Wikipedia:Reference desk/Archives/Science/2022 April 23

= April 23 =

Physics
How I can provide that after collision and before collision of the car when it was in the road and it have a passenger,,?? — Preceding unsigned comment added by 41.222.180.178 (talk) 10:23, 23 April 2022 (UTC)
 * Start at traffic collision. 2A00:23A8:4306:5D01:B995:7B23:A571:2AA9 (talk) 11:16, 23 April 2022 (UTC)


 * The question is not fully clear. Do you want to understand the physics aspects of a car collision (as in inelastic collision)? --Lambiam 16:21, 23 April 2022 (UTC)

Computed tomography scan and slices
I would kindly ask for information, I know that in spiral CTs the data of "slice thickness" and the distance between two consecutive slices "Spacing Between Slices" are important. However, I would like to understand if there is a gap in the CT that I performed between two slices. I mean if there is a "dark spot" not represented between two consecutive slices. I have found the following data of two consecutive slices of a ct, and I would like to ask if it was possible to calculate a possible dark spot, that is, if there is a gap not represented by images between two consecutive slices.

DATA: Spiral pitch factor. value: 0.65

slice thickness. value: 1.0

Gantry tilt: +8.5 — Preceding unsigned comment added by 37.161.25.209 (talk) 08:18, 24 April 2022 (UTC)

FIRST SLICE:

image position patient. value: -130.2261\-165.1111\1790.323

image orientation patient. value: 1.00000\0.00000\0.00000\0.00000\0.98902\0.14781

SECOND SLICE:

image position patient. value: -130.2261\-165.1111\1791.124

image orientation patient. value: 1.00000\0.00000\0.00000\0.00000\0.98902\0.14781

In practice the only value that changes is the third component of image position patient Δ=0.800 about.

I'm asking to myself if slices all overlap, that is, if there are not dead acquisition spaces or if there are, according to these data. It is absolutely not a medical question, I'm just a curious engineer about the data of the exam I took.

Thanks :) --37.160.236.73 (talk) 16:33, 23 April 2022 (UTC)
 * I'm not sure, but I think the beam should be minimally overlapped during the scan (to reduce patient exposure to X-rays), then the computer processes the slices into a dataset that can be rotated into whatever 3D view the technician or physician desires. Maybe one can set the settings such that slices don't overlap and leave gaps. Abductive  (reasoning) 20:01, 23 April 2022 (UTC)
 * My understanding is that a pitch factor < 1 means that the distance travelled by the scanned body during one rotation by the scanned body is less than the beam width, so there is no gap. In fact, there is some overlap, which helps in stitching the slices together to a continuous sinogram, also when the patient is not absolutely still. What is as relevant from a medical perspective as the absence of significant gaps, is the resolution. If I understand the basic mathematical principles of CT correctly, only detail that is significantly wider than the beam width will be visible in the resulting image, which is also what one would naively expect. --Lambiam 20:23, 23 April 2022 (UTC)
 * Just to confirm, pitch < 1.0 means overlap. DMacks (talk) 20:29, 23 April 2022 (UTC)
 * Thanks for answers:D! It was also my idea. Buy i read (about tilt gantry and and normal to the slice):
 * 1- http://xrayphysics.com/ctsim.html
 * 2- https://groups.google.com/g/comp.protocols.dicom/c/Qw2nWtElu2c
 * 3- https://groups.google.com/g/comp.protocols.dicom/c/lEp7NmiHIT0 that instilled doubts to me. In 5° message looks like that to calculate any spacing between two slices you have to project the reference system of patient onto the machine reference system (directory cosines). --37.163.149.54 (talk) 21:52, 23 April 2022 (UTC)

Fuel source for electricity production in the US
The war in Ukraine has raised concerns regarding Europe's dependence on Russian gas/oil. But here in the US, where we gobble power.... The New Yorker states "Electrifying your home one machine at a time is today’s Victory Garden", and referred to The Hill, which recommends "Electrifying the machines we use to heat our air and water, cook our food, dry our clothes, and take our kids to school..." So, how is the electricity produced? In the US, hydroelectric is not universally available?? Same for nuclear, wind power, solar? That leaves coal, natural gas, etc. I live in a rural area, and have used "propane" (stored in a 500 gal tank) for heat, hot water & cooking, for the past 36 yrs.

