Epidemic model on a network: analysis and applications to COVID-19

We analyze an epidemic model on a network consisting of susceptible-infected-recovered equations at the nodes coupled by diffusion using a graph Laplacian. We introduce an epidemic criterion and examine different vaccination/containment strategies: we prove that it is most effective to vaccinate a node of highest degree. The model is also useful to evaluate deconfinement scenarios and prevent a so-called second wave. The model has few parameters enabling fitting to the data and the essential ingredient of importation of infected; these features are particularly important for the current COVID-19 epidemic

Radiolysis and Thermolysis of Cytosine: Importance in Chemical Evolution

An important aspect of chemical evolution is the study of the stability of organic molecules with biological significance in primitive conditions, especially in the presence of constant energy sources. An example of sets of biologically important organic compounds is nitrogenous bases. The presence of these compounds in prebiotic environments is very important in forming more complex systems, such as nucleic acids, in which nitrogenous bases are an essential component. The aim of the present work is to study the stability of cytosine, a pyrimidine base, in high-radiation fields or at high temperature and to evaluate its recovery. Our results show that the cytosine (1x10-4 M aqueous solution, oxygen-free) decomposed completely at a dose of 22 kGy, and 25% recovery was obtained with a dose of 7.4 kGy. The analysis of irradiated samples was followed by HPLC, HPLC-mass spectrometry and UV-VIS spectroscopy. The main product in both thermolysis and radiolysis was uracil, formed via a deamination reaction. Uracil is another nitrogenous base with biological significance

Radiolysis of the Glycolaldehyde-Na+Montmor- illonite and Glycolaldehyde-Fe3+Montmorillonite Systems in Aqueous Suspension under Gamma Radiation Fields: Implications in Chemical Evolution

The stability and reactivity of organic molecules with biological and pre-biological significance in primitive conditions are of paramount importance in chemical evolution studies. Sugars are an essential component in biological systems for the different roles that they play in living beings. The objective of the present work is to study the gamma radiolysis of aqueous solutions of glycolaldehyde, the simplest sugar and aqueous suspensions of glycolaldehyde-Na+-montmorillonite and glycolaldehyde-Fe3+Montmorillonite. Our results indicate that the radiolysis of the aqueous solutions of glycolaldehyde (0.03M), oxygen free, mainly produce the linear dimer known as eritriol (122 g/mol) and a sugar-like compound with six carbon atoms (180 g/mol). The experiments with the clay suspensions show that clays can adsorb glycolaldehyde and protect it from gamma irradiation. Additionally, it was observed that depending on the cation present in the clay, the percentage and the product (monomer or cyclic dimer) adsorption was different. In the case of Fe3+ Montmorillonite, this clay catalyzed the decomposition of glycolaldehyde, forming small amounts non-identified products. The analysis of these systems was performed by ATR-FTIR, UV spectroscopy, liquid chromatography (UHPLC-UV), and HPLC coupled to a mass spectrometry

Study of L-Glutamic Acid in Solid State for its Possible Use as a Gamma Dosimeter at Different Temperatures (77, 195 and 295 K)

The experimental response of the dosimeter as a function of the irradiation temperature plays an important role, and this effect has consequences in the practical applications of dosimetry. In this work, L-glutamic acid (2-aminopentanedioic acid) is proposed to be a good response, easy to handle, and a cheap gamma dosimeter. For this purpose, polycrystalline samples were irradiated with gamma rays at 77, 195, and 295 K and doses in the kiloGray range (43–230 kGy). The potential use of the glutamic acid system as a chemical dosimeter is based on the formation of stable free radicals when the amino acid is exposed to ionizing radiation. The observed species in these experiments were attributed to deamination and decarboxylation reactions that were studied using electron spin resonance (ESR). The results indicate that the analysis generates a linear response as the irradiation dose increases in a reliable range for industrial and research purposes at three different temperatures

Study of Solid-State Radiolysis of Behenic, Fumaric, and Sebacic Acids for their Possible Use as Gamma Dosimeters Measured Via ATR-FT-IR Spectroscopy

The intensive use of ionizing radiation has promoted the constant investigation of adequate dosimetric systems in the measurement of doses applied in irradiated products. The objective of this work is to propose gamma dosimetric systems, using carboxylic acids in a solid state and measuring the change via infrared spectroscopy (carboxylic acid/ ATR-FT-IR1). We worked with three systems: (1) behenic acid/ATR-FT-IR, (2) sebacic acid/ATR-FT-IR, and (3) fumaric acid/ATR-FT-IR. The change in absorbance corresponding to the stretching vibration frequency of the carbonyl group to the absorbed dose (in the range of kGy) was measured. The results showed that the acid/ATR-FT-IR systems have a linear response with respect to the absorbed dose, for behenic acid/ATR-FT-IR from 0 to 122 kGy, for ATR-FT-IR sebacic acid from 0 to 61 kGy, and for fumaric acid/ATR-FT-IR from 0 to 34 kGy. The results indicated that the linear response of the absorbance dose in the three systems allows us to continue studying other variables to be able to propose them as chemical dosimeters

