2,970 research outputs found
Numerical Study of Droplet Generation in A Complex Micro-Channel
Small liquid drops have many applications in science and technology. In microfluidics research, microscopic drops are used to facilitate micromixing, loading and dispensing reagents from micro-reactors, or to improve the efficiency of cell sorting and fluid sampling systems. Many factors can affect the microdrop generation, such as fluid rheology, flow speed, and interaction of the fluid(gas)-fluid interface with the channel walls. In this paper, a numerical study of the generation of microscopic droplets in a micro-channel of complex geometry is presented. The multiphase flow with interface in complex micro-channel is described by a coupled immersed boundary and level-set frontcapturing methods. Comparison of the simulation with experimental results is also presented
Structure-specified H∞ loop shaping control for balancing of bicycle robots: A particle swarm optimization approach
In this paper, the particle swarm optimization (PSO) algorithm was used to design the structure-specified H∞ loop shaping controllers for balancing of bicycle robots. The structure-specified H∞ loop shaping controller design normally leads to a complex optimization problem. PSO is an efficient meta-heuristic search which is used to solve multi-objectives and non-convex optimizations. A model-based systematic procedure for designing the particle swarm optimization-based structure-specified H∞ loop shaping controllers was proposed in this research. The structure of the obtained controllers are therefore simpler. The simulation and experimental results showed that the robustness and efficiency of the proposed controllers was gained when compared with the proportional plus derivative (PD) as well as conventional H∞ loop shaping controller. The simulation results also showed a better efficiency of the developed control algorithm compared to the Genetic Algorithm based one
Necessary Conditions for Non-Intersection of Collections of Sets
This paper continues studies of non-intersection properties of finite
collections of sets initiated 40 years ago by the extremal principle. We study
elementary non-intersection properties of collections of sets, making the core
of the conventional definitions of extremality and stationarity. In the setting
of general Banach/Asplund spaces, we establish new primal (slope) and dual
(generalized separation) necessary conditions for these non-intersection
properties. The results are applied to convergence analysis of alternating
projections.Comment: 26 page
Liminal experience of East Asian backpackers
Acknowledging the increasing popularity of independent travel from East Asia, this article explores the backpacking experience of young travellers of the region, from a socio-anthropological angle. Using liminality theory as a guideline and adopting a qualitative investigative approach, 31 interviews with East Asian backpackers were conducted. The findings suggest there are dual facets of the liminal experiences of the backpackers. On one hand, young travellers were motivated to escape from temporal, spatial and social pressures at home. On the other, their narratives reflected a strong commitment to home through a sense of filial piety, an awareness of their identity and positive evaluation of home. These findings advance our understanding of the liminal experiences in an Asian backpacking context
A tracer study in a vertical flow constructed wetland treating septage
Purpose: This study aims to investigate the hydraulic behaviour of a pilot-scale, two-staged, vertical flow constructed wetland (VFCW) for septage treatment, in terms of factors such as hydraulic retention time and hydraulic loading rate and its influence on the treatment dynamics. Because of intermittent feeding mode of VFCW systems and variation in its loading, its hydraulic behaviour is highly variable and need to be understood to optimize its treatment performance. Design/methodology/approach: Tracer test were carried out using bromide ion with varying hydraulic loading rates (HLR) of 6.82 cm/d, 9.09 cm/d and 11.40 cm/d (i.e. equivalent to 75 L/d, 100L/d and 125 L/d). Tracer data is then analysed using the Residence Time Distribution (RTD) method. Findings: RTD analysis showed that the increase in HLR increases the average hydraulic retention time (HRT). Subsequently, the increase in HLR results in a lower recovery of effluent, resulting in poor productivity in treatment. The study also showed that the removal of nitrogen and organic matter improved with increasing HRT. However, observations show no correlation between HRT and total solids removal. Originality/value: A performance evaluation method (by tracer) is proposed to understand the hydraulics of flow in constructed wetlands, which has not been widely studied. Additionally, the dynamics of treatment in VFCWs treating septage may also be revealed by the tracer method. The study can be applied to any constructed wetlands designed for treatment of wastewater, septage or sludge
Earthquake Induced Slope Failure Simulation by SPH