My question: Is it more effective to use fossil fuels (at a power plant) to produce electricity for the end user, versus just using natural gas or "Propane"/LPG as the end user? Thanks,  Tribe of Tiger Let's Purrfect!  21:41, 23 April 2022 (UTC)
 * The overall efficiency of "heat at the home" from various fuel-sources and routes of transmission is a popular topic. A furnace (central heating), per our article, "can be up to 98% efficient...with a typical gas furnace being about 80% efficient." That's about the most direct "burn fuel-->heat air" route. A combined cycle power plant is up to 64% for electrical generation, and then there would be further losses when that electricity is converted to heat at the home. However, even the poorest heat pump has a coefficient of performance higher than two, so when that device is used for heating, it more than makes up for the lower efficiency of the electrical generation. This is all just back-of-the-envelope...I'm sure it's been analyzed in more detail in many published references. DMacks (talk) 23:05, 23 April 2022 (UTC)
 * Thanks, this is helpful. Tribe of Tiger Let's Purrfect!  20:54, 24 April 2022 (UTC)
 * The question does not take into account the likelihood of commercial electricity generation itself becoming less and less dependent on fossil fuels in the future.
 * In my own country, the UK, non-fossil fuel sources (other than Nuclear power) were a negligible component of National Grid electicity supply well into my adult lifetime; as I type right right now (in the middle of the night), fossil fuels are supplying only 16.62% of the total demand, with the rest coming from Nuclear and Wind power, renewable Biomass (using purpose-grown trees and sawmill waste), plus 0.62% of Hydroelectricity. During the day Solar power makes significant contributions (averaging around 20% at noon over the past week), and stored Hydroelectic power is deployed around dawn and dusk to smooth out transitions. (See this handy site.) The trajectory is to continue reducing routine fossil-fuel use to near-zero over the coming decades.
 * Assuming the USA chooses to follow the same trajectory, supplied electricity there should also become increasingly non-fossil derived, so domestic electrical appliances will become increasingly less dependent on fossil fuel without the homeowner even having to do anything further to bring this about. Moreover, as the technology improves and economies of scale ramp up, increasingly efficient home installations of solar power panels and heat exchangers (as technology advances) can also be deployed where possible to reduce dependence on external supply and even yield income by selling power to the grid.
 * Note that "efficiency" of supply won't matter a damn if the place one lives becomes uninhabitable due to the effects of Global warming largely caused by fossil-fuel use. I personally expect this to happen in the South Western states of the USA around 2050 unless drastic measures are implemented, but I'm not an expert. {The poster formerly known as 87.81.230.195} 90.197.101.71 (talk) 02:13, 24 April 2022 (UTC)
 * You might want to check the EIA's prediction of fuel source for electricity 2022-2050. Bit of a drop in coal, more gas. https://www.eia.gov/outlooks/aeo/pdf/AEO2022_ChartLibrary_Electricity.pdf p5 Greglocock (talk) 07:38, 24 April 2022 (UTC)


 * I was unaware of stored Hydroelectic, until I toured a facility in northern England. What a marvel of engineering! Another "savings" unfamiliar to a US person, were the small units that supplied "on demand" hot water for showers. Our UK hosts did have a traditional electric-powered boiler/hot water heater, but it was set on a timer, to provide hot water for laundry, cooking, and dishwashing, within a set number of hours after work, and then shut off. They used gas for cooking, and for the modest, but warming, gas fireplace in the living area. The gas was supplied on a pay-as-you-go system. Located in a cupboard, was a small device, that they fed with coins. On a regular basis, someone would come to collect the money. Pat explained that the device wouldn't except "modern" coins, so when she met the employee, she would pay the equivalent in modern coin, and keep the old coins that the device accepted.


 * We became accustomed to the shower water heaters, which were always present in the inexpensive B&Bs, which we preferred. At one inexpensive hotel, the shower heater was coin operated...so sensible! It didn't take long to figure out that the reason my husband always offered/insisted that I take the first shower in a new place, was so I would figure out how the device worked, and then tell him what to do! Great fun, late 1980s to late 1990s. Tribe of Tiger Let's Purrfect!  20:29, 30 April 2022 (UTC)
 * Our article say that the US uses about 40% natural gas, 20% coal, 20% nuclear and 20% renewables for its production of electricity, so that's about 60% fossil fuels and the coal is worse than the propane you burn at home. The efficiency of fossil fuel power stations is around 50%. The most modern units reach around 60%, some claim a bit more as they say they found some use for their waste heat, but the oldest units still in use are around 40%. When you want high temperature heat (like in cooking), this electricity can be turned into heat only by resistors (induction cooking also uses a resistor, the cooking pot itself), so the efficiency is 50%. A gas stove has limited efficiency too, assuming the burners aren't too large around 60% or so, so for cooking, electrifying right now may not be much of an improvement, but gets better as the proportion of fossil fuels in electricity generation falls.
 * For low temperature heat, you can use heat pumps. A properly functioning heat pump has a coefficient of performance more than high enough to compensate for the losses in a fossil fuel power station. Unfortunately, heat pumps don't always function properly. In temperatures close to freezing and moist air (which, depending on your climate, may be when you need most of your heating), many types (in particular the more affordable ones) can get clogged with ice, turning them into resistive heaters, which is worse than heating your home with gas directly.
 * So, yes, electrifying your home helps, but it's not magic. Try to cut back on energy use, get solar panels if you haven't already and tune you power consumption to match generation of the solar panels during the day. And I've got no kids, but when I was one myself, I went to school by bike. Fully muscle powered, it doesn't get cleaner than that. PiusImpavidus (talk) 09:29, 24 April 2022 (UTC)
 * In California where I live, as of 2020, electricity is generated 48% by natural gas, 15% by solar, 11% by hydroelectric, 9% by nuclear, 7% by wind, 6% by geothermal and 3% by biomass. Coal, oil and waste heat are negligible factors here. See this government report for details. Cullen328 (talk) 02:44, 27 April 2022 (UTC)


 * I experienced heat pumps in the early 1980s, northern TN and NC. Very humid climate, regularly below 32F and as low as 9F. Heat pumps were a misery in winter, pumping out cold, clammy air. My husband grew up in NY state, where they had radiators. We built a modest home (NC), 1986, with gas heat, water & stove, electric AC. Even now, in our mid-late sixties, thermostat is set for 55F, winter...78-80F, summer. Our attic fan is very helpful in spring & fall. Growing up in NC & SC, there was no AC, we used floor fans. I'm willing to give up gas, except for the stove burners. Solar would be good, except that we live in a thick deciduous forest, only so many hours, even in winter, that we have direct sun on the roof. At my age, not certain if it's worth the long term investment.  Tribe of Tiger Let's Purrfect!  21:06, 30 April 2022 (UTC)