SONAR problem
Your UUV on patrol has detected a target four times as shown. Assuming that that this is one target travelling at constant course and speed, what is its course and latest detected position?
The position (p, q) of your sensor at each detection event is listed below, along with time of detection and bearing to target.
Offered solution: target is at (452, 119) course 119 degrees speed 9.9

Actual target: (453,118) course 119 speed 10
I think the biggest source of the slight discrepancy is imprecision of detection angles. Solution method described here:

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More from @benbenchia

11 Jan
(1/5) Some fairly straightforward math for deducing position, course and speed of a sonar target
(2/5) assumptions
(3/5) the key is to switch to Cartesian coordinates ASAP
Read 8 tweets
15 Apr 20
A question have been asking myself: When infections hit multiple family members (e.g. as a result of home quarantine of mild cases) what are the chances of orphaning any children?

For any infected person (incl. undiagnosed/mild), the probability of this doubly tragic outcome is:

Cohort IFR x cohort IFR x (probability of transmission)

some guesses using IFR for older folks
a) 0.5% x 0.5% x 60% = 15 per million
b) 1% x 1% x 80% = 80 per million
For a clinically confirmed case, the formula changes to:

Your CFR x partner's IFR x (probability of transmission before isolation)

a) 2% x 0.5% x 40% = 40 per million
b) 2.5% x 1% x 50% = 125 per million
Read 7 tweets
10 Apr 20
A survey of CENTRALIZED QUARANTINE (CQ) practices, or lack thereof

Background: Wuhan first tried home quarantine, part of standard epi procedure, but found that these ‘mild’ patients were
*infecting their families.*
Centralized quarantine (CQ) means infected people not needing hospitals stay in govt-run facilities where they are to some degree physically detained.
Singapore at first neglected, but has now adopted centralized quarantine (CQ.)

Because their 2nd wave of imported cases had a direct 2x or so multiplier effect in home quarantine. Image
Read 39 tweets
11 Dec 19
This March 2, 2019, image is the last published on @38North of the Sohae engine test stand without its post-Hanoi white cladding.
(source: 38north.org/2019/03/sohae0…)
@38north 2/
By March 6, everything had been closed up. Unless this thing has been torn up in the last 9 months without anyone noticing, the structure remains unchanged. Barring this, I assert that this stand could not have mounted a solid motor vertically.
Sorry, that’s @38NorthNK .

No further construction at the test stand has been reported from March.

However, there was an addition of what looks like office/lab space at the horizontal assembly facility, begun before January, roofed over May 2019. (38north.org/2019/05/sohae0…)
Read 8 tweets

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