Bizarre. Objectionable. My alma mater continues to have a completely different tradition, 40 years later. They have extremely well equipped labs, and the undergrads use them at any time for any project, including personal projects.
On a sunny day (Sat, 10 Aug 2019 06:52:59 -0700) it happened John Larkin wrote in :
Never heard of Cadfael, but did watch Catweazel in the seventies.
Have to think of his way of seeing things a lot...
Don't read into it too deeply. JL is not so talented at analysis, and forgets not to project his capability onto others.
The better lesson would be to work to your strengths, whatever they are; if they are analytic, then work on that. If not, work on faster methods of failing.
Note this traditional phrasing is as much derogatory as it is celebratory. Indeed, some problems provably do not have closed analytical solutions, so one of your better bets is simply cranking out attempts and picking the better results. Thus, failing often.
Which, again, is no excuse to check ones' brain at the computer. Problems can always be done smarter. Compare, say: the Leibniz formula for pi (the alternating harmonic series, which sums to pi/4), which converges extremely slowly; versus, the observation that the partial sums of that series alternate around the final value, so, wouldn't it be great if we could stick together pairs of terms with a properly tuned weighing factor and get much closer to the true result in far fewer steps? Applying the Newton convergence transformation gives a stupendous efficiency improvement (thousands of terms for a few digits vs. about as many digits as terms evaluated).
Is it better to run LTSpice for several hours, or sit with pad and pen for several hours then check the result in ten minutes of simulation? If the result is equivalent, it doesn't much matter for engineering purposes which one did it. Limiting yourself to just one approach is the real problem.
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/
I made the not-unreasonable assumption that your text formatting woes are due to a backwards, outdated system.
Linux has had hundreds of vulnerabilities over the years; you seem to take offense at that, which is strange?
I mean, the first step towards security is acknowledging you have vulnerabilities. The next step is securing them. You can't secure that which you are in denial about.
Which in turn implies that you aren't actually interested in the security of your machine, hence the strangeness.
Windows, excuse me? Where did that come in?
Oh, you must think I'm some sort of "fanboy" attacking your "camp" and so you must rush to its defense, spouting off every concievable deflection while continuing to ignore faults in your own system like being able to use punctuation in a random filename?
Strange. Well, this part isn't strange at all, it's the same tribalism that's tearing the world apart right now, really. More sad than strange. :-\
Ah, okay. So hopefully you've got most of these patched:
Waaait... 2.6? From 2011? But current version is 5.2.8 (stable)?! Then more specific I guess would be this,
Not that all of those appear to be critical RCE exploits, or are necessarily in modules that you use regularly. I have no idea. But I mean, it's not zero, which is all the point I'm after.
I must be misunderstanding something about Linux versioning or updating; surely it would be strange for someone to be questioning my (so far unstated) security practices, when they use a platform that hasn't been updated in the better part of a decade?
And, like, it's entirely plausible that you've been watching those, and patching your own kernel (and applications) locally. That would be cool. But a big burden, and a big distraction from getting any work done.
"Recompiling the kernel" seems to have always been a frequent refrain from the Linux community, which seems...bewildering to me? Do they expect average users to know how to do that? :(
Yeah, some crazy stuff going on these days. Not to mention the still present, and eminently hackable, Intel Management Engine hypervisor.
Good thing AMD doesn't have a Platform Security Proces--oh.
Uh?...
What?
You again seem to be willing me into a side of a conflict I have no care for, or stake in. I don't appreciate it.
Presumably Huwei will have "instrumentation" suitable for the Communist Party of China's purposes. Probably not active monitoring, but a fairly secure backdoor seems likely; the sort of thing our dear western leaders like to keep pushing. They may have /some/ sense about it, like a unique serial-numbered key per device, stored across isolated servers. I would expect typical services to be general unlock, pushing hidden apps / updates allowing targetted monitoring, etc.
This would be, I think, rather plausible and rather less conspiracy-theoretic.
Better them than us; but things would be so much nicer if We Could All Just Get Along(R). I guess we'll have to wait until Russia mass-pwns China's citizens to say "toldyaso" to them, and to our own leaders who keep pushing the same.
An interesting thing, as security goes: for all their problems, Apple has been quite staunch in their rejection of such softening measures. Indeed the gov't was so frustrated they even sued about it (and lost). It's not often you see such a visible and explicit confirmation like that.
The NSA is certainly getting their tentacles on everything they can. All the more reason to better review code, patch vulnerabilities as soon as they are found, and keep systems updated. Use crypto early and often, and responsibly.
