blog

Over the last few weeks, I have start­ed pick­ing up trash on the way to work.

At the moment, one of the great bless­ings of my life is that I get to cycle to work, on a beau­ti­ful path along the riv­er. There is a lit­tle stretch where there is a lot of lit­ter among the trees and bush­es. It nev­er gets picked up (I have great appre­ci­a­tion for the hard work the munic­i­pal work­ers in my city are doing, nev­er­the­less I dis­agree with how they take care of plants and lit­ter). It occurred to me this win­ter that instead of com­plain­ing to myself that the lit­ter does not get picked up, I could do some­thing about it. It took months to final­ly start, but I am so glad I did!

The first sur­prise is that there is a lot of trash. It is almost frac­tal — the more you look, the more you find, since the lit­ter breaks down with time and gets cov­ered by the plants and fall­en leaves. It also keeps com­ing back, as peo­ple keep lit­ter­ing reg­u­lar­ly. And all this on a tiny, 200-metre stretch of land in one of the most eco­log­i­cal­ly-con­scious coun­tries in the world.

The sec­ond sur­prise is how easy it is to just pick up trash. There was a large psy­cho­log­i­cal bar­ri­er to over­come before I could start, but the very moment after I pulled out my first lit­tle plas­tic bag, things became easy. Pick­ing up trash requires no prepa­ra­tion and so very lit­tle effort. Three times a week, I spend maybe ten min­utes fill­ing up a small bag on my way to work, throw away the bag in a bin togeth­er with my sin­gle-use glove, and then I get to see the result on the way back in the evening.

A great part of the spark came from see­ing, three years ago, a pho­to of Gary Chris­ten­son, May­or of Malden (MA, US) on the inter­net. Any­way this just to say, if you are hes­i­tat­ing too, go for it!

Je suis revenu sur mon expéri­ence avec mon livre de ther­mo­dy­namique dans un arti­cle pub­lié aujourd’hui sur le Fram­ablog : Mais où sont les livres uni­ver­si­taires open-source ?

Cette année, le pro­jet Wiki­me­dia Com­mons, la base de don­née mul­ti­mé­dia qui se cache der­rière les pro­jets Wikipé­dia, fêtera son dix-huitième anniver­saire. Je con­nais bien cette com­mu­nauté puisque je m’y promène presque tous les jours, pour le tra­vail et mon loisir, depuis dix ans. Wiki­me­dia Com­mons est une cav­erne d’Ali Baba, incon­tourn­able pour l’édition d’un de doc­u­ments édu­cat­ifs libres. C’est là que vous allez pou­voir trou­ver, dépos­er, amélior­er les pho­tos, sché­mas, dia­grammes dont vous avez besoin : par exem­ple, le cir­cuit d’eau d’une cen­trale ther­mique, une image de 400 megapix­els de la baie de San Fran­cis­co, une illus­tra­tion sor­tie d’une pub­li­ca­tion de recherche pub­liée en 1820 ou un sché­ma vec­to­riel illus­trant la notion math­é­ma­tique de dérivée en espag­nol. Mal­heureuse­ment, on dirait que quelque chose s’est coincé et que le pro­jet est resté figé en l’an 2000. Me croirez-vous si je vous dis que l’entièreté du pro­jet — son sys­tème de mesure de qual­ité, d’organisation interne, et surtout, toute sa base de don­nées — est basée sur du wiki­texte ? Wiki­me­dia Com­mons est un pro­jet unilingue, qui souf­fre d’un manque cat­a­strophique de diver­sité. Il est fait surtout d’éditeurs ama­teurs (j’en fais par­tie) qui aiment bien pren­dre des pho­tos de trucs dans des musées et qui passent leur temps à tri­er les pho­tos une à une à la main par­mi les sous-caté­gories de « Caté­gorie regroupant les Air­bus A320 de la British Air­ways triés par aéro­port » et « Caté­gorie regroupant les couch­ers de soleil pho­tographiés depuis les plages de la région de Ker­ala ». Le pro­jet a raté le cap de la vidéo, celui de l’internationalisation, celui de la tran­si­tion vers les appareils mobiles, et je ne par­le même pas des médias inter­ac­t­ifs ou en trois dimen­sions, qui y sont com­plète­ment incon­nus. Il se mon­tre inca­pable d’accueillir con­ven­able­ment les con­tri­bu­tions de pro­fes­sion­nels et d’entreprises, ce qui représente une perte énorme. En bref, ce pro­jet a besoin d’une reprise en main et d’une feuille de route ; il faut qu’il con­sen­tisse des efforts pour diver­si­fi­er sa com­mu­nauté, pour s’organiser en suiv­ant les recom­man­da­tions de pro­fes­sion­nels, pour se dot­er d’outils con­tem­po­rains facil­i­tant la décou­verte, l’utilisation et le remix­age des œuvres hébergées. Sans cela, il restera sim­ple­ment une « galerie d’images pour Wikipé­dia », pas­sant à côté du rôle for­mi­da­ble qu’il pour­rait jouer en devenant la banque mul­ti­mé­dia uni­verselle du monde de l’éducation. Je lui souhaite de réalis­er tout cela cette année !

