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Spectroscopy
Published in C. R. Kitchin, Astrophysical Techniques, 2020
One of the first light instruments for the Extremely Large Telescope (ELT) will be High Angular Resolution Monolithic Optical and Near-Infrared Spectrograph (HARMONI). Its details are still under discussion, but it is clear that it will be one of the ELT’s prime workhorse instruments. It is expected to have its own adaptive optics system that will use one natural and six artificial guide stars and operate via the main telescope’s fourth mirror. HARMONI will be an IFU, possibly based upon image slicers, with four spectrographs, spectral resolutions between 3,500 and 20,000 and covering the 470-nm to 2.45-μm spectral region. Its field of view will range from 600 × 800 milliarcseconds to 6 × 9ʺ using array detectors with up to 32,000 pixels and it will be cooled to 140 K.
Kinematic Design and Applications of Flexures
Published in Paul Yoder, Daniel Vukobratovich, Opto-Mechanical Systems Design, 2017
Hardware described or referenced in this chapter ranges from simple opto-mechanical subassemblies to high-level systems. Application of the rules given here for properly constraining each DOF applies at all levels of complexity. Many examples of simple flexure mountings are given here. Additional examples are included elsewhere in this book. One complex example with many properly constrained parts is the proposed support structure for the primary mirror segments of the European Extremely Large Telescope (E-ELT) currently under development. With a 39.3 m (129 ft) aperture, this is expected to become the largest near-infrared telescope in the world. The main characteristic of this and all other instruments considered here is always the achievement of maximum performance and predictability with minimal weight.
Telescopes
Published in Daniel Malacara-Hernández, Brian J. Thompson, Fundamentals and Basic Optical Instruments, 2017
Marija Strojnik, Maureen S. Kirk
The multiple-mirror telescope represented a truly novel way of achieving large diameters: if one can combine six mirrors, why not 12, or 18 or even more: 36 in the case of Keck, and 127 for the extremely large telescope (ELT). Figure 11.37 compares the sizes of the primary mirrors of the Hubble, the Keck, and the ELT. The anticipated growth of the segmented mirrors represents an extension of the theorem of natural numbers: if you can build a two-segment primary mirror, then assume that you can build an N-segment mirror, and see if you can build an segment mirror. Of course you can, and you will, because the astronomical community wants to intercept photons from even fainter sources, and they just need to count them. This has been the design philosophy of the Keck telescope as well as the Spanish telescope in the Canaries [108]. An accurate calibration of the interaction matrix optimizes the performance of the adaptive optics system. The future European extremely large telescope is expected to exhibit a few thousand mirror modes. Meimon et al. [109] describe calibration strategy applicable to adaptive optics systems in a closed loop. They incorporate the slope-oriented Hadamard method to obtain 7-fold improvement (i.e., decrease) in the calibration time.
Improving fracture and moisture resistance of cold mix asphalt (CMA) using crumb rubber and cement
Published in Road Materials and Pavement Design, 2022
Dana Daneshvar, Arash Motamed, Reza Imaninasab
Due to the increased number of vehicles, the generation of End of Life Tyres (ELTs) has been substantially increased over the past years. The ELT disposal can cause several adverse impacts on the environment and human health. It has been shown that resistance to the action of microorganisms, environmental pollutions, increased risk of fire in landfills, emission of toxic gases, such as benzene and phenol, and the increasing costs of landfill operations are the disadvantages of landfilling (Mui et al., 2004). Grinding is an ELT treatment technology usually used to produce Crumb Rubber (CR) (Airey et al., 2003; Li et al., 2010). CR recovered from grinding can be mixed with asphalt binders to improve the rheological properties. The addition of CR to asphalt binder not only gives a sustainable solution to re-use the ELTs, but also improves the performance of asphalt mixtures, increases the service life, and reduces the maintenance cost. In this regard, previous studies have shown that CR modified asphalt mixtures indicating higher resistance to rutting, fatigue cracking, and low-temperature cracking (Behnood & Olek, 2017; Kim, 2001; Lee et al., 2008; Shu & Huang, 2014). Pettinari et al. (2013) reported that CR can also improve the fatigue resistance of the cold recycled mixtures. The efficiency of CR in enhancing the performance of asphalt mixtures highly depends on the modification method, amount of CR, and the type of aggregates and base binder (Heitzman, 1992; Liu et al., 2009). Regarding the modification method, there are generally two techniques to incorporate the CR, namely dry and wet processes (Roberts et al., 1989). In the dry process, CR is added into aggregates before mixing with binder. So, after mixing with binder, the CR particles become part of the mixture mastic and, this contributes to the flexibility of asphalt mixture (Cao, 2007; Presti, 2013). In the wet process, the CR is directly blended with binder to modify the properties of binder. The blending process is carried out at high temperatures (typically about 177–210°C) using a high shear mixer with high rotational speed (Fontes et al., 2010; Shu & Huang, 2014).