When comparing grating performance curves, it is important to keep this in mind. In contrast, relative efficiency compares the energy diffracted into the desired order with that of a plane mirror coated with the same material as the grating. The absolute efficiency of a grating is the percentage of incident monochromatic radiation that is diffracted into the desired order. Grating efficiency is a function of groove shape, angle of incidence and the reflectance of the coating. The general grating equation is usually written as: nλ = d(sin i + sin i’) where n is the order of diffraction, is the diffracted wavelength, d is the grating constant (the distance between successive grooves), i is the angle of incidence measured from the normal and i’ is the angle of diffraction measured from the normal.įor a specific diffracted order (n) and angle of incidence (i), different wavelengths (λ) will have different diffraction angles (i’), separating polychromatic radiation incident on the grating into its constituent wavelengths. To learn more about our ruling and holographic mastering processes, click here. Ruled and holographic gratings differ in their optical characteristics and each type has advantages for specific applications. We are one of the few companies that produce both types of gratings in-house and has full replication facilities and expertise. Gratings produced from laser constructed interference patterns and a photolithographic process are known as interference or holographic gratings. Physically forming grooves into a reflective surface with a diamond mounted on a “ruling engine” produces ruled gratings. The way in which the grooves are formed separates gratings into two basic types, holographic and ruled. If the wavelength is much smaller than the groove spacing, the facets of the groove will act as mirrors and, again, no diffraction will take place. If the wavelength of the incident radiation is much larger than the groove spacing, diffraction will not occur. The distance between adjacent grooves and the angle the grooves form with respect to the substrate influence both the dispersion and efficiency of a grating. More research is needed to study how social media users discuss health through sharing images online, and how public health professionals can communicate effectively using image-sharing social media.A grating consists of a series of equally spaced parallel grooves formed in a reflective coating deposited on a suitable substrate. A few studies attempted to use image-based social media as intervention tools, but the results were mainly exploratory. Most observational studies investigated questions ranging from public perception of diseases or interventions (vaccination) and undesirable media exposure ("echo chamber," distorted body image, underage substance use, and pro-suicide messages) to information dissemination and online engagement (likes and comments). Public health-oriented research on Instagram, Pinterest, Tumblr, and Flickr is increasing. Other topics included chronic diseases, infectious diseases, surgery, injury prevention, pharmacovigilance, sexual and reproductive health, and adolescent psychology with functional magnetic resonance imaging. More than half of the included articles were related to mental health and substance abuse (n = 39, 59%). Of the 54 observational studies, 38 studied Instagram 12, Pinterest 7, Tumblr and 6, Flickr some studies investigated more than 1 platform. All 12 experimental studies used Instagram. Sixty-six research articles were included. Only public health-related, peer-reviewed research articles were included (excluding surveys of self-reported social media use). We searched EBSCOhost Academic Search Complete, PubMed, and Web of Science in January 2016, April 2017, and November 2017, with the following keywords: Pinterest, Instagram, Tumblr, or Flickr. No known systematic review exists that summarizes the existing research and its health implications. Image-based social media Instagram, Pinterest, Tumblr, and Flickr have become sources of health-related information and tools for health communication.
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