Author Archives: gmcdavid

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About gmcdavid

Retired IT professional with a wide range of interests. Married. Three sons, two with autistic-spectrum disorders and the third being transgender with Ehlers-Danlos syndrome. From Chicago but now living in the Twin Cities metro, Minnesota. Episcopalian. Carleton College (BA 1972, physics) and Stanford University (MS 1974, Applied Physics; MS 1976 Statistics).

Greek and Roman sling messages

From Writing funny stuff on ammo is over 2000 years old:

Know those great photos of World War II crews painting bombs with messages like “Easter Eggs for Hitler” or “To Mussolini, with Love”? It turns out, your ancestors have been doing that for over 2,000 years, because the British Museum has sling shot from 300 B.C. where missileers were telling the enemy to “Catch!” their shot.

The British Museum has a good example.

“Catch” is one of the tamer examples. From Humorous Inscriptions on Lead Sling-Bolts (Sling Bullets; Slingshot) Reflect a Roman War of Words:

Some NSFW examples follow

Rang Gaeilge, 22ú lá Mí na Nollag 2020

Duinnín agus an Bhean nár tugadh Nimh di

There is a slightly different version of the story at Feasta.

Neimh, ­e, f., poison venom, virulence, pus. . . neimh na ndúl i ngrúg na gaoithe, all the venom of Nature in the fury of the wind (Kea.). . . Tá neimh na meanadh ar an snáthaid, the poison of the awl is on the needle (of inherited qualities); domlas dragúin agus neimh thríd suaidhte go mbadh é deoch do shuain é ar uair do bháis.. . .

dúl = dúilelement (of creation)
grúgAnger, displeasuref
domlasgall, bile
dragúndragoon; dragonm
suaidhte
badh
suanSleep, slumberm

  • Bhí an bhean bheag liath roimhe[?] ina pharlús nuair a d’fhill an tAthair Pádraig Ó Duinnín ón leabharlann Náisiúnta go dtí an bungaló i bPort Mhearnóg mar a mbíodh cónaí air. Ní raibh tine ar lasadh ann agus bhí taise an fhómhair agus taise an tsáile sa pharlús. Bhí an beanín, cuachta ina cóta liath, suite ar imeall cathaoireach. Ainneoin an fhuachta, bhí péacáin allais ar a héadan. D’éirigh sí go scáfar nuair tháinig sé isteach.

    The little gray woman was in his parlor before Father Patrick Dineen returneed from the National Library to the bungalow in Portmarnock where he lived. There was no fire lit and the dampness of the autumn and the moisture of the sea were in the parlor. The little woman, wrapped in a gray coat, was seated on the edge of a chair. In spite of the cold, there were drops of sweat on her face/forehead. She rose up timidly when he came in.

    taiseDampness, moistness, humidity; softness, smoothness, tenderness; mildness, gentleness; kindness, compassion; Fetch, wraithf
    sáileSea-water, sea; Ease, comfortf
    cuachtabundled, wrapped
    imeallBorder, edge, rim, marginm
    Ainneoinnotwithstanding, in spite of
    péacánSprout, shoot, plumulem
    éadanfacem
    scáfarFearful; Frightful, dreadful; Timid, apprehensive

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Significant Figures

I found this post on Facebook: Why is it important to know so many digits of pi?.

My comment:

As someone who started computing with log tables and slide rules, the first question I ask is how many significant digits do the other variables in your calculation have? The smallest such number tells you how many digits of pi you need. With electronic devices there is no harm in using more in your calculation, as many as your device has, but do not let that give you a false idea of the precision of your result.

I learned about significant figures in my high school chemistry in 1967-68. (Thank you, Mr. Wheeler!). Use of appropriate significant figures, also from a chemistry class, clearly explains the concept and its use in practice.

I only first saw Star Trek (TOS) after high school, in reruns. Thanks to that chemistry class I gag every time I hear Mr. Spock reporting some calculation to an absurd number of decimal places. His input data could not possibly be that precise!

Science Fiction got there first (again)

Back in High School (1964-68) I read a lot of science fiction by Mack Reynolds. His Joe Mauser series is set in a world where the cold war continues into the 21st century, but, to avoid catastrophe, the West and the “Sov-world” have agreed to restrict all military forces to pre-1900 technology. There is still lots of fighting going on at that level.

Recently I was reading about the decades old border dispute between between China and India countries, which actually led to war in 1962. The conflict still simmers on, but a 1996 agreement states that

Neither side shall open fire, cause bio-degradation, use hazardous chemicals, conduct blast operations or hunt with guns or explosives within two kilometers from the line of actual control.

