Research group at Arizona State University claimed their developmental satellites “femtosats” (small CubeSats) could cost as little as US$3,000 to put in orbit. Computer Science

Research group at Arizona State University claimed their developmental satellites “femtosats” (small CubeSats) could cost as little as US$3,000 to put in orbit.
Problem in a reduction proof for undecidability of machines
A simulator written in JavaScript for the reversible instruction set Bob
MIT & Adobe Introduce Real Time AR Tool for Storytelling
Cracking the Real Time Security Chip checks on Retro Konami arcade pcb’s - feedback and thoughts welcome :)
Huawei’s First Commercial AI Chip Doubles the Training Performance of Nvidia’s Flagship GPU
Hey everyone, I’m thinking of making an app but I want to make sure I use all precautions to avoid a cyber attack, what are the main things I should look into to include in my app to increase the security of the users
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Research group at Arizona State University claimed their developmental satellites “femtosats” (small CubeSats) could cost as little as US$3,000 to put in orbit.

Posted: 23 Aug 2019 10:27 AM PDT

submitted by /u/Akkeri
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Problem in a reduction proof for undecidability of machines

Posted: 24 Aug 2019 12:24 AM PDT

The following content is quoted from Micheal Sipser's introduction to theory of computation. The bold text is where I am facing problem.

Theorem : ETM is undecidable; ETM ={⟨M⟩|M is a TM and L(M)=∅}.

PROOF IDEA: We follow the pattern adopted in Theorem 5.1. We assume that ETM is decidable and then show that ATM is decidable—a contradiction. Let R be a TM that decides ETM. We use R to construct TM S that decides ATM. How will S work when it receives input ⟨M, w⟩?

One idea is for S to run R on input ⟨M ⟩ and see whether it accepts. If it does, we know that L(M) is empty and therefore that M does not accept w. But if R rejects ⟨M ⟩, all we know is that L(M ) is not empty and therefore that M accepts some string—but we still do not know whether M accepts the particular string w. So we need to use a different idea.

Instead of running R on ⟨M ⟩, we run R on a modification of ⟨M ⟩. We modify⟨M⟩ to guarantee that M rejects all strings except w, but on input w it works as usual. Then we use R to determine whether the modified machine recognizes the empty language. The only string the machine can now accept is w, so its language will be nonempty iff it accepts w. If R accepts when it is fed a description of the modified machine, we know that the modified machine doesn't accept anything and that M doesn't accept w.

So first question is if R is fed the description of modified machine should not it accept w because we modified it to accept w but it says it does not accept anything and it does not accept w. and it is not mentioned what is done empty string from the description I can only understand that the modified machine accepts only w and not the empty string. I need clarification of this.

PROOF

Let's write the modified machine described in the proof idea using our standard notation. We call it M1.

M1 = "On input x:

If x ̸= w, reject.
If x=w, run M on input w and accept if M does."

This machine has the string w as part of its description. It conducts the test of whether x = w in the obvious way, by scanning the input and comparing it character by character with w to determine whether they are the same.

Putting all this together, we assume that TM R decides ETM and construct TMS that decides ATM as follows.

S = "On input ⟨M,w⟩, an encoding of a TM M and a string w:

Use the description of M and w to construct the TM M1 just
described.
Run R on input ⟨M1 ⟩.
If R accepts, reject ; if R rejects, accept .

Note that S must actually be able to compute a description of M1 from a description of M and w. It is able to do so because it only needs to add extra states to M that perform the x = w test.

If R were a decider for ETM, S would be a decider for ATM. A decider for ATM cannot exist, so we know that ETM must be undecidable.

Now the second question is from point 3 in the description S. But lets move to 2nd point first we are running R(decider for ETM) on M1 which means it will reject if x /= w and accept otherwise. Now to point 3 if R accepts we reject in S(decider for ATM) because it first is performing a check on x=w it passes that but we know ATM is undecidable so it must reject same for when it accepts.

Please let me know if there are missing points in my understanding of it and correct where I am wrong being a theory person I would like how you tackle this problem.

submitted by /u/sachal10
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A simulator written in JavaScript for the reversible instruction set Bob

Posted: 24 Aug 2019 03:19 AM PDT

For those who are interested:

http://brkmnd.com/pages/projects/Default.aspx?id=37

submitted by /u/brkmnd
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MIT & Adobe Introduce Real Time AR Tool for Storytelling

Posted: 23 Aug 2019 09:06 AM PDT

submitted by /u/Yuqing7
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Cracking the Real Time Security Chip checks on Retro Konami arcade pcb’s - feedback and thoughts welcome :)

Posted: 23 Aug 2019 05:50 AM PDT

So I've recently been working on removing real time clock security checks on the Konami M2 arcade platform. A lot of Konami hardware uses these chips, and generally it's to check against a security code on the CD / ROM chip programmed and installed on the pcb.

In the boot sequence, the hardware checks the disc code (in my project 636JAC02) on the cd, and it compares it to the 7K rom, which also holds 636JAC02.

It then checks the disc code against the data written to a volatile Real Time Clock chip. If all three match the pcb boots. If one or more do not match, it throws up a general hardware error.

The real time clock itself is not employed in the security check. It's just used for time unlocked secret characters / features. They just shoved some bits of data (byte swapped compared to the game disc and 7K rom) onto the RTC as a secondary security check.

You can spoof the discs in a hex editor to alter the security key and get games to boot on non-target pcb's (each game was married to its pcb) but I have a friend who's board arrived from japan with the security pcb missing entirely, hence my work.

I wanted to share my work to help others understand the process / get feedback from others. Any suggestions / feedback / etc would be super helpful. Below is a link to part one of my YT video on the subject. Seems the auto mod is touchy about vid links so just add in the .com manually :)

youtube. /watch?v=xpuLKpaIbeE

submitted by /u/chicagogamecollector
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Huawei’s First Commercial AI Chip Doubles the Training Performance of Nvidia’s Flagship GPU

Posted: 23 Aug 2019 11:39 AM PDT

submitted by /u/Yuqing7
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Hey everyone, I’m thinking of making an app but I want to make sure I use all precautions to avoid a cyber attack, what are the main things I should look into to include in my app to increase the security of the users

Posted: 23 Aug 2019 06:22 PM PDT

submitted by /u/swiftybrucman
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C++20 Is Feature Complete; Here’s What Changes Are Coming

Posted: 23 Aug 2019 10:24 AM PDT

submitted by /u/Akkeri
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Shared Machine Learning: An Alternative to Federated Learning?