It’s hard to describe to oth­er peo­ple what it feels for me to lis­ten to Kei­th Jarrett’s music, because it sounds so mys­ti­cal. It’s sor­cery. When it final­ly works and the fire has been lit up, it is an open­ing of one­self, an immense lib­er­a­tion. I am pos­sessed by the music and pos­sess­ing it at the same time. It’s a con­nec­tion to some­thing greater that has been there all along, and the sud­den cer­tain­ty that every­thing so far that has led to this moment has been worth it. It’s a feel­ing a lit­tle like “telling the truth”. Whatever.

A thought­ful mem­ber wrote on the Kei­th Jar­rett dis­cus­sion group that all it takes is atten­tive lis­ten­ing to be tak­en to a dif­fer­ent place. To me, this is true only some of the time. I feel inescapably bound to mak­ing the music appear, some days I can effort­less­ly feed my mind many hours of it and some­times it takes months before I can again lis­ten to Jar­rett impro­vis­ing. It’s a strug­gle, what is record­ed in the audio file seems to be more like the key to some­thing with­in me for which I can’t always find the lock. After twen­ty years of lis­ten­ing I am still con­front­ed to this every time. If I am at the same time play­ing the piano in 1973 and being the entire audi­ence there and lis­ten­ing in my bed­room today, then why do I have so lit­tle com­mand over expe­ri­enc­ing this elevation?

Cer­tain­ly Jar­rett must have his own set of con­fronta­tions and con­flicts too. He is the ulti­mate link between all of us and some­thing beyond, and at the ori­gin of all those ephemer­al “man­i­fes­ta­tions”, for lack of a bet­ter word. But at the same time he is a pro­fes­sion­al per­former, expect­ed by every­one to pro­duce those on order in two-set events that are booked in advance. Lat­er, at com­mer­cial­ly sen­si­ble inter­vals, the mag­ic is pressed into shit­ty lit­tle rec­tan­gu­lar plas­tic box­es wrapped in card­board stamped with a brand of the largest and mean­est music cor­po­ra­tions of the planet.

I think Jarrett’s trou­bled rela­tion­ship with his audi­ences is sin­cere. I don’t believe he is arro­gant. I think the audi­ence and the impro­vi­sa­tion are parts of what makes it all work; that he is torn between want­i­ng to soar with all of us and being, time and time again, dis­ap­point­ed when he finds that two thou­sand humans are just as messy as every­one else could have pre­dict­ed. I saw him reject audi­ences in ways meant to hurt, and I pity him — if only he had Chick Corea’s or Hiro­mi Uehrara’s good spir­its! To make things worse, his rela­tion­ship to tech­nol­o­gy is super­sti­tious, and I find, ill-reflect­ed. But he is walk­ing on the crest of moun­tains, telling us of the oth­er side, and I read­i­ly believe the crest is real­ly sharp and treacherous.

I think of him with kind­ness. Jar­rett recent­ly suf­fered a stroke that left him unable to play. We, and espe­cial­ly him, are orphans now. I wish him well.

[updat­ed 2023-01-01]

If you are pay­ing rev­enue tax in Ger­many, the Ger­man fed­er­al gov­ern­ment can sup­port you finan­cial­ly with your dona­tions, in the form of reduc­tions in your rev­enue tax. The process is not par­tic­u­lar­ly com­pli­cat­ed, but not well doc­u­ment­ed in Eng­lish on the Inter­net. Here is how it works, based on my read­ings online, my under­stand­ing, and my own experience.