Spectrophotometric Study of Polymeric DyesGels After a Gamma Irradiation Process for its Possible Use as a Radiation Dosimeter

This work aims to evaluate a dosimetric system composed of green malachite supported in agarose. Previous work showed that solutions of green malachite irradiated at 1 to 40 kGy present a linear behavior. This system is a gel composed of green malachite (2.5×10–3 M), sodium benzoate (1%),and agarose (1%) that was exposed tovarious doses of gamma irradiation. The irradiated systems were measured with a UV-V is spectrophotometer at 619 nm. Experimental parameters (such as dose rate, doses, and temperature) were controlled and optimized for reproducible and reliable results. More studies are needed to propose a dosimeter in the system in the range of 1.8 to 4.0 kGy

Stated benefits from air quality improvement through urban afforestation in an arid city – A contingent valuation in Mexicali, Baja California, Mexico

Cities in drylands are expected to experience increasing challenges when it comes to air pollution. Currently, concentrations of particulate matter in these cities frequently reach dangerous levels. Urban afforestation represents an alternative to increase human health in arid cities via air-filtering and dry deposition. By simulating a non-existing market through a contingent valuation protocol, this study estimates the willingness to contribute monetarily to an urban afforestation scenario in Mexicali -an arid city located at the US-Mexico border. We estimate an average annual willingness to pay (WTP) of (2019) USD 88 per household. Variations in WTP are associated with the respondent's perception of air quality and the presence of respiratory symptoms in the respondent's household. The smallest WTP (USD 75) is reported by those perceiving poor air quality in their neighborhood and with no household members affected by respiratory symptoms. Respondents perceiving good air quality and with at least one household member facing respiratory symptoms report a WTP of USD 99. The highest WTP represents around 0.8 % of the annual household income. This WTP, when extrapolated to and aggregated over the total number of households in Mexicali, justifies the implementation of an urban afforestation program supplying 30 thousand tree seedlings annually

Gamma Dosimetry Using Some Dyes in Organic Solvents Solutions at 295 and 77 K

The aim of this work is to study the behavior under irradiation of different dyes (green malachite, methyl orange, red cresol, and bromothymol blue) in organic solvents (acetone and methanol) at different gamma doses and different temperatures to propose them as possible dosimeters for low-temperature applications. For this purpose, organic dissolutions were irradiated with gamma rays in the kiloGray (kGy) range at 77 and 295 K, and the color bleaching of the solutions was followed spectrophotometrically (UV-Vis range). The response curves at different temperatures show the linear range interval from 10 to 40 kGy with correlation coefficients of 0.999 and 0.998 for some systems. This is the main reason to continue carrying out studies that allow the proposal of these systems as chemical dosimeters

Programa de evaluación externa de la calidad en los servicios que brindan las unidades de auditoría interna de los laboratorios farmacéuticos del área metropolitana de San Salvador.

La unidad de auditoría interna en El Salvador cada vez tiene más importancia en las compañías, por el aporte en el logro de objetivos y metas de la empresa; por lo tanto, es necesario que: cumplan con el Marco Internacional para la Práctica Profesional (MIPP), la cual no es aplicada en su totalidad al no realizar evaluaciones externas de calidad, la cual es ejecutada por un grupo externo con experiencia en el área, esto se puede constatar en el desarrollo de la investigación, la problemática identificada ha sido que personas jurídicas (Firmas de auditoría) inscritas en el CVPCPA y ofrecen el servicio de “outsourcing” en auditoría interna, no poseen programas de evaluación externa de la calidad. En este sentido, el objetivo del trabajo es proporcionar programas de aseguramiento y mejora de la calidad, enfocados en la evaluación externa, que permita competencias del personal y oportunidades de trabajo a las personas jurídicas (Firmas de auditoría) inscritas en el CVPCPA, a su vez brinde a los laboratorios farmacéuticos confianza y mejora de la actividad de auditoría interna, garantizando o no, el cumplimiento del Marco Internacional para la Práctica Profesional (MIPP). Para el desarrollo de la investigación se utilizó el enfoque cuantitativo, mediante el uso del método hipotético deductivo, el cual fue abordado por medio de encuestas realizadas a los auditores de las personas jurídicas (Firmas de auditoría) inscritas en el CVPCPA y a los laboratorios farmacéuticos de los cuales se obtuvieron los elementos necesarios para concluir que: ii Las personas jurídicas (Firmas de auditoría) inscritas en el CVPCPA necesitan tener programas de evaluación externa de la calidad adecuados, que permita analizar las actividades ejecutadas por la unidad de auditoría interna de los laboratorios farmacéuticos. Por lo tanto, se recomienda que sea capacitado el personal de las firmas de auditoría que ofrecen el servicio de “outsourcing” de auditoría interna en la ejecución de la evaluación externa de la calidad. Así mismo, que la unidad de auditoría interna debe incluir en sus actividades el programa de aseguramiento y mejora de la calidad que permita evaluación externa