21

Just Chat! / Re: Education review and impressing rights and freedoms, democracy, myth busting.

« on: 02/09/2018 16:36:24 »

Good deeds do not require supernatural justification. The only rational reason to spend time appealing to the supernatural is therefore to justify or excuse evil deeds.

22

Geek Speak / Re: Can you recommend how to protect a clinic lab from malware?

« on: 02/09/2018 16:13:04 »

I built a diagnostic imaging clinic with two physically separate networks. All patient clinical data and images circulated on one "clean" system with no direct connection to the outside world. Anything that had to leave the premises  did so through a push-only port to the "dirty" server where it could be picked up and attached to invoices, emails etc., along with any incoming medical records, scan requests, facebook, pornography and advertisements that got though the firewall.

Equipment performance monitoring and updates went through a separate processor and a dedicated data line to the factory with no internet capability.

Grumbles about the cost of "why two servers and all that hard wiring" etc when I set it up (servers cost £5000, MRI unit cost £1,000,000), and muttering about "no Amazon in the control room" (go shopping in your own time, please). No breaches or crashes in 15 years.

23

The Environment / Re: Are thunderstorms more common in the afternoon?

« on: 25/08/2018 21:18:32 »

Yes. Particularly in summer, more rain falls in mid-afternoon (thanks to convective cloud precipitation) than at other times, but the difference is less noticeable in winter when most of the rain is advective rather than convective. However it is also the case that official daytime in Cambridge lasts almost 17 hours in June and less than 8 in December, so if the rain fell continuously, it would mostly fall at night in winter.

PS. The Camelot myth having now been assigned to Tintagel, "it do rain there most of the bloody time, me dear."

24

New Theories / Re: NFEU MODEL

« on: 25/08/2018 14:57:53 »

Inspired brilliance.

This kind of meaningless drivel belongs in the catalog of an art gallery, the program notes of some egregious modern composer, or a postgraduate seminar in quantum philosophy. Don't waste it on mere seekers of wisdom.

25

General Science / Re: What are the common methods to quantify accuracy and precision?

« on: 25/08/2018 11:57:38 »

Let's play a little bit by estimating the value of π, and sort out the answers below by their accuracy and precision.
A   3.14159265358979  true as far as it goes
B   3 good enough to estimate the value of a reasonably fit tree from its widest diameter
C   3.00 an economist's forecast: misleading implication of precision
E   3.14 good enough for carpentry
F   3.15 wrongly rounded
G   3.14159265 good enough for most navigational and engineering purposes
H   4.14159265358979 dangerously wrong
I   3.14159265358979 +/-1 wrong statement of error. should be +0.5 x 10^-14/-0 because we know the true sum of any usefully convergent pi sequence exceeds the truncated value
J   3.14159265358979 +/-10 see I above
K   between 3 & 4 a politician's statement: literally true but ambiguous and potentially misleading: it is a constant
L   between 5 & 5 Trumpism. The greatest value of pi - ever! The evil fake news media want to deprive you of your right to thirty seven percent of your American heritage by insisting on a number that even the ancient Greeks knew was irrational. And now Greece is bankrupt. Pi is five! Pi is five! .....

26

The Environment / Re: Are thunderstorms more common in the afternoon?

« on: 24/08/2018 16:00:05 »

Convective clouds produce most shortlived summer thunderstorms over a wide area all at once. Sun shines on moist ground, damp air rises rapidly into cold upper atmosphere and accelerates upwards because it doesn't cool as quickly as the rate of ambient temperature decrease with height ("lapse rate"). Once above the condensation level this accelerates faster and forms towering cumulus or cumulonimbus clouds, and convection within these clouds makes water droplets and ice crystals rise and fall, creating a potential difference between the top and bottom of the cloud (see the Kelvin electrostatic generator on this forum https://www.thenakedscientists.com/get-naked/experiments/electricity-water-kelvin-water-drop-generator ). Eventually this will discharge to another cloud or to ground.

Summer "fine weather" cumulus clouds take time to grow, so at UK latitudes are unlikely to reach electrical instability until some time after the maximum solar heating, say 2 - 3 pm (local time is distorted by ridiculous "daylight saving" clock aberrations) but it may happen quicker at lower latitudes. They usually disperse after sunset.

