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16870 threads, 325775 comments (2 Viewing)
Views: 113, Comments: 21
Last comment 05/28/2022 by canadianslidewinder

Lithium Sulfur Batteries

05/25/2022 by Rixter
This looks promising... https://www.youtube.com/watch?v=ln5u-DETWS0 https://www.youtube.com/watch?v=H-AjRrGglCE
Views: 64, Comments: 3
Last comment 05/26/2022 by PWSlack

RoboRat vs RatDroid

05/24/2022 by HiTekRedNek
I recently read about a robot,shaped like a rat for exploring confined,small areas where access is not practical or impossible other wise. Over 20 ye...
Views: 130, Comments: 12
Last comment 05/25/2022 by SolarEagle
Views: 141, Comments: 11
Last comment 05/26/2022 by SolarEagle
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Commercial Space

2113 threads, 4308 comments (0 Viewing)
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CR4 Feedback

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Section Blogs

Challenge Questions

412 blog entries, 30332 comments (0 Viewing)

Beer Can Blueprints (May '22 Challenge Question)

What are the practical reasons to have concave and beveled bottoms on beer cans? (Okay, so it applies to soda pop cans too.) The image is of a flat-b...
Views: 798, Comments: 26
Last comment 05/23/2022 by Anonymous Poster

A Spicy, Open-Ended Design Solution (April '22 Challenge Question)

This month's question is a bit different. Rather than a single specific answer, or set of answers, this one challenges your critical thinking. You ha...
Views: 506, Comments: 14
Last comment 04/22/2022 by canadianslidewinder
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CR4 Welcome Wagon

7 blog entries, 20 comments (0 Viewing)

Be excellent to each other

In recent weeks we’ve talked about eliminating political discussions, reporting things to moderators and also rating threads and comments. If e...
Views: 187, Comments: 11
Last comment 01/09/2022 by phoenix911

Moderator Justice

This is CR4: Moderator justice The moderators and administrators of CR4 are employees of Globalspec, and [a small] part of our job is to keep CR4 run...
Views: 74, Comments: 0
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Other Blog Entries of Interest

Pesky Ellipse Circumference

10/04/2020 posted in Relativity and Cosmology
by Jorrie
When I first heard that there is no easy exact formula for the circumference of the standard ellipse, I found it hard to believe. I had already learne...
Views: 398, Comments: 8
Last comment 11/30/2020 by Haymaker

SpaceProperTime Diagrams and the Central Singularity

08/24/2020 posted in Relativity and Cosmology
by Jorrie
In my prior Blog post on the Einstein equivalence principle, I have not identified important values, like the mass of the black hole, real distances a...
Views: 287, Comments: 4
Last comment 08/25/2020 by Jorrie

SPT-Acceleration and the Equivalence Principle

08/17/2020 posted in Relativity and Cosmology
by Jorrie
One day after Alice's arrival at Deep-2, she and Dot sat down for the change of shift briefing - recall that Dot must soon return for Home leave. Whil...
Views: 170, Comments: 8
Last comment 08/18/2020 by Jorrie

Space-Propertime Structure and Acceleration II

08/11/2020 posted in Relativity and Cosmology
by Jorrie
This is a fanciful little scenario for 'flexing the muscles' of acceleration in space-propertime a little and so giving a better intuitive feel for th...
Views: 182, Comments: 8
Last comment 08/18/2020 by canadianslidewinder

Space-Propertime Structure and Acceleration

08/07/2020 posted in Relativity and Cosmology
by Jorrie
I have introduced the idea of Epstein Space-Propertime Diagrams (ESPD) in my previous Blog post. To refresh, here is the ESPD's structural relationshi...
Views: 225, Comments: 6
Last comment 08/08/2020 by Jorrie