For the record -- my desktop reports "AMD Phenom(tm) II X6 1055T Processor"
2.8GHz, and runs a 64-bit OS that is supported (for now..) and up to date. So, not particularly new (about as old as yours, actually, and I think both predating AMD's PSP?). I don't care for specsmanship, I don't run anything that would benefit from more, and my graphics card mostly handles whatever is left to do. And for that matter, the newest games I've played, haven't even been 3D, what a waste it seems. Ah well.Incidentally, *this* client (XP, OE6) is LAN attached only, and basically just kept around for news only. Attackable definitely, but a limited surface.
Tim
-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/
I don't :)
Your other points with which I wholeheartedly agree...
On a sunny day (Sat, 10 Aug 2019 12:55:55 -0500) it happened "Tim Williams" wrote in :
Na, I was not looking for a fight, thought you were. I have been running Linux since 1998 or so (Soft Landing Systems Linux it was called, found it on some CD that came with a magazine, and it replaced my win3.1 running on DRDOS with trumpet winsock. Before that internet we had Viditel here, more bulletin board oriented been 'online' since the eighties.
As I ran Free agent newsreader on that win 3.1 and there was no look alike Usenet newsreader for Linux, I wrote NewsFleX (this one:
So and also wrote most other apps that run here, except the web browser, that is a moving target and a life long work I have other interests. On top of that I am and always have been : root panteltje12: ~ # whoami root
Ran my own servers back then until that became to much work now website is at godaddy. And godaddy has leased servers close to here in the Netherlands, so I am basically local with that website. Anyways tell me about the web, asked Hacktick to hack my servers, they tried, I watched and they failed.
So, those were wilder years and lots of things were hacked.. Having Linux and gcc was and still is cool.
But I have no illusions about security, WiF was hacked here so all is wired now.
I tried (because of somebody advertising it here) win what was it? Xp ? once and it was removed really quick, new laptop came with some win version too, replaced it with Ubuntu the same day, now 4 different versions of Linux in different partitions on it. But this is my every day PC and very very hard to get into from the outside. Of course you should always use brain when using the browser... A very large part of the embedded world is running flavors of Linux, there are even satellites running it. Talk about reliability. ~ # uptime 20:48:39 up 79 days, 8:47, 15 users, load average: 2.35, 3.27, 3.78 Last reboot was 79 days ago, had to change some power cables? do not remember, For the rest I do not care who runs what, I wrote several OSes myself, some multitasker too. TCP stack for PIC, I can write what I want anytime in almost any language, except snake language 'python', NOTHING in all those years that I wrote has been hacked,. The hacked WiFi was a cheap Chinese security camera,, So, to make it easier for NSA I always explain my plans here, like the invasion of the US tomorrow (? or was it later) etc etc, and where I buy the plutonium and all that. You gotta help those guys, else they die of boredom.
As you probably noticed I have not much to say about the subject, so I will leave it at this, Reply at your own risk, that goes for using closed source software too, also from ratmond.
In fairness most undergrads don't design things. But if anyone wants to understand electronics at that age, they shoulda been designing things for years. Badly sometimes, how else does one learn.
NT
Was Apple's public stand for real, or was it showmanship when they complied behind closed doors? We'll probably never know.
NT
Well, the place was pretty fuddy-duddy. Most of the EEs went into power.
-- John Larkin Highland Technology, Inc trk jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Math is universal. College is just a friendly place to learn some of it Forgotten or not, math is omnipresent.
Not many people are talented at producing closed-form solutions to nonlinear system response. Most interesting electronic systems are nonlinear. What's a boy to do?
One big field where instinct+simulation usually (but not always) fails is filter design. Things can get crazy and diverge fast.
I have managed up to 5th order, mostly luck. I've done some nice one-side-absorptive lowpass filters by fiddling in Spice. The criterion for absorbing cable reflections was fuzzy, what looks good.
"Modern filter design" is computer based anyhow. That's where the tables in the books come from.
-- John Larkin Highland Technology, Inc trk jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Oh, we'll know. This kind of thing is a very temporary secret, at best.
Cisco sales (and stock) plummeted when their shipped products were found to have (official US government) tampering, and Apple's iPhone sales are too important to risk, so the public stand is probably also the private one.
Cisco's recent packaging is tamper-evident and more secure against counterfeiting than most currency. It's a SERIOUS concern that Apple and even Huawei must recognize, publicly and privately.
point taken :)
NT
"Very deep. You should send that in to the Readers' Digest--they have a page for people like you." --Ford Prefect
;)
Cheers
Phil Hobbs
If your schematic is really complete, then I think that the laws apply usefully, at least until the point where radiation is efficient. I am assuming here that current through parasitic capacitances is counted just as much as if it were a current flowing through a terminal of an intentional capacitor. If, in your schematic and arithmetic, you leave out things like the inductance and self-capacitance of wires, (and in difficult cases, even the distributed capacitance at different points along the inductance of wires), then of course the result of applying Kirchoff's laws to the (incomplete) schematic won't predict the behaviour of the actual construction. I suspect that radiation could also be modelled in a way that allows Kirchoff's laws to be applied but that the resulting schematic would be too complicated.
