Coming to grips with the nature of asynchronicity can prove very demandingfor conference and forum participants.All new online learners and e-moderatorshave some problems with it during their training (or if you allow them to workuntrained directly with participants).'There is no quick and easy way around thisproblem. They really do need to experience it for themselves. For instance,participants ‘post’ contributions to one conference then immediately readmessages from others, or vice versa.A participant might read all his or her unreadmessages in several conferences and then post several responses and perhaps postsome topics to start a new theme. In any conference, this reading and postingof messages by a number of individuals can make the sequencing difficult tofollow.All the messages are available for any participant (or researcher) to view online,so the sequencing of messages, when viewed after an e-tivity is completed, looksrather more ordered than during the build-up. Yet trying to understand themafterwards is rather like following the moves of a chess or bridge game after itis over. When participants start using e-tivities, this apparent confusion causes awide range of responses. The twists of time and complexity can elicit quiteuncomfortable, confused reactions from participants and severe anxiety in a few.Although many people are now familiar with email, they are not used to thecomplexity of online conferences, bulletin boards or forums. I suggest that goodstructure, pacing and clear expectations of participants should be provided, notonly for the scaffolding process as a whole but for each e-tivity. In addition, thee-moderator, or his or her delegate, should summarize after 10 or 20 messages.

An absolute location can be confidently calculated only when four (or more) distance values are available.

G. Rizzi and M. L. Ruggiero, editors, Relativity in Rotating Frames, p. 167.Kluwer, Amsterdan, 2004,

J.-F. Pascual-S ́anchez, L. Flor ́ıa, A. San Miguel, and F. Vicente, editors, Reference Framesand Gravitomagnetism, p. 53. World Scientific, Singapore, 2001

current GNSS: GPS and GLONASS. These systems are based on a Newtonian modelwhich is corrected numerically by important “relativistic effects”. This model uses the ECIand ECEF “Newtonian” reference frames, respectively for time reference and navigation

et us define location systems as the physical realizations of some coordinate systems.Location systems are of two different types: reference systems and positioning systems.The first ones are 4-dimensional reference systems which allow one observer, consideredat the origin, to assign four coordinates to the events of his neighborhood by means of atransmission of information. Due to the finite speed of light this assignment is intrinsicallyretarded with a time delay. The second one are 4-dimensional positioning systems (as usedin the SYPOR) which allow to every event of a given domain to know its proper coordinateswithout delay or in an immediate or instantaneous way.In Relativity, a (retarded) reference system can be constructed starting from an (immedi-ate) positioning system (it is sufficient that each event sends its coordinates to the observerat the origin) but not the other way around. In contrast, in Newtonian theory, 3-dimensionalreference and positioning systems are interchangeable and as the velocity of transmission ofinformation, the speed of light, is supposed to be infinite, the Newtonian reference systemsare not retarded but immediate.

LocationManager can provide a GPS location (lat,long) every second. Meanwhile, TelephonyManager gives the cellID=(mmc,mcc,lac,cid) the radio is currently camping on. A cellID database[1], allows to know the (lat,long) of each CellID. What is left is to draw the itinerary (in red) and, for each second, a cellID-color-coded connection to the cell.

in June, 2017, a French oil tanker, the Atria, sailed across the Mediterranean, through the Bosporus strait, and into the Black Sea. As the ship approached the Russian city of Novorossiysk, the captain, Gurvan Le Meur, noticed that the ship’s navigation system appeared to have lost its G.P.S. signal. The signal soon returned, but the position it gave was way off. The Atria was apparently some forty kilometres inland, shipwrecked at the airport in Gelendzhik, a Russian resort town.

How GPS Works

If the space doctor’s ideas were wrong, your phone wouldn’t be able to tell where it was.