6/15/2023 0 Comments Ispectrum magazine![]() All three species used both deep and shallow torpor, often on the same night. We infrared imaged three hummingbird species that are known to use deep torpor, under natural temperature and light cycles, to test whether they were also capable of shallow torpor. Although the literature hints that some bird species (mousebirds and perhaps hummingbirds) can use both shallow and deep torpor, little empirical evidence of such an avian heterothermy spectrum within species exists. Deep torpor occurs in three avian orders, but the trade-offs of deep torpor in birds are unknown. However, deep torpor in mammals can increase predation risk (unless animals are in burrows or caves), inhibit immune function and result in sleep deprivation, so even for species that can enter deep torpor, facultative shallow torpor might help balance energy savings with these potential costs. arctic ground squirrels, hummingbirds) enter deep torpor, dropping their body temperature by 23–37☌, while others can only enter shallow torpor (e.g. Many endotherms use torpor, saving energy by a controlled reduction of their body temperature and metabolic rate. Unfortunately, this kind of model often fails to provide estimates that are accurate enough for a given application. To analyze more complex environments, numerous empirical models have been developed, such as the well-known P recommendations from the International Telecommunication Union–Radiocommunication Sector. However, due to insufficient computational capacity, this approach has been traditionally confined to problems involving relatively simple geometries, such as determining the electromagnetic field radiated by a dipole. Īrguably, spectrum cartography can be traced back to the application of Maxwell’s equations to characterize the propagation of radio waves across space. Radio maps are also useful for localization and tomography. Radio maps find a myriad of applications in wireless communications and networking, such as network planning, interference coordination and mitigation, power control, resource allocation, handoff management, multihop routing, dynamic spectrum access, and cognitive radio networking tasks see and and the references therein. A quick overview of the most representative types of radio maps is provided in Table 1. Spectrum cartography comprises a collection of techniques used to construct and maintain radio maps, which provide useful information on the radio-frequency (RF) landscape, such as the received signal power, interference power, power spectral density (PSD), electromagnetic absorption, and channel gain across a geographic area see, e.g.,, , and. ![]() To gain insight into this versatile toolkit, illustrative toy examples will also be presented. ![]() Starting from simple regression, the exposition gradually delves into more sophisticated algorithms, eventually touching upon state-of-the-art techniques. In this tutorial article, after presenting some representative applications of radio maps, the most prominent RME methods are discussed. Radio map estimation (RME) typically entails interpolative inference based on spatially distributed measurements. Radio maps characterize quantities of interest in radio communication environments, such as the received signal strength and channel attenuation, at every point of a geographical region.
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