12 Jan, 4 tweets, 2 min read
1/
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?
2/
The position (p, q) of your sensor at each detection event is listed below, along with time of detection and bearing to target.
3/
Offered solution: target is at (452, 119) course 119 degrees speed 9.9

Actual target: (453,118) course 119 speed 10
4/
I think the biggest source of the slight discrepancy is imprecision of detection angles. Solution method described here:

• • •

Missing some Tweet in this thread? You can try to force a refresh

This Thread may be Removed Anytime!

Twitter may remove this content at anytime! Save it as PDF for later use!

# 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
15 Apr 20
1/
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?

2/
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
3/
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
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.*
1/
2/
Centralized quarantine (CQ) means infected people not needing hospitals stay in govt-run facilities where they are to some degree physically detained.
3/
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.
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…)
1/
@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.
3/
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…)