Science and Technology links (March 28th 2020)

    1. In a laboratory, we know how to turn any of our cells into youthful stem cells using something called the Yamanaka. If you expose cells to such factors for a short time, they appear to remain functional specialized cells but become more youthful. Researchers demonstrated this theory using cartilage cells from elderly patients suffering from osteoarthritis. They also rejuvenated muscle cells. It now remains to do the same in live human beings.
    2. It has been widely reported that artificial intelligence, and specifically deep learning, can match or surpass clinicians in medical imaging tasks. Unfortunately, it appears that this is far from demonstrated with the necessary rigor:

      Few prospective deep learning studies and randomised trials exist in medical imaging. Most non-randomised trials are not prospective, are at high risk of bias, and deviate from existing reporting standards. Data and code availability are lacking in most studies, and human comparator groups are often small.

    3. Apple released its latest tablet (the iPad Pro) with an integrated LiDAR that can map accurately your environment at up to 5 meters of distance. A LiDAR is basically a laser-radar. It was famously used by NASA to map the lunar surface in the 1970s but it was a technology out of reach to all of us twenty years ago: reserved for military and highly specialized applications.
    4. Japan and Korea have more than 13 hospital beds per 1000 people; Spain, Italy, and the U.S. have about 3 beds per 1000 people.
    5. Due to a worldwide pandemic, we are running the largest distance-learning experiment in history. Countless teachers worldwide are teaching online for the first time.
    6. Modern disks (such as a USB drive) might be lighter when they are filled with data than when they are empty.
    7. Our smartphones will soon move from 4G networks to 5G networks. The latter are much faster. However, they cause the phones to consume 20% more energy according to some report.
    8. A few decades ago, most of us had computers with a single processor. Over time we acquired processors with two processor cores, each core acting as a processor. Then we got four cores with some cores able to act as if they are made of two or four “logical” processors. The next gaming consoles (e.g., the PS5) will have main CPUs with eight processor cores. It is not difficult to find servers that have well over a hundred logical processors. Yet it appears that Windows was limited to at most 64 logical processors, possibly because the architects of Windows never imagined that we would soon reach this limit.

Daniel Lemire, "Science and Technology links (March 28th 2020)," in Daniel Lemire's blog, March 28, 2020.

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Daniel Lemire

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

5 thoughts on “Science and Technology links (March 28th 2020)”

  1. I will believe deep learning algos performance when they demonstrate true generalization. Train them on one dataset and test on another with the same label and same semantics. See if the algorithm does as well on images from a different CT machine, for example.

  2. Re 8: Windows is not limited by 64 processors for over 10 years. You might be interested in watching the following link, in which the person who made the patch discusses how this was done:

    (The grouping of processors to groups of 64 was mainly done for API & app compatibility reasons — apps that “declare” themselves as capable of handling more certainly can get there.)

  3. The news about thumb drives is doubly wrong.

    The author is correct that, by convention, a charged floating MOSFET gate represents a binary 0, while a discharged one represents a binary 1.

    However, flash memory is erased to the all-ones state. This is because discharging gates can only be done in large blocks (in the oldest UV EEPROMs, it required an external ionizing radiation source), but charging the gate can be done to selected bits.

    So unused flash memory is kept in the discharged-gate state in order to be able to accept newly written data as quickly as possible.

    The second error is that all of that does not affect the total number of electrons in the flash memory at all. The flash chip has zero net charge; any extra electrons in the floating gates are screened by missing electrons in the surrounding conductive structures, particularly the MOSFET channel. (Those missing electrons are the “field effect” in “field effect transistor” which are detected as part of the read process.)

    So the mass of an individual electron is simply irrelevant; there is no net change to the number of electrons in the flash chip.

    Now, is there any mass difference? Yes, but from a totally different source.

    The separation of charges created by charging the floating gates stores potential energy. The electrons in the floating gates want to bind with the holes in the channel, but are prevented by the gate insulation. If you know the gate capacitance and the voltage, you can compute this as E = CV^2/2.

    That potential energy (the reduction in the binding energy of the chip) turns out to have mass, by E = mc^2. (Lower-case c is the speed of light; upper-case is capacitance.)

    So take the total number of bits on the flash memory (include all overhead and ECC bits, generally at least 16 extra per 512 bytes, but not spare sectors), assume half (N/2) are programmed, and work the numbers. m = NCV^2/2c^2.

    (Most modern thumb drives use 4 or 8 voltage levels per bit to store 2 or 3 bits per transistor, so you have to sum over all the possible voltage levels.)

    1. That’s a fantastic comment.

      Note that in the link I wrote “might have” and I am happy that I did. I should have thought right away that the total number of electrons in the disk could not change, since I have never heard of disks as being charged (globally).

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