(I am not a lawyer. I share this infor­ma­tion in good faith. It may not be accu­rate.)

Which donations are eligible?

Dona­tions to non-prof­it orga­ni­za­tions work­ing for the pub­lic good in the Euro­pean Union are eli­gi­ble for tax deduc­tions in Ger­many. Either the orga­ni­za­tion is eli­gi­ble, or it is not; there is no grid or grad­u­a­tion. The gov­ern­ment must con­sid­er every dona­tion you declare for eli­gi­bil­i­ty; it may then accept or refuse them.

Mem­ber­ship fees to non-prof­it orga­ni­za­tions work­ing for the pub­lic good are con­sid­ered as a dona­tion. In gen­er­al, if you receive a dona­tion receipt from the receiv­ing orga­ni­za­tion, it is safe to assume the dona­tion is eli­gi­ble. If in doubt, con­tact the receiv­ing orga­ni­za­tion to check their eli­gi­bil­i­ty sta­tus with them.

How much help will you get?

The sum of your dona­tions is sub­tract­ed from your year­ly tax­able income. The dona­tions will there­fore result in a decrease in both your income tax (Lohn­s­teuer) and sol­i­dar­i­ty tax (Sol­i­dar­ität­szuschlag).

For rel­a­tive­ly small dona­tions (e.g. 100 euros), this means that the amount of help received from the Gov­ern­ment cor­re­sponds to your mar­gin­al tax rate (the tax rate at which the last 100 euros were earned). As a researcher in a pub­lic uni­ver­si­ty, my mar­gin­al tax rate reach­es up to about 35% when work­ing full-time. For my first dona­tion of 200 euros, I get approx­i­mate­ly 70 euros back as a tax deduction.

Deter­min­ing your mar­gin­al tax rate (Gren­zs­teuer­satz) is not par­tic­u­lar­ly easy. The Ger­man mar­gin­al tax rate depends on the tax­able income, an amount which is nei­ther indi­cat­ed in your pay slips, nor on your year­ly tax bul­letin (the Lohn­s­teuerbescheini­gung). The tax­able income (zu ver­s­teuern­des Einkom­men) is your gross income minus a num­ber of social con­tri­bu­tions (retire­ment pen­sions, social secu­ri­ty), minus a stan­dard thresh­old sum. As a researcher in a pub­lic uni­ver­si­ty, my tax­able income is close to 80% of my gross income when work­ing full-time.

The mar­gin­al tax rate varies con­tin­u­ous­ly with the tax­able income, which has two inter­est­ing con­se­quences. First, the more you earn, and the larg­er the amount of sup­port you receive from the gov­ern­ment. If your income varies with time, then it is in your inter­est to make those dona­tions on the years when you earn the most. Sec­ond, the more you donate, the small­er the amount of sup­port you receive (suc­ces­sive dona­tions are sub­tract­ed from slices of your income which are pro­gres­sive­ly less taxed, e.g. the first donat­ed 5000 euros were taxed at 35%, the next 5000 euros at 32%, and so forth). 

Ulti­mate­ly, dona­tions can only be deduct­ed up to 20% of your tax­able income for any one giv­en year. Dona­tions over that amount are car­ried for­ward to the fol­low­ing years with­out any lim­it in time (this process is automatic).

How is the deduction carried out in practice?

Wait until the fis­cal year is over. Dur­ing this time, your employ­er declares and pays your tax­es for you, assum­ing no dona­tions took place.

Once the year is over, con­nect to Elster, the Ger­man fed­er­al tax web­site. Note that your “Steuer­liche Iden­ti­fika­tion­snum­mer”, which is suf­fi­cient to login, is not your “Steuer­num­mer”, which is not always giv­en to you by the Ger­man admin­is­tra­tion. Car­ry out a mod­i­fi­ca­tion to your tax dec­la­ra­tion. Dona­tions are entered in the rubrics “zur Förderung steuer­begün­stigter Zwecke an Empfänger im Inland” and “zur Förderung steuer­begün­stigter Zwecke an Empfänger im EU- / EWR-Aus­land”.

