Fluctuations, Phase Separation and Wetting Films near Liquid-Gas Critical Point

Gravity on Earth limits the study of the properties of pure fluids near critical point because they become stratified under their own weight. Near the critical point, all thermodynamic properties either diverge or converge and the heating and cooling cause instabilities of the convective flow as a consequence of the expansibility divergence. In order to study boiling, fluctuation and phase separation processes near the critical point of pure fluids without the influence of the Earth\u27s gravity, a number of experiments were performed in the weightlessness of Mir space station. The experimental setup called ALICE II instrument was designed to suppress sedimentation and buoyancy-driven flow. Another set of experiments were carried out on Earth using a carefully density matched system of deuterated methanolcycloxexane to observe critical fluctuations directly. The set of experiments performed on board of Mir space station studied boiling and wetting film dynamics during evaporation near the critical point of two pure fluids (sulfur hexafluoride and carbon dioxide) using a defocused grid method. The specially designed cell containing the pure fluid was heated and, as a result, a low contrast line appeared on the wetting film that corresponded to a sharp change in the thickness of the film. A large mechanical response was observed in response to the cell heating and we present quantitative results about the receding contact lines. It is found that the vapor recoil force is responsible for the receding contact line. Local density fluctuations were observed by illuminating a cylindrical cell filled with the pure fluid near its liquid- gas critical point and recorded using a microscope and a video recorder. Microscopic fluctuations were analyzed both in sulfur hexafluoride and in a binary mixture of methanol cyclohexane. Using image processing techniques, we were able to estimate the properties of the fluid from the recorded images showing fluctuations of the transmitted and scattered light. We found that the histogram of an image can be fitted to a Gaussian relationship and by determining its width we were able to estimate the position of the critical point. The characteristic length of the fluctuations corresponding to the maximum of the radial average of the power spectrum was also estimated. The power law growth for the early stage of the phase separation was determined for two different temperature quenches in pure fluid and these results are in agreement with other experimental results and computational simulations

Investigation of Iron Oxide Nanocolloidal Suspension Diffusion Using a Direct Imaging Method

We performed a set of experiments using a direct imaging method to investigate the diffusion process of iron oxide, Fe2O3, nanoparticles. We studied concentration fluctuations that move against the concentration gradient and induce disturbances in the interface between the iron oxide suspension and water in the sample cell. Using this imaging method in combination with the differential dynamic algorithm for image processing, we are able to extract information about the power, size, and lifetime of the fluctuations. We performed this experiment both in the presence and in the absence of a 4.2 mT magnetic field. We find that the power and size of the fluctuations diminish in the presence of a magnetic field, as indicated by the change in slope of the structure factor from approximately -4 to -3, for q \u3c qc. Furthermore, we find that after the removal of the magnetic field, their power and size are still damped beneath those we observed during free diffusion, indicating that the nanoparticles are at least still slightly magnetized. From the lifetime of the fluctuations, we determined the diffusion coefficients of the nanosuspension in each environment

Bounds for Haralick features in synthetic images with sinusoidal gradients

Introduction: The gray-level co-occurrence matrix (GLCM) reduces the dimension of an image to a square matrix determined by the number of gray-level intensities present in that image. Since GLCM only measures the co-occurrence frequency of pairs of gray levels at a given distance from each other, it also stores information regarding the gradients of gray-level intensities in the original image.Methods: The GLCM is a second-order statical method of encoding image information and dimensionality reduction. Image features are scalars that reduce GLCM dimensionality and allow fast texture classification. We used Haralick features to extract information regarding image gradients based on the GLCM.Results: We demonstrate that a gradient of k gray levels per pixel in an image generates GLCM entries on the kth parallel line to the main diagonal. We find that, for synthetic sinusoidal periodic gradients with different wavelengths, the number of gray levels due to intensity quantization follows a power law that also transpires in some Haralick features. We estimate bounds for four of the most often used Haralick features: energy, contrast, correlation, and entropy. We find good agreement between our analytically predicted values of Haralick features and the numerical results from synthetic images of sinusoidal periodic gradients.Discussion: This study opens the possibility of deriving bounds for Haralick features for targeted textures and provides a better selection mechanism for optimal features in texture analysis applications

The Effect of Confinement on Fe2O3 Nanoparticles in Free Diffusion and with a Horizontal Magnetic Field

