Particles and Radiation
Rob Appleby, Graeme Burt, James Clarke, Hywel Owen in The Science and Technology of Particle Accelerators, 2020
For example, water has a refractive index of about 1.33 for visible wavelengths. Hence the Čerenkov angle is . Notice that Čerenkov radiation is emitted when any charge is moving through a material with , but we will only see that radiation if the material itself is transparent to it. Also, the Čerenkov radiation is emitted at 41° at any azimuth around the direction of the charge – the radiation is emitted as a cone. Slower-moving particles () give rise to a radiation cone which is narrower, and obviously the minimum velocity where Čerenkov radiation is produced is when , in other words when . In water, charged particles have to move faster than to generate Čerenkov radiation (Fig 6.30). Note that we haven't said what kind of charged particle can do this – any charge can generate Čerenkov radiation. However, usually it's electrons that we talk about since they are the most common situation.
Lasers in Medicine: Healing with Light
Suzanne Amador Kane, Boris A. Gelman in Introduction to Physics in Modern Medicine, 2020
When a beam of white light is passed through a glass prism, the result is a spectrum of light consisting of rays of different colors, each refracted by slightly different angles as they pass through the prism (Figure 3.6). This experiment has two interesting lessons. First, it shows that what humans experience as white light consists of light with a range of visible wavelengths. It's useful to appreciate that the glass prism separates white light into different color rays because the speed of light in glass is different for different wavelengths. As a result, the refractive index of the glass and the angle of refraction are slightly different for different wavelengths of light (see Equation 2.2). Rainbows result from a similar phenomenon when sunlight refracts and reflects from rain drops; crystal ornaments also produce rainbow-like effects from a similar mechanism. More generally, passing light through a prism allows us to determine its composition in terms of intensity for each range of wavelength, a quantity called its spectrum.
Bioengineering Aids to Reproductive Medicine
Sujoy K. Guba in Bioengineering in Reproductive Medicine, 2020
A single optical fiber consists of a central core cylinder of a transparent material usually glass, but could be plastics, having a refractive index σ1 covered with a closely fitting concentric hollow tube known as the “cladding”, also made of glass or plastic but having a different refractive index σ2 (Figure 3.23). The refractive index of the core material is higher than that of the cladding. Recalling elementary high school physics that when a light ray traveling in a medium of high refractive index strikes an interface with a material of lower refractive index, the ray can take three possible paths. If the angle of incidence (the angle between the direction of the ray and the normal to the interface) is low the light ray will escape into the low refractive index material. If the angle of incidence is high, the ray will be subject to ‘total internal reflection’ and will traverse back into the high refractive index material. At a critical angle of incidence (the angle equal to inverse sine of the ratio of the refractive index of the core medium to that of the cladding medium), the ray will neither escape nor travel back into the original material but will travel along a path just bordering the interface. Optical fibers function with the high angle of incidence as in the diagram (Figure 3.23) where at the point a the angle i being greater than the critical angle the ray is reflected back into the core. Similar reflections occur at B and C and so on till the ray emerges from the other end of the fiber.
Towards defining reference materials for measuring extracellular vesicle refractive index, epitope abundance, size and concentration
Published in Journal of Extracellular Vesicles, 2020
Joshua A. Welsh, Edwin van der Pol, Britta A. Bettin, David R. F. Carter, An Hendrix, Metka Lenassi, Marc-André Langlois, Alicia Llorente, Arthur S. van de Nes, Rienk Nieuwland, Vera Tang, Lili Wang, Kenneth W. Witwer, Jennifer C. Jones
The refractive index contrast between a particle of a certain material and its surrounding environment determines how much light is scattered from it [19]. The refractive index has no effect on measurements from non-optical techniques such as RPS [25]. For optical techniques that detect light scatter (e.g. flow cytometry, NTA, DLS, SP-IRIS), the refractive index strongly influences the particle measurements in the detectability of the particle or derivation of the particle diameter [19,39]. The refractive index is therefore an important metric to be provided with a reference material if it is intended for use with optical analysis techniques. Current literature suggests that while the refractive index of EVs is lower than reference materials such as silica, it is variable, Figure 5 [22,23,34,40]. Indeed, the effective refractive index of EVs will never be a single number due to an EV being a core-shell model, where the ratio of the shell (membrane) to the core (cytosolic portion) increases as EV size decreases. Smaller EVs will therefore have larger effective refractive indicies than larger EVs, such that refractive index cannot be reported with a single metric [22,23]. The term effective refractive index refers to a solid spherical particle with a given refractive index that scatters the same amount of light towards the detector as a similar-sized EV.
