Methods and apparatus, including computer program products, implementing and using techniques for customizing a graphical function display. The optical system includes a refractive optical element which includes a solid-state material, a negative lens component and a positive lens component, respectively disposed on a front side relative to a pupil, the solid-state material meeting conditions of an Abbe number \u03bdd and of a partial dispersion ratio \u03b8gF as follows:\u22122. An estimated response of the MIMO channel is obtained, and an equivalent channel response is derived based on the estimated MIMO channel response and a response of a feed-forward filter of a decision feedback equalizer. Re-programmability of the PLD provides significant flexibility in providing features that can be parameterized based on the user’s needs andor associated design. 25 mm and less characterizing the first corner structure and the second corner structure, a first coupling region between the first exit region and a first surface region of a first photovoltaic device. If the battery power availability is below a predefined threshold, then one or more power-saving techniques can be triggered that increase an air time of the mobile device and provide savings of power consumption at different rates using a different level of clock rate.