Science – shiqiv.com

How much of the terrestrial lands have been modified by human beings?

A recent study published on Global Change Biology revealed a far lower estimate of 5% than the previous 19%.

(a) Cumulative human modification (HMc) across global terrestrial lands | Source: Global Change Biology

Thirteen human factors in 6 categories are considered in calculation.

human settlement (population density and built‐up areas)
agriculture (cropland and livestock)
transportation (major roads, minor roads, two tracks, and railroads)
mining
energy production (oil wells and wind turbines)
electrical infrastructure (powerlines and nighttime lights)

Meanwhile, nearly 50% of the lands are considered with low human modification.

So there is a contrast of how little of the land (5%) we haven’t touched and how much of the land we haven barely explored (44%)

「Video of the Week」Higher Dimensions of Space

A very good educational discussion of hyperspace on World Science Festival 2010 and a brief of The Elegant Universe by Brian Greene (the book I am finishing).

Some Underlying Physics of 5G Network

[personal notes]

1. Friis Transmission Law
  ${\frac {P_{r}}{P_{t}}}=D_{t}D_{r}\left({\frac {\lambda }{4\pi d}}\right)^{2}$
2. frequency is inversely proportional to wavelength
  $\displaystyle v=f\lambda$
3. in the case of electromagnetic radiation, v is approximate 3×10⁸ m/s

In ITU standards,

Extremely high frequency (EHF) = 30 to 300 GHz in frequency = 10 to 1 mm in wavelength, so called millimeter-wave (mmW)

Ultra high frequency (UHF) = 300 MHz to 3 GHz in frequency = 1 to 0.1 m in wavelength

UHF is where our current mobile networks live on, with 4G mostly on 700 MHz, 1700-2100 MHz, 1900MHz and 2500-2700 MHz across the globe.

Under the Friis Transmission Law, higher frequency has much higher loss (attenuation) in free-space. For mmW, additional transmission losses occur when traveling through the atmosphere are absorbed by molecules of oxygen, water vapor and other gaseous atmospheric constituents.

Important absorption peaks occur at 24 GHz (for water vapor) and 60 GHz (for oxygen).

mmW attenuation | Source: T.S. Rappaport, NYU Wireless

As range of 5G signals are limited, small cells deployment, collaboration and integration will be essential. Current experiments found a 200-meter range doable.