Dissipative particle dynamics simulation of flow in periodically grooved three-dimensional nano- and micro-channels

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.Nonequillibrium flow in three-dimensional grooved nano- and micro-channels is investigated using the Dissipative Particle Dynamics simulation method. Roughness is introduced by periodically placing rectangular protruding elements on the upper channel wall. The protrusion length and height are varied and their effect on the flow is examined. The computed macroscopic quantities of practical interest include density, velocity, pressure, and temperature profiles as well as relations between the friction factor and the Reynolds number. When compared to the smooth channel case, lower flow velocities are observed in the central part of the channel for all cases studied. This reduction of velocities becomes more pronounced as the protrusion height increases. For the micro-channel, density, pressure and temperature remain almost constant in the central part of the channel and their pattern near and inside the cavities depend on the protrusion shape. In the nanochannel case, lower temperatures and pressures are observed for all grooved channels relative to the smooth channel case. For all channel cases studied the calculated friction factor decreases as Reynolds number increases, following a power law relation

Transport properties of fluids in nanochannels: bridging nano to macro

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.A method of calculating transport properties in nanochannels is presented in this work. The Molecular Dynamics simulation of a system of liquid argon flowing in a nanochannel formed by krypton walls was the basis for our analysis concerning transport properties and specifically diffusion coefficient, shear viscosity and thermal conductivity. It is shown that for confined systems, such as nanochannels, if one of the transport properties is known, then the others can be estimated. The simulation results reveal that all properties approach bulk values at relatively small channel widths, at about 6-7nm. Below this critical point, the wall effect on fluid atoms is strong and the transport properties change dramatically. In order to extend the calculations over rough-wall nanochannels, we apply the relation extracted for flat wall channels to channels with walls consisted of successive rectangular protrusions and cavities

Transport properties and structure of fluids in hydrophobic/hydrophilic nanochannels

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.When downsizing towards the nanoscale, system dimensions have been found to affect channel flows mainly because of the presence of the walls that interact strongly with fluid particles. Parameters which are not taken into account at the classical theory continuum theory at the macroscale, should be taken into account at the nano or even micro-scale where the surface to volume ratio increases significantly. Such property is the wall/fluid interaction which determines the wetting (hydrophilic behavior) or not (hydrophobic behavior) of a surface. We first investigate the effect of wall/fluid interaction on fluid atom distribution near the wall through the radial distribution function and, next, we calculate the three most important fluid transport properties, i.e., the diffusion coefficient, shear viscosity and thermal conductivity. Transport properties seem to be affected significantly in the channel region adjacent to the wall

A Protocol for the Secure Linking of Registries for HPV Surveillance

In order to monitor the effectiveness of HPV vaccination in Canada the linkage of multiple data registries may be required. These registries may not always be managed by the same organization and, furthermore, privacy legislation or practices may restrict any data linkages of records that can actually be done among registries. The objective of this study was to develop a secure protocol for linking data from different registries and to allow on-going monitoring of HPV vaccine effectiveness.A secure linking protocol, using commutative hash functions and secure multi-party computation techniques was developed. This protocol allows for the exact matching of records among registries and the computation of statistics on the linked data while meeting five practical requirements to ensure patient confidentiality and privacy. The statistics considered were: odds ratio and its confidence interval, chi-square test, and relative risk and its confidence interval. Additional statistics on contingency tables, such as other measures of association, can be added using the same principles presented. The computation time performance of this protocol was evaluated.The protocol has acceptable computation time and scales linearly with the size of the data set and the size of the contingency table. The worse case computation time for up to 100,000 patients returned by each query and a 16 cell contingency table is less than 4 hours for basic statistics, and the best case is under 3 hours.A computationally practical protocol for the secure linking of data from multiple registries has been demonstrated in the context of HPV vaccine initiative impact assessment. The basic protocol can be generalized to the surveillance of other conditions, diseases, or vaccination programs

Detection of low-dimensional chaos in wind time series

In the present work we investigated the existence of low-dimensional deterministic chaos in wind time series. The time series were obtained from the New Anchialos (Greece) Air Base Measurement station. In a first place we used the raw data without any noise filtering. Characteristic times were extracted using power spectrum and average mutual information function. The estimation of invariant measures, such as the correlation dimension and Lyapunov exponents indicate the possible existence of a low-dimensional attractor. After noise removal with the use of the local projective method the analysis indicates in a more clear way the existence of a low-dimensional attractor. In addition, the null hypothesis was tested for the dynamical characteristics of the wind time series by using the surrogate data test and the corresponding results provide significant evidence for the existence of low-dimensional chaotic dynamics underlying the wind time series. (C) 2008 Elsevier Ltd. All rights reserved

Privacy preserving record linkage using phonetic codes

Phonetic codes such as Soundex and Metaphone have been used in the past to address the Record Linkage Problem. However, to the best of our knowledge, no particular effort has been made within this context towards privacy assurance during the matching process. Phonetic codes have an interesting feature which can be cornerstone to providing privacy. They are mappings of strings which do not exhibit the one-to-one property. In this paper, we present a novel protocol for achieving privacy preserving record linkage using phonetics, we provide proof of correctness for our approach and finally we illustrate experimental results concerning performance and matching accuracy. The proposed protocol can be equally well applied to codes different than the phonetic ones, which do not exhibit the one-to-one property, such as hash tables with comparable results. © 2009 IEEE

Backward Degree a new index for online and offline change point detection based on complex network analysis

How to identify an upcoming transition in a time series continues to be an important open research issue. In various fields of physical sciences, engineering, finance and neuroscience abrupt changes can occur unexpectedly and are difficult to manage during the temporal evolution of the dynamic system. In this work, we developed a new unsupervised method called “Backward Degree” based on a new topological graph index that we introduce, which can be used to detect not only offline point of change, but also can effectively be used as an early warning system for online detection of upcoming abrupt changes. Specifically, based on the well-established algorithm “Visibility graph”, which was introduced by Lacasa et al. (2008) we convert a time series into a complex network and then we apply our proposed approach. The results, on a number of synthetic and financial datasets demonstrate that the proposed methodology correctly identifies change points during the evolution of time series validating the advantages of the proposed methodology for effective detection an upcoming abrupt transitions. © 2022 Elsevier B.V

Detection of jet axis in a horizontal turbulent jet via nonlinear analysis of minimum/maximum temperature time series

We have analyzed experimental temperature time series from a horizontal turbulent heated jet, in order to identify the jet axis location using non linear measures. The analysis was applied on both, the original time series as well as on the extreme value (minimum and maximum values) time series. In our analysis we employed mainly nonlinear measures such as mutual information and cumulative mutual information. The results show that the analysis of the extreme values time series using cumulative mutual information permits to distinguish the jet axis time series from the rest of the jet, as well as discriminate regions of the jet located close to jet axis or close to the boundaries. Furthermore, it is of interest that the application of simple statistical measures and clustering techniques shows that the use of extremes time series let us distinguish with greater confidence the jet axis than the use of the original one. © 2019 CHAOS 2011 - 4th Chaotic Modeling and Simulation International Conference, Proceedings. All rights reserved