Advected frontal storms last for a longer period and form in a moving  line rather than a static area as a cold polar air mass rolls over warm (and therefore moist) tropical air. In the UK the line usually moves west to east at about 20 - 30 knots and can hit any point at any time of day or night. Most likely to be found along a cold front on a weather map, but a real nasty can occur when the cold front (which generally moves faster than a warm front) overtakes a warm front to produce an occlusion. This can look from below like harmless mist and drizzle with a benign covering of stratus so off we go into the wide grey yonder, only to break through the stratus at 5000 ft and find all hell going on upstairs - "embedded CuNim" chucking snow, hail and lightning all around you, up to 60,000 ft, in the middle of the night. Study and avoid.

27

General Science / Re: What are the common methods to quantify accuracy and precision?

« on: 22/08/2018 07:01:11 »

Effectiveness: capability of producing a desired result. So you need to define the desired result. This should not be "hitting the exact centre of the target", which is probably unachievable, unprovable and generally unnecessary,  but "disabling the enemy", which means getting within say 0.5 m of the centre of the target. Pinning down this specification is often the key to contract negotiation: what would be considered "good enough"?

Efficiency: reward divided by effort. This may be multidimensional. Back to the military analogy: a machine gun may be adequately effective especially against a moving target and can be operated by a relatively nonspecialist crew but it needs a lot of supplies and announces its location. A sniper rifle needs one specialist operator but is supremely effective against a stationary target, with limited supplies.

Once you have agreed numbers for effectiveness and efficiency, the "engineering" aspects of a project, you can start looking at the "scientific" options for obtaining the accuracy and precision required to meet the specification.

Your phrase "only done once" may be significant. Years back I had all sorts of problems with unreliable medical x-ray machines. They had been built with wonderfully precise electromechanical servo systems which, the manufacturer assured me, were the best - they were used in guided missiles. Problem is that a diagnostic medical x-ray generator has crude accuracy requirements of around ± 5% on three parameters (voltage,current, time) but has to work  several hundred times a day for 10 years, whereas a guided missile requires supreme accuracy but only needs to work once!

Focussing on your problem, you can separate out random errors (tolerances) from systematic errors (traceability) and add them separately in quadrature (√[a² + b² + c²...]) to estimate precision and accuracy of a single shot respectively. If the total lies within the "kill circle" or whatever your customer agrees for a specification of effectiveness, you have a product.

28

Physics, Astronomy & Cosmology / Re: Has permittivity had the same value over the observed lifetime of the universe?

« on: 13/08/2018 16:06:29 »

The permittivity of "free space", ε₀, is the "measured" value for a vacuum (or as close as we can get to a vacuum).

It is unlikely that the true value of ε₀ would vary with time as the concept of "vacuum" is absolute. However the relative permittivity ε_x where x is the primordial stuff that filled the universe before whatever happened, happened, would probably have had a higher value - it could not have been lower.

29

Physics, Astronomy & Cosmology / Re: Can we feel gravitational attraction from objects at different velocities?

« on: 12/08/2018 18:40:31 »

In principle, yes. In practice, it's a very small force unless the moving object is very large.

Given several billion years and a lot of resonance effects, the motions of the moon and sun are responsible for moving tides. At the laboratory level, it is worthwhile considering Cavendish's experiment to determine G  by the effect of a large stationary mass on a moving object, as was Maskeleyne's use of a pendulum to measure the mass of a mountain. At the astronomical level, it is the perturbations of distant planetary orbits by "something moving" that led to the discovery of Neptune and Pluto.

30

Physics, Astronomy & Cosmology / Re: Can the speed of light represent zero velocity?

« on: 12/08/2018 16:06:51 »

we exist in a region of the cosmos which is travelling at a velocity of 186,000mps,

Relative to what?

31

General Science / Re: Will rust on my de-stemmer affect my grape juice?

« on: 12/08/2018 14:22:39 »

Every great winery has a secret ingredient. Usually a dead rat.

32

Question of the Week / Re: QotW - 18.08.05 - Who counted all the stars in the universe?

« on: 09/08/2018 15:22:18 »

Nobody. But we have counted enough galaxies, and (by assuming the universe is fairly isotropic) made sufficiently reasonable estimates of the average number of stars in a galaxy and the probable number of distant galaxies too faint to distinguish, to come up with an estimate of the number of stars in the observable universe.

Only human vanity assumes that the observable universe is all that there is. There is no reason to suppose that it ends at the Schwarzchild radius, and every reason to believe it doesn't. So the whole universe is likely to be a lot bigger, and possibly a lot weirder, than the bit we can see.

