Universal Behavior of Extreme Price Movements in Stock Markets

Many studies assume stock prices follow a random process known as geometric Brownian motion. Although approximately correct, this model fails to explain the frequent occurrence of extreme price movements, such as stock market crashes. Using a large collection of data from three different stock markets, we present evidence that a modification to the random model -- adding a slow, but significant, fluctuation to the standard deviation of the process -- accurately explains the probability of different-sized price changes, including the relative high frequency of extreme movements. Furthermore, we show that this process is similar across stocks so that their price fluctuations can be characterized by a single curve. Because the behavior of price fluctuations is rooted in the characteristics of volatility, we expect our results to bring increased interest to stochastic volatility models, and especially to those that can produce the properties of volatility reported here.Comment: 4 pages, 3 figure

Curvature(s) of a light wavefront in a weak gravitational field

The geometry of a light wavefront evolving from a flat wavefront under the action of weak gravity field in the 3-space associated to a post-Newtonian relativistic spacetime, is studied numerically by means of the ray tracing method.Comment: 3 pages, 1 fig, Talk given by JFPS at the 12th Marcel Grossmann conference (Paris, July, 2009), submitted to the Proceeding

Geometry of an accelerated rotating disk

We analyze the geometry of a rotating disk with a tangential acceleration in the framework of the Special Theory of Relativity, using the kinematic linear differential system that verifies the relative position vector of time-like curves in a Fermi reference. A numerical integration of these equations for a generic initial value problem is made up and the results are compared with those obtained in other works.Comment: 10 pages, LaTeX, 2 eps figs; typos corrected, added reference, minor changes; submitte

A comparative study of acid and alkaline aluminum extraction valorization procedure for aluminum saline slags

A management process for saline slags, one of the wastes from Secondary Aluminum Production, is proposed. The process begins with a grinding step, followed by washing with water, which removed the fluxing salts but provoking the hydrolysis of AlN, yielding Al(OH)3 and ammonia. Sieving of the solid generated an intermediate and a fine fraction. The first one was rich in metallic aluminum, and can also be returned to the Secondary Aluminum Production. The fine fraction was submitted to a extraction process in acid (HCl or HNO3) or alkaline (NaOH, KOH or CsOH) conditions, under reflux at 90 ºC, obtaining an Al(III) solution that can be used in the synthesis of aluminum-based solids. HCl (1-8 mol/L) and NaOH (1-4 mol/L) were used as reference solutions, HNO3, NaOH and KOH were used under specific conditions; the slag fraction:extraction solution solid:liquid ratio was also varied. The optimum extraction conditions were: extraction time 2 h, solid:liquid ratio 3:10, concentration 3 mol/L for the NaOH medium and 4 mol/L for the HCl medium. More than 30% of the aluminum present in the fraction smaller than 0.4 mm was recovered (the remaining aluminum was present as insoluble phases, corundum and spinel). Acid or basic media can be selected depending on the final use of Al(III) solutions, the basic medium leading to an Al(III) solution with a lower amount of impurities. The hazardousness of the solid obtained after the extraction process was greatly decreased, making possible the use of this solid residue in sectors such as construction.This work was supported by 'Memoria de D. Samuel Solórzano Barruso' Foundation (FS/11-2020). AJ thanks Universidad de Salamanca and Banco Santander for a predoctoral contract. AG is grateful for financial support from the Spanish Ministry of Science and Innovation (MCIN/AEI/10.13039/501100011033) through project PID2020-112656RB-C21. AG also thanks Santander Bank for funding via the Research Intensification Program

Edible packaging based on natural sources for food applications

16th IUFoST World Congress of Food Science and Technology: Addressing Global Food Security and Wellness through Food Science and Technology[Excerpt] Innovations constantly appear in food packaging, always aiming at creating a more efficient quality preservation system while improving foods’ attractiveness and marketability. The utilization of renewable sources for packaging materials, such as hydrocolloids from biological origin, is one of the main trends of the food packaging industry. Edible films/coatings have been considered as one of the potential technologies that can be used to increase the storability of foods and to improve the existent packaging technology, helping to ensure microbial safety and preservation of food from the influence of external factors. [...]info:eu-repo/semantics/publishedVersio

Development and characterization of galactomannan acetate nanoparticles

16th IUFoST World Congress of Food Science and Technology: Addressing Global Food Security and Wellness through Food Science and Technology[Excerpt] Nanoparticles from natural polysaccharides are a good alternative for synthetic compounds due to their biocompatibility, biodegradability, hydrophilicity and protective properties. Galactomannans are neutral, water-soluble polysaccharides highly used in food industry. They have potential for the preparation of nanoparticles that can be used as a carrier for functional compounds for food and pharmaceutical applications. The present work aimed at developing nanoparticles from guar gum through acetylation of the galactomannan and using the solvent diffusion method for nanoparticle formation. The obtained nanoparticles were characterized by means of dynamic light scattering (DLS) (size and polydispersivity), Fourier transform infrared (FTIR) and transmission electron microscopy (TEM). Guar gum was acetylated through solubilization in formamide at 54 ºC. Then pyridine and acetic anhydride were added and left under stirring for 48 h at 54 ºC. The obtained solution was precipitated and purified in water. After successive washings with water the precipitate was dried at 35 ºC during 48 h. The nanoparticles were obtained through the solvent diffusion method by solubilization of acetylated galactomannan solution in DMSO that was then dispersed in water. [...]info:eu-repo/semantics/publishedVersio

Groundwater pollution in quaternary aquifer of Vitoria - Gasteiz (Basque Country, Spain)

As a result of diverse changes in land use and in water-resource management in the high basin of the Zadorra River (Basque Country), an important loss of water resources and an intense contamination by nitrogen compounds has taken place. The purpose of this paper is to detail the land transformations that have taken place on the aquifer since the 1950s: increase of drainage network, change from dry to irrigated farming, and diversion of rivers at the aquifer unit inlet. Furthermore, we analyze the impact of these transformations on the hydrodynamics and water quality of this aquifer system