GIS maps from a GIS proj…