Accuracy of bubble velocity measurement with a four-point optical fibre probe

For the operation of high void fraction bubbly flows in bubble\ud columns, insight in primary parameters such as bubble size,\ud shape and velocity as well as gas volume fraction is essential.\ud At high gas volume fractions the flow system becomes\ud opaque, ruling out non-intrusive optical techniques. As an\ud alternative optical fibre probes can be used, which have the\ud advantage of low cost, simplicity of setup and easy\ud interpretation of the results.\ud By using four-point optical fibre probe, properties of bubbles\ud can be studied, such as bubble velocity, bubble size, etc.\ud However, the effect of bubble wobbling behaviour and\ud physical properties of liquids on the accuracy of the velocity\ud measurements has not been investigated in detail.\ud In the present study, the performance of a four-point optical\ud fibre probe was evaluated for five different liquids. The probe\ud performance and causes of inaccuracies are discuss

Formation of Nanopillar Arrays in Ultrathin Viscous Films: The Critical Role of Thermocapillary Stresses

Experiments by several groups during the past decade have shown that a molten polymer nanofilm subject to a large transverse thermal gradient undergoes spontaneous formation of periodic nanopillar arrays. The prevailing explanation is that coherent reflections of acoustic phonons within the film cause a periodic modulation of the radiation pressure which enhances pillar growth. By exploring a deformational instability of particular relevance to nanofilms, we demonstrate that thermocapillary forces play a crucial role in the formation process. Analytic and numerical predictions show good agreement with the pillar spacings obtained in experiment. Simulations of the interface equation further determine the rate of pillar growth of importance to technological applications.Comment: 5 pages, 4 figure

The Effect of Truck Design on Pavement Performance

When work is done on some materials systems, their internal geometric states are altered in such a way that they have the potential to give back work when the force is removed and the system returns to its original configuration. This stored energy is called strain energy. Strain energy density (strain energy per unit volume) is a function of the Young\u27s modulus of elasticity and Poisson\u27s ratio and the nine strain (or stress) components; but it is independent of the coordinate system. Material properties are input into the Chevron N-layer computer program to calculate the strain components. Having calculated the strain energy density at a point, another quantity called work strain can be defined as the value of the strain corresponding to an uniaxial stress situation leading to the same strain energy density at the point. It can be used as the \u27\u27effective strain and is related to any single component of strain. Thus, pavement design systems based upon a single component of strain may be easily converted to a strain energy density basis. Configurations with loads distributed equally between the axles of an axle group were evaluated and damage factor relationships are reviewed. However, inspections of tandem axle suspensions on semitrailer trucks have shown that most tandem groups do not distribute the load equally to the axles. A theoretical investigation was made using pavement structures identical to those tested at the AASHO Road Test. The 1976 W-6 Table for Kentucky was used to obtain actual weight data. Preliminary analyses of tandem groups for 3S2 vehicles revealed a 40-percent increase in EAL over that calculated EAL assuming the total load on each tandem group had been uniformly distributed to the axles

Water-Induced Surface Failures on I 65, Hardin County, Kentucky

This report documents an investigation of water-related distress on portions of I 65 in Hardin County, Kentucky, on Muldraugh Hill. An open-graded surface placed on a full-depth asphaltic concrete pavement had shown areas of flushing and shallow shear failures in the outer lanes after one year of service. Cores were obtained from the outer lanes in areas exhibiting no problems to shear and flow failures. Core sites also were chosen across the lane to represent edge, wheel track, and between wheel track conditions. Visual inspection of the cores was made under normal lighting and an ultraviolet light and photographs were taken. Construction data and records indicated no abnormal construction problems. Results of laboratory density, extraction, and gradation tests coupled with nuclear density tests and visual inspection of the cores indicate water had caused the asphalt to be stripped from the aggregate. Soft particles in the dense-graded surface course below the open-graded course had deteriorated. The stripped asphalt and deteriorated soft particles had migrated toward the surface causing the pores to be filled in most locations. Where the asphalt/matrix was particularly weak, heavy truck tireloads had caused the material to move laterally over the adjacent stiffer material. Water is being held in the pores of the open-graded course and allowing the dense-graded surface course below to become saturated causing the asphalt to be stripped from the aggregate and softer particles to become deteriorated

Strain Energy Analysis of Pavement Designs for Heavy Trucks

The first portion of this paper summarizes classical concepts of work, or strain energy, as applied to the analysis of stresses, strains, and deflections under various vehicular load configurations on pavement systems. Controlling equations for strain energy density are presented. When considering strain energy density, strain energy, or work, all components of stresses or strains must be taken into account so that total internal behavior can be evaluated. Previously, pavement thickness design systems have been developed using only a single component of strain, typically at the bottom of the asphaltic concrete layer or at the top of the subgrade. Strain energy concepts permit modifications to thickness design systems to account for the net effect of all components of strains or stresses. The second portion of this paper illustrates the significance of detailed analyses. Effects of loads and load distributions on vehicles are summarized. One startling result shows the large increase in fatigue rate due to unequal distribution of loads between the two axles of a tandem group relative to the fatigue under an equal load distribution. A third part of this paper deals with pavement thickness designs for heavily loaded trucks exceeding legal load limits. The effects of those vehicles on interstate pavements are compared to the effects of more normally loaded vehicles

Pair Correlations, Short Range Order and Dispersive Excitations in the Quasi-Kagome Quantum Magnet Volborthite

