Science and Technology links (May 22nd 2021)

  1. Most computer chips today in flagship phones and computers use a process based on a 5 nm or larger resolution. Finer resolutions usually translate into lower energy usage and lower heat production. Given that many of our systems are limited by heat or power, finer resolutions lead to higher performance. The large Taiwanese chip maker (TSMC) announced a breakthrough that might allow much finer resolutions (down to 1 nm). IBM recently reported a similar but less impressive breakthrough. It is unclear whether the American giant, Intel, is keeping up.
  2. Good science is reproducible. If other researchers follow whatever you describe in your research article, they should get the same results. That is, what you report should be an objective truth and not the side-effect of your beliefs or of plain luck. Unfornately, we rarely try to reproduce results. When we do, it is common to be unable to reproduce the results from a peer-reviewed research papers. The system is honor-based: we trust that people do their best to check their own results. What happens when mistakes happen? Over time, other researchers will find out. Unfortunately, reporting such failures is typically difficult. Nobody likes to make ennemies and the burden of the proof is always on you when you want to denounce other people’s research. It is so common that we have a name for the effect: the replication crisis. The reproduction crisis has attracted more and more attention because it is becoming an existential threat: if a system produces research that cannot be trusted, the whole institution might fall. We see the reproduction crisis in psychology, cancer research and machine learning. Researchers now report that unreproducible research can be cited 100 times more than reproducible research. It suggests that people who produce unreproducible research might have an advantage in their careers and that they might go up the ranks faster.
  3. Recent PCs and tablets store data on solid-state drives (SSDs) that can be remarkably fast. The latest Sony PlayStation has an SSD with a bandwidth exceeding 5 GB/s. Conventional (spinning) disks have lagged behind with a bandwidth of about 200 MB/s. However, conventional disks can be much larger. It seems, however, that conventional disks might be getting faster. The hard drive maker Seagate has been selling conventional disks that have a bandwidth of 500 MB/s.
  4. As you age, you accumulate cells that are dysfunctional and should otherwise die, they are called senescent cells. We are currently developing therapies to remove them. Martinez-Zamudio et al. report that a large fraction of some cells in the immune system of older human beings are senescent (e.g., 64%). Clearing these senescent cells could have a drastic effect. We shall soon know.
  5. There are 50 billion birds and 1.6 billion sparrows.
  6. Computer scientists train software neural networks (for artificial intelligence) using backpropagation. It seems that people believe that such a mechanism (backpropagation) is not likely to exist in biology. Furthermore, people seem to believe that in biological brain, learning is “local” (at the level of the synapse). Recently, researchers have shown that we can train software neural networks using another technique that is ‘biologically plausible’ called zero-divergence inference learning. The implicit assumption is that these software systems are thus a plausible model for biological brains. It is unclear to me whether that’s a valid scientific claim: is it falsifiable?
  7. Ancient Romans used lead for everything. It appears that Roman children suffered from lead poisoning and had a related high mortality rate.
  8. Knight et al. found strong evidence to support the hypothesis that vitamin D could help prevent breast cancer. Taking walks outside in the sun while not entirely covered provides your body with vitamin D.
  9. Mammal hearts do not regenerate very well. Hence, if your heart is damaged, it may never repair itself. It appears that some specific stem cells can survive when grafted to living hearts and induce regeneration.
  10. Persistent short sleep duration (6 hours or less) is associated with a 30% increased dementia risk. (Note that this finding does not imply that people sleeping a lot are in good health. It also does not imply that you are sick if you are sleeping little.)
  11. Researchers have rejuvenated the blood cells of old mice using a form of vitamin B3.
  12. There are 65 animal species that can laugh.
  13. Between the years 1300 and 1400, the area near Greenland became relatively free from ice, as it was effectively exporting its ice to subartic regions. It seems to match the beginning of the Little Ice Age, a time when, at least in Europe, cold temperatures prevailed.

Published by

Daniel Lemire

A computer science professor at the University of Quebec (TELUQ).

4 thoughts on “Science and Technology links (May 22nd 2021)”

  1. Re: claim 1: Actually, Dennard scaling stopped working circa 2006 and reducing feature sizes no longer reduces power consumption. We are now well into the era of power-constrained (rather than transistor-constrained) silicon design.

    It had a good 30-year run (1970s to 2000s), but it’s very much stopped now.

