Wikipedia:Reference desk/Archives/Science/2021 July 7

= July 7 =

Cell phone radiation.
New article came out about cell phone radiation and brain tumor. https://www.fox32chicago.com/news/new-uc-berkeley-study-draws-strong-link-between-cell-phone-use-and-cancer But I have 2 questions, is phone radiation from smartphones different than from flip phones? (These articles don't seem to ever make a distinction.). And is it different when the phone is on a conversation, vs. not on a conversation? Thanks. 67.165.185.178 (talk) 15:53, 7 July 2021 (UTC).


 * Phone on a conversation is definitely different from phone not on a conversation. That how the system works, you have to broadcast more when you are actually using the phone. Otherwise, it only has to ping the next tower nearby.
 * Use of smartphone vs. flip phone is relevant if you are using a different cellphone network standard (3G, 4G, 5G), which might be the case or not. Different phones might also induce a different use. Say, you hold your smartphone away from your ear to see the screen, use hands-free mode if it works well, or you use a headset. --Bumptump (talk) 16:29, 8 July 2021 (UTC)

Okay I have a 2nd question: smartphone also uses the radiation for Internet, that flip phones typically do not have? So is putting your head next to a smartphone that is using the Internet, comparable to putting your head near a laptop using wireless connection? Or is that still different radiation? 67.165.185.178 (talk) 19:24, 8 July 2021 (UTC).


 * 4G, which is pretty standard for smartphones, uses LTE frequency bands. There are different bandwidth assigned depending on country.
 * WLAN, which is basically how we all connect wirelessly to our routers, most commonly uses the 2.4 gigahertz and 5.8 gigahertz bands. Each range is subdivided into a multitude of channels.
 * There are innumerable devices, besides wifi and 4G, using some share of the the radio spectrum: baby monitor, wireless speakers, toys, car alarms, garage remotes, radios proper, cordless phones, GPS, Bluetooth. The bandwidth they use is not only a technical question. They are licensed to work only within a certain range of frequencies. And they are regulated differently in different countries. But yes, in a specific country WLAN and 4G should have a different bandwidth. Bumptump (talk) 20:47, 8 July 2021 (UTC)


 * What is meant by uplink, downlink, and duplex spacing, columns, in the LTE_frequency_bands you posted? 67.165.185.178 (talk) 08:10, 10 July 2021 (UTC).


 * Uplink and downlink are explained on the notes A2 and A3 at the top of the columns - uplink is the frequency that the base station receives on, and downlink is its transmit frequency. Duplex spacing is the frequency gap between the uplink and downlink - which a little arithmetic makes plain.--Phil Holmes (talk) 09:30, 10 July 2021 (UTC)


 * Note that the current scientific consensus is that cell phone radiation has no health effect (except for heating effects). Scientific consensus can change but this is an area that has been well-studied so a single publication would need to be of outstanding quality to overturn it.
 * The actual publication from the OP's news report is hard to track down but I suspect it is this one. Being a MDPI journal is not a great look: while some MDPI journals are serious, the parent company practices predatory publishing, so unless you are in the field it is hard to know if the journal they published in is legitimate.
 * I started reading the methods of the actual article and found the criteria for the selection of primary studies a bit shaky ("Disagreements between the two authors were resolved by discussion." is not how you do reproducible research). But then I thought of reading the two comments on the article and they make clear the meta-analysis is actually crap. There is some politics (about whether studies funded by the cell phone industry were conducted appropriately to avoid influencing the results) but even if you decide to exclude industry-funded studies you need to evaluate the other studies critically. Tigraan Click here for my talk page ("private" contact)

Large ship fuel efficiency
How does the fuel efficiency of lake freighters compare with that of ocean freighters? Per tonne-kilometre/ton-mile, of course, since I assume the lake freighters are smaller because they don't need to be self-sufficient over the vast distances of the oceans. I found occasional resources that look at the fuel efficiency of lake freighters, e.g., but unless I'm overlooking something, I didn't find enough numbers to calculate what I'm looking for. On one hand, an oceangoing ship can go wherever it wants to take advantage of good weather (cf. Trade winds) or avoid bad weather, while the size of the Great Lakes means that a lake freighter can't do that, and ships in the ocean can use currents (cf. Ocean current), while a lake freighter speeded by going downstream in the St Lawrence River has to fight the same current when returning upstream. But on the other hand, lake freighters only need to carry a small amount of fuel to reach their destinations, while oceangoing ships must use extra fuel to carry around the weight of the fuel that they need to reach their destinations. Nyttend backup (talk) 16:36, 7 July 2021 (UTC)


 * I haven't got exact numbers, but looking at engine power (which is a measure of fuel usage) and cargo capacity, both of which are mentioned on the infoboxes of many ships' articles, we can get a rough estimate. I looked at the numbers of MV Edwin H. Gott and Ever Given. Assuming the ships normally run at close to full power and have an engine efficiency of around 60%, and assuming bunker oil provides around 40GJ/m3, both have a daily fuel consumption of about 0.1% of their cargo capacity. The ocean-going ship is faster though, as is usual for container ships compared to bulk carriers, so per ton-kilometre it's more efficient. Despite going faster, which increases drag.
 * Carrying enough fuel to reach the destinations doesn't appear to be a problem for either of them. Carrying the fuel to cross an ocean only takes a few percent of their cargo capacity. There are other reasons why ocean going freighters are larger than lake freighters. Larger ships have less drag compared to their displacement, making them more efficient. Lake freighters cannot be that large, because:
 * The largest ships only fit in a few ports. Ports are only made large enough for these ships if their cargo volume is huge, which is when they serve as a hub for a substantial part of a continent: Tianjin, Singapore, Rotterdam, Los Angeles, some others. As the North American Great Lakes cannot be reached by large ocean-going ships, they cannot serve as such a hub, so the ports can only handle modest ships.
 * A low cargo volume means that, using large ocean-going ships, a port would be visited by few ships. This means that the cargo has to wait in port for a long time before a ship arrives to pick it up.
 * On long distances, travel time is important. On shorter distances, loading time gets more important. Smaller ships (and the same applies to other modes of transport) allow for faster loading, as there's less to load. This is typically less important for bulk cargo.
 * On the other hand, lake freighters face smaller waves, so they can be made less strong and more streamlined, which is good for fuel efficiency. PiusImpavidus (talk) 10:21, 8 July 2021 (UTC)
 * Though not so good for ships like the Edmund Fitzgerald. ←Baseball Bugs What's up, Doc? carrots→ 00:13, 9 July 2021 (UTC)
 * Lake freighter design is limited by the ability to get through Poe Lock - 1,200 feet (370 m) long, 110 feet (34 m) wide, and the St. Mary's River at 25.5 ft deep. Smaller ones that travel both the ocean and Great Lakes are limited to Seawaymax based on the locks in the St. Lawrence River. According to our article, ships can be built longer and narrower than ocean-going ship because the Great Lakes waves have a shorter frequency reducing hogging. There is only bulk shipping on the lakes, no container ships so comparing to an ocean-going bulker would be more appropriate. MS Ore Brasil carries 5 times the load of Gott at about the same speed but uses only twice the rated engine power. So 2.5 times the efficiency, perhaps. Rmhermen (talk) 01:05, 12 July 2021 (UTC)
 * PiusImpavidus's three bullet points apply to container shipping, not to bulk shipping by self-unloaders as occurs on the Great Lakes. Rmhermen (talk) 01:23, 12 July 2021 (UTC)