We investigated the magnitude of the confinement effect\u27s influence on the free diffusion of Iron Oxide Fe2O3 in pure water contained in cells of different volumes and also that of an applied magnetic field. A shadowgraph apparatus consisting of a super luminous diode (SLD) source, a CCD camera, and achromatic lenses was used to record and analyze the changing indices of refraction due to the presence of concentration-driven fluctuations as the solution diffuses. Extracted frames from this recording were processed through a Differential Dynamic Algorithm (DDA) that determined the dynamics of the process, such as the structure function. The results generated by the DDA was further analyzed to determine how the amplitude of concentration fluctuations change over time and how long those fluctuations are present, revealing a dependency of the dynamics on the size of the cell containing the solution

Impact of COVID-19 on Cryptocurrency Markets

The pandemic has caused enormous economic costs by affecting banks, governments and financial markets. In this context, the main purpose of this paper is to show that cryptocurrencies have become one of the most traded financial assets in the last decade. The overall objective pursued in the paper was the major effect on the global economy and financial markets that the COVID-19 Pandemic had and which was the first real global shock since the first cryptocurrency was launched in 2009 until now. Natural disasters and pandemics are a source of contagion in global financial markets and an emerging line of research. Financial contagion can be the result of both financial and non-financial events, but in both cases, assessments require defining a timeframe

Studying Near-Critical and Super-Critical Fluids in Reduced Gravity

Critical and supercritical fluids have a variety of applications, from use as machine lubricants in high pressure or high temperature environments to the manufacturing of materials such as aerogel. The optical properties of fluids undergo rapid changes near the critical point resulting in a rapid increase in turbidity known as critical opalescence. These optical changes can be used to probe the universality of critical behavior. As a fluid approaches the critical point, the compressibility rapidly increases. In a gravitational field, this increase in compressibility leads to near-critical fluids stratifying by phase and density, making it difficult to observe the optical properties of the fluid. Therefore it becomes necessary to study critical fluids in a reduced gravity environment. The HYdrogen Levitation DEvice (HYLDE) apparatus at CEA-Grenoble was used to study cells filled with oxygen and hydrogen suspended in a magnetic field as they were gradually decreased from the critical temperature (Tc). Using shadowgraph methods, we analyzed intensity map data to determine the light transmission and turbidity of critical and near critical hydrogen and oxygen. Turbidity measurements were made for a hydrogen filled cell at light wavelengths of 465.2 nm, 519.4 nm, and 669.4 nm. The turbidity of the oxygen filled cell was measured at 400 nm, 450 nm, 500 nm, and 650 nm

Tax Pressure on People's Incomes

The tax system is an essential part of any country's economic structure as it provides the government with a significant source of revenue and plays a crucial role in economic policymaking. In Romania, a nation with a complex tax system and evolving economic conditions, understanding the effects of the tax burden on the population is essential for assessing the fairness, efficiency and sustainability of public finance policies. The overall objective of the paper is to highlight that in recent years the issue of fiscal pressure on the population has received significant attention worldwide. As governments strive to maintain sustainable economic growth, there is a growing need to assess the impact of tax policies on individuals. The purpose of this work is to delve into the multifaceted nature of the tax burden, examine its implications for the population and propose policy perspectives to address the challenges it raises

Molecular Analysis of Echovirus 13 Isolates and Aseptic Meningitis, Spain

Echovirus 13 (EV13), considered rare, was reported worldwide in 2000, mostly related to aseptic meningitis outbreaks. In Spain, 135 EV13 isolates were identified. The genetic relationships between 64 representative strains from Spain and other reported isolates from the United States, Germany, Italy, Japan, and Sweden were described by analyzing the partial sequence of the major capsid protein (VP1) gene. The strains from Spain were clearly identified as EV13 (79.5% similarity with the EV13 reference strain) and were grouped phylogenetically into two different clusters (by origination on either the Iberian Peninsula or Canary Islands). Isolates from Germany from 2000 clustered with the Canary Islands group. The isolates from other countries obtained before 2000 were genetically distant. Changes in EV13 coding sequence involved several differences in the C-terminal extreme of the VP1 protein. Part of the neutralizing antigenic site III has been described in this genome region in poliovirus and swine vesicular disease virus