Majority of slope stability, slope displacement and soil liquefaction analyses subjected to earthquake loading condition employed the finite element method (FEM) as the standard numerical tool. However, mechanism of soil failure in such condition often involved extremely large deformation and failure behaviors, which were unable to be modeled by FEM since this method was suffered from the grid distortion. In an attempt to overcome this limitation, we present herein our first attempt to extend the smoothed particle hydrodynamics (SPH) method to analyze slope failure behavior due to seismic shaking. For the sake of simplicity, effect of pore-water pressure was not taken into consideration. The numerical framework was then applied to simulate the failure behavior of a slope subjected to a seismic loading. Experimental model was also conducted to verify the numerical performance. It is shown that SPH can simulate fairly well the slope failure behavior in the model test, especially in prediction of the failure surface. The paper suggests that SPH should be considered as a powerful alternative for computation of geomaterials subjected to earthquake loading conditions
Growth and properties of subnanometer thin titanium nitride films
This research brings new insights into the relation between properties of ultra-thin conductive metal nitrides made by atomic layer deposition (ALD) and their possible industrial applications. The advantage of conductive nitrides over pure metals is (i) better established ALD processes allowing depositing high-quality films and (ii) the presence of nitrogen as an extra tool to manipulate the electron transport properties. In this work, we study titanium nitride (TiN) films with the aim to investigate the growth mechanism in combination with physical and electrical properties as a function of the layer thickness. In microelectronic devices, thin continuous TiN films are commonly used as diffusion barriers and metal gate material. Scaling electronic devices to nanometer dimensions requires a close look at electrical material properties as ultra-thin conductive materials encounter an insulating regime due to the depletion of carriers
In-plane elastic wave propagation and band-gaps in layered functionally graded phononic crystals
AbstractIn-plane wave propagation in layered phononic crystals composed of functionally graded interlayers arisen from the solid diffusion of homogeneous isotropic materials of the crystal is considered. Wave transmission and band-gaps due to the material gradation and incident wave-field are investigated. A classification of band-gaps in layered phononic crystals is proposed. The classification relies on the analysis of the eigenvalues of the transfer matrix for a unit-cell and the asymptotics derived for the transmission coefficient. Two kinds of band-gaps, where the transmission coefficient decays exponentially with the number of unit-cells are specified. The so-called low transmission pass-bands are introduced in order to identify frequency ranges, in which the transmission is sufficiently low for engineering applications, but it does not tend to zero exponentially as the number of unit-cells tends to infinity. A polyvalent analysis of the geometrical and physical parameters on band-gaps is presented
Deep Gaussian processes for regression using approximate expectation propagation
Deep Gaussian processes (DGPs) are multi-layer hierarchical generalisations
of Gaussian processes (GPs) and are formally equivalent to neural networks with
multiple, infinitely wide hidden layers. DGPs are nonparametric probabilistic
models and as such are arguably more flexible, have a greater capacity to
generalise, and provide better calibrated uncertainty estimates than
alternative deep models. This paper develops a new approximate Bayesian
learning scheme that enables DGPs to be applied to a range of medium to large
scale regression problems for the first time. The new method uses an
approximate Expectation Propagation procedure and a novel and efficient
extension of the probabilistic backpropagation algorithm for learning. We
evaluate the new method for non-linear regression on eleven real-world
datasets, showing that it always outperforms GP regression and is almost always
better than state-of-the-art deterministic and sampling-based approximate
inference methods for Bayesian neural networks. As a by-product, this work
provides a comprehensive analysis of six approximate Bayesian methods for
training neural networks
Snap-Stabilization in Message-Passing Systems
In this paper, we tackle the open problem of snap-stabilization in
message-passing systems. Snap-stabilization is a nice approach to design
protocols that withstand transient faults. Compared to the well-known
self-stabilizing approach, snap-stabilization guarantees that the effect of
faults is contained immediately after faults cease to occur. Our contribution
is twofold: we show that (1) snap-stabilization is impossible for a wide class
of problems if we consider networks with finite yet unbounded channel capacity;
(2) snap-stabilization becomes possible in the same setting if we assume
bounded-capacity channels. We propose three snap-stabilizing protocols working
in fully-connected networks. Our work opens exciting new research perspectives,
as it enables the snap-stabilizing paradigm to be implemented in actual
networks
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