> Take a look at the structure of something like CMOS and you’ll see why running transistors in anything other than “on” or “off” is definitely not energy efficient. In fact, the transitions are where the energy usage largely goes. We try to get through that transition period as rapidly as possible because minimal current flows when the transistors reach the on or off state.
Sounds like you might be thinking of power electronic circuits rather than CMOS. In a CMOS logic circuit, current does not flow from Vdd to ground as long as either the p-type or the n-type transistor is fully switched off. The circuit under discussion was operated in subthreshold mode, in which one transistor in a complementary pair is partially switched on and the other is fully switched off. So it still only uses power during transitions, and the energy consumed in each transition is lower than in the normal mode because less voltage is switched at the transistor gate.
> In a CMOS logic circuit, current does not flow from Vdd to ground as long as either the p-type or the n-type transistor is fully switched off.
Right, but how do you get the transistor fully switched off? Think about what happens during the time when it’s transitioning between on and off.
You can run the transistors from the previous stage in a different part of the curve, but that’s not an isolated effect. Everything that impacts switching speed and reduces the current flowing to turn the next gate on or off will also impact power consumption.
There might be some theoretical optimization where the transistors are driven differently, but at what cost of extra silicon and how delicate is the balance between squeezing a little more efficiency and operating too close to the point where minor manufacturing changes can become outsized problems?
The main issue is that when objects spin really, really fast, they tend to explode due to centrifugal force.
The tensile stress on a spinning round, homogeneous object is p * r^2 * w^2, where p is density, r is radius, and w is angular velocity. Using your numbers for a steel cylinder with density 8 g/cm^3 gives a tensile stress of (8 g/cm^3) * (5 mm)^2 * (2pi*1 MHz)^2 = about 8 TPa which vastly exceeds the tensile strength of steel or any other known material. Using cows connected by ropes would be even worse because the enormous centrifugal force would be borne by only a small rope.
That makes sense. With (strong) steel maxxing out at around 1Gpa, that's 4 orders of magnitude less. The rotation frequency gets squared, so... 10Khz? Huh: "The fastest rotation achievable by standard motors is of the order of 10 kHz". (How does a "standard motor" achieve 10 KHz without ripping apart, then? I don't think many standard motors are 5mm or smaller.)
Thinking about this makes me imagine a potter's wheel for shaping a ductile metal. It spins really fast, but you can only reshape in the outwards direction, and the resistance goes up dramatically towards the center. Oh, and if anything flakes off, you're dead. But before you die, you could probably make some pretty artwork.
I’m not an expert, but I don’t believe there are that many motors that spin at 600k RPM (= 10kHz), and definitely no large ones. That is absurdly fast. Modern turbochargers are some of the fastest-spinning off-the-shelf things your average person can buy, and they normally top out below 200k RPM (and only the smallest/lightest turbines can spin at 200k RPM). If there does exist a 500k+ RPM electric motor, I would be surprised if it was larger than a few mm.
You're ignoring the units of G. The gravitational constant has units N * m^2 / kg^2 = m^3 / (kg * s^2). That contains a length unit raised to the third power, which exactly balances the factor of 8 that you identified.
Landauer's limit assumes that computation uses a thermodynamically irreversible process and erases bits of information. This is not necessarily true for all useful computers [0]. So theoretically speaking, it's not impossible to create an adiabatic microprocessor. Skepticism is definitely warranted though.
To prove that it's possible to buy ads targeted on microphone audio. If this kind of targeting was really as widely available as the article implies, a journalist would be able to do it fairly easily and write an article about it.
But how would you know how the targeting was done? You place an ad and it gets a lot of clicks because it was targeted accurately (for example by using microphone recordings). You look into the dashboard and see a high click rate. What’s your story now?
In my experience, there are a lot of applications that are "trivial" enough that PID works fine. I'm reasonably comfortable with state space modeling for systems with more variables. But
OK, I'll bite - always open to picking up something new. What resources would you suggest for someone who wants to learn more about nonlinear controls?
Without knowing any specifics I would say the most universally useful tool to have in your nonlinear controls belt is Lyapunov control design and its extensions (if you're familiar with Lyapunov equations in linear systems that's where the connection starts). It leads to useful methods that are applicable to many systems, and allows you to handle some particularly tricky situations. Wikipedia's articles on these topics are surprisingly decent:
https://en.wikipedia.org/wiki/Control-Lyapunov_functionhttps://en.wikipedia.org/wiki/Backstepping
as well as Stanford's lecture notes:
https://web.stanford.edu/class/ee363/lectures/lyap.pdf
Check out Robust Nonlinear Control Design by Freeman and Kokotovic for more on this.
Compared to linear control theory, nonlinear controls is much more fractured and domain-specific. No concept is as widely applicable as ones from linear controls. Khalil's Nonlinear Systems book is generally considered a top reference, but it does start to get into the PhD-level stuff and I don't recommend it to a non-specialist unless you are really into this stuff. I can give more specific recommendations if you have a particular industry or application in mind.
Nuclear energy is hardly the only power source that has made an entire city uninhabitable. The Banqiao dam failure flooded 30 cities and affected over 10 million people.
https://en.m.wikipedia.org/wiki/1975_Banqiao_Dam_failure
And we're not even considering the effects of global warming here. Sure, nuclear has risks, but our civilization needs energy and nuclear has proven to be one of the least risky ways to produce it.
The most frequently discussed perovskite absorbers for solar cells are methylammonium lead trihalides, which are (at least partially) organic compounds.
