Physics of Radiation Biology
Kedar N. Prasad in Handbook of RADIOBIOLOGY, 2020
Electrons are negatively charged particles and orbit the atomic nucleus in a precisely defined path, each path being characterized by its own unique energy level. Electrons are positioned in shells or energy levels that surround the nucleus. The first or K shell contains no more than 2 electrons, the second or L shell no more than 8 electrons, and the third or M shell no more than 18 electrons (Figure 3.2). The outermost electron shell of an atom, no matter which shell it is, never contains more than 8 electrons. Electrons in the outermost shell are termed valence electrons and determine to a large degree the chemical properties of an atom. An atom with an outer shell filled with electrons seldom reacts chemically. These atoms constitute elements known as the inert gases (helium, neon, argon, krypton, xenon, and radon).
Fluid Bed Processing
Dilip M. Parikh in Handbook of Pharmaceutical Granulation Technology, 2021
Kulling and Simon [18] reported the closed-loop system shown in Figure 10.34. The inert gas (generally nitrogen) used for fluidization circulates continuously. An adjustable volume of gas is diverted through the bypassed duct where solvent vapors are condensed, and solvent collected. The circulating gas passes through the heat exchanger to maintain the temperature necessary for the evaporation of the solvent from the product bed. During the agglomeration and subsequent drying process, the solvent load in the gas stream does vary. The bypass valve controls the flow of the gas to the heat exchanger and the condenser. By controlling the gas stream in this manner, the drying action is continued until the desired level of drying is reached. Even though the cost of the fluid bed processor with the solvent recovery is generally double the cost of a regular single pass fluid bed processor, such a system offers effective measures for both explosion hazard reduction and air pollution control.
Modeling Exposure
Samuel C. Morris in Cancer Risk Assessment, 2020
The risk of an exposure is dependent not only on the concentration of pollutants in the air, but also on conditions which determine how much of the pollutant actually is retained in the body. These are characteristics of the pollutant itself and of the exposed individual. The respiratory system has numerous self-protective systems built-in. The laws of physics also affect what fraction of the pollutant inhaled is retained and where in the system it is retained. Most of the air that is inhaled is immediately exhaled, along with many of the pollutants it contained. Reactive gases such as ozone or sulfur dioxide are more likely to be retained than inert gases. The more reactive they are, the higher up in the respiratory system they are likely to be trapped. Particles are more complex. In addition to diffusion to the sides of the respiratory tract, they are removed by impaction at bifurcations. Impaction depends on particle size and mass (combined into aerodynamic diameter, a measure of effective particle size). The respirability of particles is thus a function of particle size. To make matters more complex, hydroscopic particles (those which absorb water from the air) quickly grow as they enter the respiratory tract which is at close to 100% relative humidity.
Advances in encapsulating gonadotropin-releasing hormone agonists for controlled release: a review
Published in Journal of Microencapsulation, 2022
Nardana Bazybek, Yi Wei, Guanghui Ma
Spray drying is applied to produce microencapsulated or matrix-based drug delivery systems to obtain sustained drug formulation. This technology is a continuous process that transforms feedstock solutions into dried micro-sized particles by subjecting feed to a high-temperature and gaseous medium (Al-Khattawi et al.2018). According to Figure 5, spray drying consists of three main stages: atomisation, drying, and separation. Atomisation refers to converting a liquid stream into small fine particles by the appropriate device. In this stage, the prepared feedstock is delivered through a peristaltic pump to the atomiser chamber by a nozzle. Then, droplets are produced in the atomiser chamber by exposure to the interaction with a hot drying gas (higher than feed temperature) (Shi et al.2020). Atomised dispersion droplets are subjected to a hot gas stream in the second stage, which mainly refers to atmospheric air. In some cases, it is required to use inert gas to obtain the stability of particles. Process conditions such as inlet temperature, drying air temperature, and device geometry simultaneously influence the drying performance and efficiency. In the last stage, dried product particles are collected using a separation device as a cyclone (Cal and Sollohub 2010).
Mechanics of tablet formation: a comparative evaluation of percolation theory with classical concepts
Published in Pharmaceutical Development and Technology, 2019
Saurabh M. Mishra, Bhagwan D. Rohera
True density of the powder materials was determined using a gas pycnometer (AccuPyc® II 1340, Micromeritics Instruments Corp., Norcross, GA). The pycnometer allows nondestructive measurement of volume and density of powder and solid materials, and uses a gas displacement technique to determine the volume of the sample under test. An inert gas (helium) was used as the displacement medium. Pycnometer was calibrated with an iron sphere of known mass prior to each measurement. For the determination, a known weight of powder sample was transferred into an aluminum sample container of 3.5 cm3 volume, and helium gas was passed through the sample from the reservoir. The determinations were carried out at room temperature. The instrument automatically purges moisture and volatile materials from the powder sample and repeats the analysis until successive measurements yield consistent results. The determination of sample density was repeated for up to 10 cycles. The average reading of 10 cycles was recorded as the true density of the material.
Overview of prevention and management of acute bronchiolitis due to respiratory syncytial virus
Published in Expert Review of Anti-infective Therapy, 2018
Marwa Ghazaly, Simon Nadel
Helium is an inert gas, and its density is almost 15% that of air. Carbon dioxide (CO2) is more diffusible through helium than air. Helium inhalation results in maintenance of more laminar gas flow and decreases turbulence through narrowed airways, which subsequently lowers resistance to gas flow. Therefore, breathing heliox decreases airway resistance and reduces work of breathing [69,70]. Heliox has been shown to improve oxygenation in respiratory illness with moderate to severe airway obstruction, including in AVB [71]. A meta-analysis of four clinical trials (with 84 participants) using heliox, demonstrated improved respiratory distress scores in the first hour of its use in children with moderate to severe AVB. However, heliox inhalation did not affect need for intubation and mechanical ventilation and LOS in the pediatric intensive care unit [31,72]. The routine use of heliox is, therefore, not currently recommended.
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