    The main problem is subthreshold leakage. Smaller transistors have thinner gate regions (smaller gate regions switch faster, a major benefit!), and quantum tunneling depends exponentially on the barrier thickness, even in a nominally impassible “off” transistor.

    Modern ICs try to strike a balance between switching current and leakage current, but it’s not easy.

    (The other problem is tolerances. As feature sizes shrink, manufacturing variation becomes proportionally larger, making everything more difficult.)

    1. I do not think I invoked Dennard scaling. High resolution processes have usually translated into more speed and reduced power usage. If you want to argue against that statement, you have to argue that from process to process, a vendor such as TSMC has not, usually, reduced the power usage (for a given processing speed).

      1. If you want to argue against that statement, you have to argue that from process to process, a vendor such as TSMC has not, usually, reduced the power usage (for a given processing speed).

        And that is exactly my claim. This is documented all over the place, e.g. What’s Next for Moore’s Law? For Intel, III+V = 10nm QWFETs
        or Power Challenges At 10nm And Below. (See also the link in the former to the coverage of the IEDM 2005 conference where the imminent demise of Dennard scaling was discussed in detail.)

        More specifically, the statement “Finer resolutions usually translate into lower energy usage and lower heat production.” implies a causal connection, which hasn’t been true for a long time.

        Rather, contemporary process engineers have to find a separate way to reduce power consumption lest their super-small transistors be rendered useless.

        The most obvious one in recent years has been FinFETs. And yes, FinFETs are normally sold in a bundle with geometries below a certain size in the same way that caches are included with processors above a certain clock speed, because it would be pointless otherwise.

        But that’s not because of the finer resolution; it’s more “in spite of”.

        As a crude software analogy, we all know perfectly well that the correlation between MHz and performance has been broken for some time.

        In the same way, smaller transistors haven’t caused lower power for quite a few years.

        As the articles linked above describe, these days power dissipation per active transistor has plateaued, and designers wishing to use more transistors have to find ways to keep the addition “dark”, i.e. non-switching. It’s straightforward to clock-gate unused cache banks, but other logic is trickier.

        1. > As a crude software analogy, we all know perfectly well that the correlation between MHz and performance has been broken for some time.

          I would still write that higher clock frequencies usually translate into higher performance.

          > And that is exactly my claim.

          Let us be precise. Your claim is "from process to process, a vendor such as TSMC has not, usually, reduced the power usage"? Are you sure you want to stand by that claim?

          You keep citing Dennard scaling but it is not a term that I seem to have ever used on this blog. At least, a keyword search does not find anything: https://lemire.me/blog/?s=Dennard

          I have used it in comments at least once, however. In 2018, I wrote… "An idea like Dennard scaling runs its course. Then something else comes along." https://lemire.me/blog/2018/07/21/science-and-technology-links-july-21st-2018/

          I searched for what I might have written in Dennard scaling over the years using Google. I submit to you that it is not a term that I tend to use. Note that I have been blogging weekly for almost 20 years. I write a lot.

          > But that’s not because of the finer resolution; it’s more “in spite of”.

          The adoption of finer resolution processors usually translate into better energy efficiency (normalized by computational power). It is simply a long-running trend.

          My post does not claim a causal link and it certainly does not invoke Dennard scaling (back in 2018 I alluded to the fact that it had run its course in a comment to another blog post). The phrase is finer resolutions usually translate into lower energy usage and lower heat production. That's not the wording I would have used if I meant to imply a causal relationship.

          To disprove my statement, you have to plot power efficiency over time, process by process, and show that it is not improving. But, of course, it is improving.

          Moore's law was not based on a "causal relationship" and yet it held for 30+ years.

          I would say that Americans tend to be overweight. There is no causality between the fact that one is American and being overweight, but there is an association. Simply put, if you ask me who weight more, and I am only told that A is Japanese and B is American, I will vote B any day. But there are underweight Americans and obese Japaneses.

          So it goes with processors… finer and finer processes tend to bring about power efficiency gains.

          Maybe you thought that I was invoking Dennard scaling… but the evidence is strong that I have been aware for quite some time that it is not a factor.

          We can reasonably discuss whether my implication will hold. Do you want to place a bet regarding the power efficiency of the next TSMC process? I bet that it will be at least 10% more power efficient.

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