For dona­tions pri­or to 2017, once your dec­la­ra­tion is com­plete, you must send the orig­i­nal dona­tion receipts to your local tax office (if you only send copies, they will write back ask­ing for the orig­i­nals). For all dona­tions over 200 euros, you must also sent a proof of pay­ment (e.g. an excerpt from a bank state­ment). A short let­ter with your per­son­al infor­ma­tion and a sen­tence sim­i­lar to “Anbei find­en Sie die Belege, die zu meinen Steuer­erk­lärun­gen für 2015 und 2016 gehören” suf­fices. In the case of dona­tions out­side of Ger­many, I like to include a short, half-page descrip­tion of the orga­ni­za­tion to which the dona­tion was made, to help offi­cials assess whether the orga­ni­za­tion qual­i­fies for a tax reduction.

For dona­tions made after Jan­u­ary 1st, 2017, you must be ready to send dona­tion receipts and proofs of pay­ment in case the tax office requests them. There is no oblig­a­tion to send those doc­u­ments spontaneously.

If your dona­tions exceed 20% of your tax­able income, the part of dona­tions beyond that amount (called the Verbleiben­der Zuwen­dungsvor­trag) is car­ried for­ward into the fol­low­ing years. The cal­cu­la­tion is car­ried out auto­mat­i­cal­ly by the fed­er­al tax office. The fol­low­ing year, you sim­ply need to check the tick box that says “Es wurde ein verbleiben­der Spenden­vor­trag fest­gestellt” in your declaration.

The Gov­ern­ment is prompt to act and will issue a refund, togeth­er with a com­plete tax bill sent by paper mail, with­in a few weeks fol­low­ing your dec­la­ra­tion. You can work on tax dec­la­ra­tions for the past five years, declar­ing any dona­tions for which you have kept receipts. The Ger­man gov­ern­ment will treat them equal­ly quick­ly, and even pro­vide inter­est on the refunds from for­mer years.

Conclusion

The sup­port pro­vid­ed by Ger­man gov­ern­ment when you make char­i­ta­ble dona­tions is real­ly sub­stan­tial. It is in prac­tice hard to pre­dict exact­ly the amount of sup­port you will receive. Nev­er­the­less, the amount of required paper­work is small. I hope this can encour­age you to increase dona­tions correspondingly!

In the sum­mer of 2020, I rent­ed a drone and took pho­tos and videos of Magde­burg, Ger­many. The pho­tos are now all pub­lished on Wiki­me­dia Com­mons and some serve to illus­trate Wikipedia arti­cles. I intend to use the videos as dec­o­ra­tive fea­tures in the videos of course in engi­neer­ing flu­id dynam­ics. In the mean­time, I pub­lish them here, under a CC-by license: this means you are free to use them for all pur­pos­es, includ­ing com­mer­cial pur­pos­es, as long as you cred­it me (Olivi­er Cley­nen).
It was a lot of fun play­ing with the drone, and cap­ture shots of my beloved city. The files linked here are 2160p H264 videos embed­ded in Matros­ka con­tain­ers, usu­al­ly less than a minute long.

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Now that the semes­ter is over, I can take a few moments to reflect over the 2020 edi­tion of my flu­id dynam­ics course at the Uni­ver­si­ty Otto von Guer­icke of Magde­burg.

The semes­ter began right as Ger­many shut down due to the pan­dem­ic cri­sis. The course, with 153 stu­dents, took place entire­ly online. I spent near­ly half of the semes­ter work­ing from abroad, attend­ing to a close rel­a­tive. I was nev­er able to meet any stu­dent physically.

The course pro­gressed on a week­ly basis. I released one chap­ter every week, a sin­gle PDF doc­u­ment con­tain­ing lec­ture notes and prob­lems. In the doc­u­ment, I linked to YouTube videos (on aver­age, five per chap­ter) where I cov­ered impor­tant ele­ments of the the­o­ry, and solved prob­lems step-by-step. I also linked to inter­est­ing illus­tra­tive videos. In week­ly, two-hour Zoom ses­sions, I answered any and all ques­tions that were thrown my way.

In addi­tion, every stu­dent received indi­vid­u­al­ized home­work as part of the peer-grad­ed home­work pro­gram I devel­oped with my col­leagues Math­ias Mag­dows­ki, Ger­mán San­ta-Maria and Jochen König. This year, par­tic­i­pa­tion in the home­work was manda­to­ry and count­ed 40% towards the final course grade. I hoped to run four instances of the home­work, but in the end, because of per­son­al mat­ters, only three pieces of home­work were hand­ed out.