In making spice models for leadframes and bondwires, it makes a significant difference whether or not one includes the self-capacitance of the conductors (in addition to the mutual capacitances). Fastcap can extract all of these. You can apportion the capacitances to different points along the inductances of the conductors (extracted with FastHenry). The resulting model is very useful when simulating packaged chips, and of course the simulator at least attempts to satisfy Kirchoff's laws.
Nope. Transmission lines at the schematic level are non-local, i.e. you can't write a system of ODEs to describe a circuit with transmission lines or significant radiation. Kirchhoff's laws are derived from Maxwell's equations in the limit of low frequency (or alternatively, of small size for a fixed frequency).
And if you have to model the circuit "in a way that allows Kirchhoff's laws to be applied", you've implicitly admitted that they don't apply to the actual circuit.
Don't get me wrong--K's equations are useful and all, but they have limits. Being a physicist, I fully recognize the usefulness of sleazy approximations, but you have to remember that that's what they are, or you'll get snookered.
Yeah, a lot of times you can patch up approximations by hand like that--in my business one of the major examples is scalar optics, where you treat the EM field as though it had only one component. Polarization gets put in by hand once the calculation is done. Not the absolute cleanest procedure conceptually, but it works great for almost everything.
Another example is geometric optics, where you keep going back and forth between plane waves and rays, i.e. between infinitely broad wavefronts and infinitely narrow ones. When a ray encounters a curved dielectric surface, you assume that it bounced off the tangent plane at the point of incidence. That gives you the surface normal. Then you switch to the plane wave picture and apply Snell's law and the Fresnel formulae to get the direction and amplitude of the refracted ray. Both Snell and Fresnel depend on the wave picture, specifically phase matching at the boundary (Snell) and continuity of tangential E and perpendicular D (Fresnel). The derivation of Snell's law requires translational invariance, i.e. it only works on a flat boundary.
So to have well-founded confidence in our tools, we have to know where they break down and how to patch them up.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net https://hobbs-eo.com
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Analysis.pdf?dl=1
aHmm Phil, to put this in my own words... and please correct me if I'm wrong .. or I'm only part right. I think a limitation of K's laws is that they treat V and I as instantaneously the same everywhere.
George H. (every theory is an approximation at some level)
Everywhere on a given circuit node or loop, right. Anything with transmission-line behaviour can't be modelled as an ODE--the fields inside the T-line can be modelled with PDEs (Maxwell), but circuits are all ODEs. The T-line has invisible internal state, so its circuit behaviour is nonlocal.
Antennas have voltage nodes and antinodes on the same wire, so that K's voltage law doesn't hold, and they have current nodes and antinodes as well, so neither does the current law.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net https://hobbs-eo.com
I would say that that a wire on a schematic is not a valid representation of a transmission line, and if necessary I would approximate a transmission line as a ladder of (ideally infinitely) many series inductors and shunt capacitors. Of course very many components are required for this to be reasonably accurate.
At frequencies where the number of required components is excessive, I would then say that a schematic is not a good way to describe the physical system.
If by actual circuit we mean the physical object, then really I only expect Maxwell's equations to describe it, and I'm not very good at solving those. In a completely general sense I'm not even sure how one would try to apply Kirchoff's laws to an arbitrary three dimensional piece of electronics.
Agreed.
I guess I might have a rather unusual idea of what a schematic is, and this might be what causes me to take issue with what you said. To me, a schematic ought to be something that, when simulated (by some ideal simulator!), applying Kirchoff's laws, Ohm's law, i=C.dv/dt and so on, would sufficiently accurately predict the behavoiur of the real system.
To me, if the predictions are wrong, then I blame the schematic as being an inaccurate representation of the system, rather than blaming the equations used to simulate the behaviour of the schematic. Perhaps my philosophy on this topic comes from having had the job of making a schematic (sometimes pulling in netlists from field solvers) in order to simulate my design as implemented in a physical product. There was an expectation that I would use a circuit simulator provided to me, that did try to apply Kirchoff's laws (though not perfectly in the case of KCL). I did at least have the luxury that the physical dimensions of the system were a tiny fraction of a wavelength.
Yes, I agree in that, for example, if the build documentation schematic showed e.g., a resistor and a MOSFET, the simulation schematic should show the resistor's inductance or capacitance, as needed, and the MOSFET's Ciss, gm, and other aspects. But things get more painful when the part is say a high-performance op-amp, and you don't know what's in the manufacturer's model.
--
Thanks,
- Win
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