Neither side wants to get the blame for starting a shooting war, so both sides are following the letter of the agreement. However, nobody is backing down. There have been reports that “Chinese troops have used improvised edged weapons, such as nail-studded clubs, in … skirmishes with Indian forces.” and both sides have martial artists in their border forces.

It seems that the Chinese are escalating. We now have Chinese soldiers armed with new devices for hand-to-hand combat with Indians in Tibet. Actually the “new device”, the guan dao, is quite old. It similar to a a western medieval halberd. It will be interesting to see how Indian army responds. They have a rich tradition of edged weapons to draw upon.

Calculating a limit

Today I saw this problem on Medium: Compute the limit

Followed by “Pause the article and attempt a solution now.” (Don’t cheat and look ahead)

So I did. I do not really like factorials, so I immediately thought of Stirling’s approximation:

ln n! ≃ n ln nn as n → ∞

and all of the n‘s cancelled, leaving the result 1/e. I then looked at the author’s solution. My answer was correct, but he used a completely different approach, as you can see. I posted my solution, and got a nice complement from him.

This is Thanksgiving day in the USA. I am thankful that my calculus skills are still pretty good decades after my last formal course in that or any related field .

Rang Gaeilge, 24ú lá Mí na Samhna 2020

Duinnín agus an Cat (tuilleadh)

  • ‘Tá an gloine briste i ndoras uimhir a 33,’ arsa Eleanór, ‘díreach mar a bheadh i ndoras Mharia murach gur imir tú cleas ar an nglas.’
    ‘Féach an sneachta os comhair an dorais [g],’ ar sise. ‘B’é go raibh cruinniú poiblí ar an táirseach?’
    ‘Dráma, seachas cruinniú, déarfainn,’ arsa an Duinníneach. ‘An rian is tábhachtaí ná an ceann sin ar clé ar fad.’
    ‘Is geall le rian coise eilifint é.’

    ‘The glass is broken in door number 33,’ Eleanor said , ‘just like it would be in Maria’s door if you hadn’t played a trick on the lock.’
    ‘Look at the snow in front of the door,’ she said. Was there a public meeting on the threshhold?’
    ‘Drama, rather than a meeting, I would say,’ said Dineen. ‘The most important track is that one on the far left. It is like an elephant’s footprint.’

    cruinniúGathering, Meetingm
    poiblípublie
    táirseachthreshhold
    rianCourse, path; Mark, trace, track; Power of movement, vigorm
    geallPledge, security; Wager, bet; promisem
    Is geall leIt is like

  • ‘Cuimhnigh go raibh bróga tí á gcaitheamh ag Maria. Faoin am seo, bheidís báite fliuch agus éadach na n-uachtar ag sliobarnaíl thar na boinn. Tá na coiscéimeanna eile anuas ar na cinn aici siúd.’
    ‘An méid atá iontu!’ arsa Eleanor go himníoch. ‘Fiú agus méadú le linn leá a chur san áireamh! . . . Feicim fathaigh, abominable snowmen, dosaen garraíodóir ar thóir Mharia.’
    ‘Siúil anseo i lár an chosáin mar a bhfuil an sneachta leáite.’
    ‘Fuil!’ arsa Eleanór agus uafás uirthi.
    ‘Braonta ar fud na háite,’ a d’aontaigh an Duinníneach.
    Chuir sé lámh trín bpoll agus d’oscail sé an doras.

    Remember Maria was wearing house shoes. By this time, they would be drenched wet and the cloth on top drooping over the soles. The other footsteps are on top of hers.
    ‘The size of them!’ said Eleanor anxiously. ‘Even considering the increase during melting! . . . I see giants, abominable snowmen, a dozen gardeners in search of Maria.’
    ‘Walk here in the middle of the path where the snow has melted.’
    ‘Blood!’ said Eleanor in horror.
    ‘Drops all over the place,’ agreed Dineen.
    He put his hand through the hole and opened the door.

    báitedrowned
    éadachclothm
    uachtartop, upper part; creamm
    ag sliobarna = ag liobarnahanging loose, drooping
    bonnsolem
    méadúincreasem
    leámelting, dissolutionm
    áireamhcounting, reckonning
    fathachgiantm
    ar thóirin search of
    cosán Path; Footway, track; Way, passage; directionm
    fuilbloodf
    uafásHorror, terrorm
    aontaighunite; agree

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Water on the Moon

It’s confirmed. There is water on the Moon. OK, what’s the big deal? Water is very common in the cosmos and has been seen on the moon before. The difference is that previously it had been been only in craters near the lunar south pole, perpetually in darkness. Now, as the updated NASA announcement said, NASA’s SOFIA Discovers Water on Sunlit Surface of Moon, which will be much more accessible to future explorers.

How significant this is remains to be seen, but it has provided Katie Mack with some inspiration.