Alternatives to titanium dioxide in tablet coating
Published in Pharmaceutical Development and Technology, 2021
Juliana Radtke, Raphael Wiedey, Peter Kleinebudde
The particle size distribution of the pigments was determined by laser diffraction (Mastersizer 3000, Malvern Instruments, Malvern, UK). For this purpose, all samples were dispersed in water and measured three times using the wet-dispersion unit. The concentration of sample in water was selected in such a way that an optimal laser obscuration of 2 − 6% was guaranteed. Any agglomerates of particles were deagglomerated by ultrasound prior to each measurement. Using the corresponding software, the particle size distribution was determined from the data based on the Mie theory and given as volume distributions. The refractive index was adjusted depending on the material. For ZnO a refractive index of 2.0034 and for TiO2 of 2.493 was applied (Bodurov et al. 2016). Since the ready-to-use mixtures (APP117 and APP123) contained i.a. dibasic calcium phosphate, the refractive index of dicalcium phosphate (1.55) was applied for the respective measurements. The x10 quantile and the x50 quantile from the obtained distribution curves were used to describe the particle size. Determination was challenging for the ready-to-use mixture, since they contained further excipients like polymers and stabilizers. All other excipients except the pigments were however soluble and therefore expected not to interfere with the particle size determination. This was especially the case, since the sample was strongly diluted with water before measurement.
Lipo-PEG nano-ocular formulation successfully encapsulates hydrophilic fluconazole and traverses corneal and non-corneal path to reach posterior eye segment
Published in Journal of Drug Targeting, 2021
Shilpa Kakkar, Mandeep Singh, Sankunny Mohan Karuppayil, Jayant S. Raut, Fabrizio Giansanti, Laura Papucci, Nicola Schiavone, T. C. Nag, Nan Gao, Fu-Shin X. Yu, Mohhammad Ramzan, Indu Pal Kaur
SLNs were characterised for morphology using transmission electron microscopy ((TEM), Hitachi, Japan). Particle size (DelsaTM Nano C, Beckman Coulter, Brea, CA), drug assay/total drug content (TDC), entrapment efficiency (EE), and zeta potential of developed SLNs was also determined. Further physicochemical characterisation in terms of Fourier transform infra-red spectrometry ((FTIR), Perkin Elmer, Waltham, MA), differential scanning calorimetry ((DSC); TA Instruments, New Castle, DE), X-ray diffraction ((XRD), PANalytical, EA Almelo, Netherlands) and nuclear magnetic resonance ((NMR), Bruker, Fällanden, Switzerland), spectroscopy was also done. FTIR and XRD studies were conducted on lyophilised samples. pH, osmolarity, and refractive index ((RI) of the FCZ-SLNs was also determined as a measure of ocular comfort. RI was calculated using the formula n = c/v; where n is the refractive index of the medium, c is the velocity of light in vacuum and v is the velocity of light in the medium. Details of characterisation studies are included in the Supplementary data.
Related Knowledge Centers
- Refraction
- Snell'S Law
- Angle of Incidence
- Reflectance
- Total Internal Reflection
- Fresnel Equations
- Brewster'S Angle
- Chromatic Aberration
- Absorption
- X-Ray