Estimating the number of grains of sand is a bit easier - if you have a definition of a grain.

33

General Science / Re: How are electricity towers designed?

« on: 09/08/2018 11:47:08 »

Start with the statutory clearance of the conductors from each other and whatever they pass over.

Specify the conductors according to the intended maximum working current

Calculate the insulator length required for the voltage and assumed weather conditions

Calculate the catenary drops between pylons for the specified design tension of the conductors

Design the simplest tree structure (single vertical insulators) required to support a straight run, allowing for windage and the weight of the wires between pylons

Calculate the straight-run pylon spacing required by the clearance, insulator lengths and catenary drops

Determine the maximum tolerable angular deflection between adjacent straight runs

Design the tree structure required to anchor each turn that exceeds that value (pairs of horizontal insulators)

Consider whether additional tensioning or tension relief trees (horizontal insulators) are required between the simple trees

Design any junction or terminal trees that may be required

Now go to an applied maths textbook and look up "just stiff structures" to support the outline trees you have drawn

At this point the geologists, accountants, countryside preservation planners and electrical load planners will tell you that the proposed route and capacity have changed.

34

General Science / Re: Should I ask a doctor about stopping smoking?

« on: 06/08/2018 19:50:36 »

The only way to stop smoking is to stop smoking. People will thank you. Don't ask for help of any sort because quite frankly nobody cares how much you spend killing youself, as long as you don't exhale over them. But doctors and pharmacists will take your money as happily as the tobacco companies.

35

Question of the Week / Re: QotW - 18.02.04 - Do lobsters experience pain?

« on: 05/08/2018 14:00:03 »

A brilliant analysis, flawed only by the obvious truth.

Lobsters do not attempt to mate with any other species, but are attracted by other lobsters. The males will fight with other males for mating priority and the females may reject their suitors. Therefore lobsters have at least a "rudimentary level of selfawareness" that distinguishes "I" from "he", and "us" from "everything else". Pretty much the same applies to all other animal species.

Unlike terrorists and football hooligans who only recognise "we" and should therefore be boiled. 

36

Question of the Week / Re: QotW - 18.07.29 - What is the minimum area required to sustain one human being?

« on: 27/07/2018 08:26:58 »

The area of the UK is about one acre (0.4 hectare) per person. When fully cultivated, the country was just about sustainable at 20th century standards of living when we had a coal industry. For indefinite sustainability without fossil fuels we would need to reduce the population to not more than 20,000,000.

At a population of 5,000,000 (around 10 acres per person - roughly the population density of the USA) the quality of life in the UK would be better than any civilisation has ever experienced, and indefinitely sustainable. However the attractiveness of such a society would lead to threats of invasion followed by mass immigration and a diluition of that quality, so as we reduce the population (as we surely must) we need to deploy more personnel defending our very long coastline - we may need to settle at 10,000,000.

37

Physics, Astronomy & Cosmology / Re: How real is (my understanding of) the Copenhagen Interpretation?

« on: 27/07/2018 00:14:25 »

Another important point, that has been mentioned in this thread, but not explicitly focused on is this: Nothing can ever be known exactly--there is always some uncertainty.

It is absolutely crucial to distinguish between uncertainty - the confidence limits of a measurement - and indeterminacy - the fact that ΔpΔx ≥ h.

We can measure the density or x-ray diffraction pattern of solid hydrogen and thus deduce the effective diameter d_H of a hydrogen atom with an uncertainty of, perhaps, ± 0.1% But the fact that  d_H >> d_proton is due to the indeterminacy of the electron.

38

General Science / Re: Is zero an even number, odd number, or neither?

« on: 25/07/2018 22:25:56 »

An integer is a counting number. It is a response to "how many?" I have 0 friends. 0 is an integer.

39

General Science / Re: Is zero an even number, odd number, or neither?

« on: 20/07/2018 13:42:15 »

An even number is an integer which is "evenly divisible" by two. This means that if the integer is divided by 2, it yields no remainder. Zero is an even number because zero divided by two equals zero, which despite not being a natural number, is an integer.

40

Just Chat! / Re: Would it be illegal to ?

« on: 14/07/2018 16:07:42 »

So do as the man says. Buy one lottery ticket and win the £10k you need to start the next phase. When you have won £1,000,000 show me the evidence (a suitcase full of fifties will suffice) and I'll help you develop the project. The promise of certain world domination and my eternal friendship for £1 is surely attractive, and you can probably  find £1 between the sofa cushions..