Wikipedia:Reference desk/Archives/Science/2023 January 20

= January 20 =

Dependence potential of physical exercise and social media
We have this nice chart comparing the dependence potential of various drugs. How would physical exercise (Exercise addiction) and social media (Social media addiction) compare? Do we have sources on that? a455bcd9 (Antoine) (talk) 08:37, 20 January 2023 (UTC)


 * I'd also like to see their effective dose/lethal dose ratios. --Lambiam 10:43, 20 January 2023 (UTC)
 * The "dependence potential" scale is not calibrated, so it is not clear what should be compared to what. The source on which the chart is based lists three ways to "measure" dependence potential, one of which is entirely subjective, and then fails to reveal which one was used in the subsequent table. In another publication, "Toward a Comparative Overview of Dependence Potential and Acute Toxicity of Psychoactive Substances Used Nonmedically", the same author promises in the abstract that "[a] procedure is outlined for comparing dependence potential and acute toxicity across a broad range of abused psychoactive substances." The paper contains a very similar table. However, perusing the paper does not really explain the scale, other than that "about 350 articles" read by the author that "were found to give ... an empirically derived comparison of dependence potential ... constitute the database of findings reported here". This procedure, as outlined, is not even amenable to replication for the substances rated in this article, let alone for activities. --Lambiam 11:14, 20 January 2023 (UTC)

Questions about the output of cascaded but damped Goertzel filters
I have been experimenting with cascading Goertzel filters with decay (better known as resonators) in series on in an attempt to create the more optimized version of the sliding windowed infinite Fourier transform, why the magnitude output $$\sqrt{f_1^2+f_2^2-\mathrm{coeff}*f_1*f_2}$$ of the cascaded Goertzel filters have small amplitude modulations and how to normalize the output correctly? 2001:448A:304B:18C2:85DA:D596:AFD3:58FB (talk) 14:47, 20 January 2023 (UTC)
 * My response at the Miscellaneous desk provides some references. Philvoids (talk) 22:58, 20 January 2023 (UTC)

AC vs HVDC to the naked eye
Dear Wikipedians:

Is it possible to tell with one's naked eye at a glance whether a particular transmission tower is carrying AC or HVDC?

Thanks, 173.209.130.10 (talk) 20:45, 20 January 2023 (UTC)
 * Looks like there are two wires hanging from each insulator on HVDC pylons, and only one per insulator on AC pylons. Abductive  (reasoning) 21:49, 20 January 2023 (UTC)
 * I assume this is about power transmission through overhead power lines. The role of the towers is a purely passive one: to keep the lines high up. However, the lines may give away the system. For high-voltage AC transmission, typically three-phase electric power is used, and then the lines come in groups of three, like here  with two groups of three. For high-voltage DC, either one or two lines are used. Two is more common. Note that a line may have multiple strands, as seen in  this photo, with a two-strand line on either side. However, two lines are also occasionally used for relatively low-voltage AC systems, which then typically will be single-stranded. To complicate the issue, the towers may support sets of conductors for both types. So there is no foolproof criterion, but if there is only a single line, it is certainly DC, and if you see only groups of three, it is AC. Note that some visible lines may not be conducting lines and should not be counted. The conducting lines are recognizable by being separated by a stack of insulators from the suspension points.  --Lambiam 22:05, 20 January 2023 (UTC)
 * Look where the power line leads. A transformer substation that emits a 50 or 60 Hz audible hum is evidence of AC. Philvoids (talk) 23:06, 20 January 2023 (UTC)
 * Although detecting an audible hum with one's naked eye at a glance would probably require a good dose of LSD or similar. nagualdesign 02:40, 21 January 2023 (UTC)
 * Far out, man. David10244 (talk) 08:12, 21 January 2023 (UTC)
 * There's always the possibility of synesthesia. --142.112.220.65 (talk) 10:08, 21 January 2023 (UTC)
 * Please respect the rule No narcotic advice and don't promote "a good dose of LSD", a psychoactive Hallucinogen that has no approved use in medicine. Philvoids (talk) 10:43, 21 January 2023 (UTC)
 * In the interests of strict accuracy, LSD is not a Narcotic: was clearly not making any kind of medical recommendation, and using "good" in the sense of "sufficient" rather than as a term of approval. {The poster formerly known as 87.81.230.195} 90.197.179.175 (talk) 20:19, 21 January 2023 (UTC)
 * Thank you, . I thought it would be obvious that my previous comment was a tongue-in-cheek reminder of the OP's question, but there's always one isn't there. Perhaps I should add that LSD will probably not enable you to see the hum of a substation, and if it did induce synesthesia you'd probably be too distracted to remember that you were trying to determine whether a power line was AC or HVDC. nagualdesign 20:23, 22 January 2023 (UTC)


 * Taking a hierarchical look:
 * One or more wires may be stranded to create a cable. In real life, a single wire is only used for very small applications or as contact wire in railway electrification. Cables are easier to handle and high-voltage transmission always uses a steel core for strength and an aluminium outside for conductivity.
 * One to four cables may be packed together in a bundle. These cables are not insulated from each other, but there usually are separators to keep them a fixed distance apart. The advantage compared to a single, thicker cable is that a bundle is easier to handle and has a lower electric field on its surface, limiting losses. The entire bundle is insulated from the tower using long insulators. With some experience, you can estimate the voltage from the length of the insulators.
 * One to four bundles form a circuit. A single bundle can't form a complete circuit, so these are used on HVDC lines with earth return. Two bundles normally indicates DC, three bundles AC, as it's transmitted as three-phase power. Four bundles can be three-phase power with a neutral, but this is only used for short distance distribution, not for transmission.
 * One to four circuits (sometimes more; I know one short line with six circuits) can be carried on a single transmission line. The line may also carry lightning protection wires, which are thinner, not insulated from the tower and on top. Birds perching on transmission lines usually do so on the lightning protection wires.
 * So, if the number of bundles is a multiple of three, it's normally AC, but if it's a multiple of two, it could be DC. There are some caveats though:
 * In countries with low frequency AC railway electrification, there may be a separate power network for this low-frequency AC. As these trains use single phase AC, the power lines only have a multiple of two bundles (normally four, so two circuits).
 * Short distribution lines may also use single-phase AC, but these are not used for transmission.
 * Six is a multiple of both two and three, but transmission lines with two AC circuits are far more common than transmission lines with three DC circuits.
 * For large spans, the bundles of a single circuit have to be some distance apart, so you may end up with three lines of one bundle each.
 * Different systems may share a single transmission line. For example, you could have seven bundles: one circuit for three-phase power and two circuits for railway power.
 * Sometimes, you can also tell AC and DC apart by ear: AC lines can produce a faint transformer hum. Transmission lines can also make other noises, which can be heard on HVDC lines too, but if there's a clear 100 or 120 Hertz sound (depending on your country), it's AC. PiusImpavidus (talk) 12:28, 21 January 2023 (UTC)

Many thanks for so much contributions! 173.209.130.10 (talk) 18:56, 21 January 2023 (UTC)