We present spatial and dynamic information on the s=1/2 distorted kagome antiferromagnet volborthite, Cu3V2O7(OD)2.2D2O, obtained by polarized and inelastic neutron scattering. The instantaneous structure factor, S(Q), is dominated by nearest neighbor pair correlations, with short range order at wave vectors Q1=0.65(3) {\AA}^-1 and Q2=1.15(5) {\AA}^-1 emerging below 5 K. The excitation spectrum, S(Q,{\omega}), reveals two steep branches dispersing from Q1 and Q2, and a flat mode at {\omega}=5.0(2) meV. The results allow us to identify the cross-over at T*=1 K in 51V NMR and specific heat measurements as the build-up of correlations at Q_1. We compare our data to theoretical models proposed for volborthite, and demonstrate that the excitation spectrum can be explained by spin-wave-like excitations with anisotropic exchange parameters, as also suggested by recent local density calculations.Comment: Rewritten article resubmitted to Phys. Rev. Lett. 021

Modifications to Chevron N-Layer Computer Program

This report documents changes made to the Chevron N-layer computer program to: Include superposition principles. Calculate strain energy density (or work) at specified locations within the pavement structure. Analyze pavement response at specified radii from one circularly loaded area to permit comparison of analyses by the program as originally written with results incorporating superposition principles. Evaluate pavement response to any combination of loads on circular areas defined by XY coordinates on the surface. Loads and contact pressures are permitted to be different from one loaded area to another, but must be constant for any one loaded area. Simulate dynamic loads as the difference between the root mean squares of the maximum and minimum dynamic loads. This analysis is appropriate for constant vibratory testers such as Road Raters and Dynaflects. Moduli of asphaltic concrete must be adjusted for frequency effects

An experimental study of droplet-particle collisions

When spray drying a liquid slurry such as milk, collisions between droplets, partially dried particles and completely dry particles are important because coalescence, agglomeration and breakup events influence the size and morphology of the produced powder. When modelling such a spray drying process, it is therefore important to be able to predict the outcomes of individual binary collisions. Both binary dry particle collisions and binary droplet collisions have individually been thoroughly researched over the years due to their widespread occurrence. The importance of understanding binary particle-droplet collisions has been emphasized more recently. However, the number of available studies is limited and simulation studies usually focus on relatively high capillary number. A theory explaining the transition between different regimes is still lacking. The goal of this study is to provide an experimental data set at low capillary number. These results can be used to validate future theories and simulations. To produce and record particle-droplet collisions, an experimental setup that enables synchronized release of both a particle and a droplet was used. One single hanging droplet was released from above onto a particle that initially was held in place by vacuum suction. A high speed camera was synchronized with the setup, and recorded the collisions. Image files were then analysed in Matlab to find velocities and sizes of the particle and droplet before and after impact. The contrast of particle and droplet against the illuminated background was a key factor in succeeding with this. Different collision outcomes were identified as either agglomeration (merging), where the whole droplet would stick to the surface of the particle, or a stretching separation (breaking), where the droplet collides with the particle in an oblique position and stretches out until a part of the droplet detaches from the liquid sticking to the particle. The formation of satellite droplets, i.e. droplets with a radius significantly smaller than the leaving droplet, was also detected. The relation of these collision outcomes to impact conditions such as Weber number and impact parameter was reviewed and put into regime maps

Prevalence of sero-markers and non-invasive assessment of liver cirrhosis in patients with hepatitis B virus infection in Freetown, Sierra Leone: a cross-sectional study

BACKGROUND: Hepatitis B virus (HBV) is a major global health problem. Although sub-Saharan Africa has a high proportion of the global burden of HBV, the epidemiology and clinical features of HBV in this region are poorly characterized, and access to diagnostic and treatment services remain limited. METHODS: We conducted a retrospective study of HBV-infected children and adults of all age groups who were evaluated at public and private health facilities in Freetown, Sierra Leone between January 2017 and January 2019. We assessed their clinical presentation, HBV sero-markers, stages of liver disease, prevalence of cirrhosis by non-invasive tools, and the proportion of treatment eligible patients using the criteria recommended by the World Health Organization's 2015 treatment guidelines for HBV. Logistic regression was used to identify predictors of liver cirrhosis. RESULTS: 163 HBV patients included in the study, with mean age 32.6 years and 65.0% (106) being males. Most (84.0%) were asymptomatic at presentation. The majority (69.9%) were classified as having HBeAg-negative chronic infection (or inactive HBsAg carrier phase), 24.5% were in the HBeAg-negative immune active phase, 3.1% had HBeAg positive hepatitis, and 2.5% were HBsAg negative. The median Aspartate aminotransferase to Platelet Ratio (APRI) and Fibrosis-4 (FIB-4) scores were 0.37 and 0.80, respectively. The prevalence of cirrhosis was 7.6% and 6.2%, estimated by the APRI and FIB-4 scores, respectively. About 20.0% of patients were eligible for treatment with antiviral agents. Based on APRI scores, the presence of any symptom [adjusted odds ratio (aOR) 20.0, 95% confidence interval (CI) (4.1-85.9); p < 0.001], elevated direct bilirubin [aOR 12.1, 95% CI (1.9-63.0); p = 0.003], and elevated total bilirubin [aOR 16.1, 95% CI (3.2-80.8); p = 0.001] were independent predictors of cirrhosis. CONCLUSION: Although most patients with HBV infection were asymptomatic, the prevalence of liver cirrhosis and proportion of patients requiring antiviral treatment were substantial. This small study from a hyperendemic setting in Sierra Leone suggests that routine population-based screening may increase early detection and linkage of HBV patients to care before development of complications. Larger studies are needed to confirm our findings