A series of week­ly four-ques­tion quizzes, run through the University’s Moo­dle instance, added up to 10% of the final grade. The remain­ing 50% of the final grade con­sist­ed of the final two-hour invig­i­lat­ed exam­i­na­tion, with the same struc­ture (choose three prob­lems among five) as in for­mer years.

A lot has hap­pened through the semes­ter, and I have many mixed feel­ings about this edition.

First, I am glad I learned to record videos, and I think I got it right. A good-qual­i­ty, sub­ti­tled record­ing of a prob­lem being solved by hand (I used a Wacom tablet, an exter­nal micro­phone and an exter­nal web­cam plugged into a lap­top) is a much bet­ter tool to learn with than a live ses­sion in a class­room with a chalk­board. I chose YouTube as a com­pro­mise, because it suits stu­dents well, but will try to migrate to a Peer­Tube instance in the future.

Admin­is­tra­tive man­age­ment was a night­mare and cost me hours of work week­ly through­out the semes­ter. My uni­ver­si­ty does not com­mu­ni­cate well with either teach­ers or stu­dents —the local TV sta­tion knew of the revised semes­ter dates before I did— and pre­dictably the com­mu­ni­ca­tion between teach­ers and stu­dents is chaot­ic. Addi­tion­al­ly, my uni­ver­si­ty has no effec­tive con­trol over the course reg­is­tra­tion process: for exam­ple, just get­ting an up-to-date list of stu­dent emails is a chal­lenge. I hope bet­ter man­age­ment will alle­vi­ate me of that load in the future.

Com­mu­ni­ca­tion chan­nels between stu­dents remained out of my reach for the com­plete semes­ter. I heard What­sApp groups are the thing; in any case the Moo­dle dis­cus­sion boards of my course failed to reach crit­i­cal mass. Too many stu­dents address me direct­ly. I tried to redi­rect requests to the inter­ac­tive Zoom ses­sions and Moo­dle forums, but in the end I count only 174 Moo­dle posts, and 860 emails sent and received over the semes­ter (I do not count the 1800 mails processed auto­mat­i­cal­ly as part of the peer-grad­ed home­work pro­gram). An aver­age of 4.5 mails received, 4.5 sent every day is just too much for one class. A few stu­dents are dis­re­spect­ful (although always rev­er­ent), and many have com­plete­ly unre­al­is­tic expec­ta­tions, not hav­ing tru­ly real­ized what it means to be a sin­gle instruc­tor with 153 stu­dents on the side of research-relat­ed duties.

Zoom ses­sions went very well. The tech­ni­cal robust­ness of Zoom impressed me, espe­cial­ly in view of the low lev­el of com­put­er lit­er­a­cy and equip­ment of my stu­dents. Atten­dance (share of exam-goers present for 45 min­utes or more) began at 65%, decreas­ing lin­ear­ly with time down to 17% in the last ses­sion. I regret that so few stu­dents chose to turn on their cam­era, even though I respect their deci­sion. As a teacher, I yearn for visu­al con­tact and body lan­guage dur­ing inter­ac­tive ses­sions, but this semes­ter, I end­ed up star­ing most­ly at a wall of usernames.

One nice suc­cess was intro­duc­ing illus­tra­tions of peo­ple in the lec­ture notes, to pass across impor­tant points in para­graphs titled “advice from an expert”. I had some illus­tra­tions made to order, and licensed oth­ers under a lim­it­ed-use, com­mer­cial license, all fol­low­ing the advice of my col­league Dr. Kristin Hecht.

Those para­graphs had two pur­pos­es. First and fore­most, I am tired of flu­id mechan­ics being nar­rat­ed most­ly by old white men, and want­ed to put dif­fer­ent-look­ing peo­ple in charge of giv­ing tech­ni­cal advice to stu­dents. I hope my stu­dents, almost none of whom look like me, can iden­ti­fy them­selves with some of the per­sona dis­played in the lec­ture notes now. Sec­ond, using this tech­nique helped me with the tone of the lec­ture notes, which I had long found to be slight­ly bor­ing and too seri­ous. Now, I can keep the tech­ni­cal con­tent short and pre­cise, while indulging in a more relaxed tone on occa­sion, address­ing the read­er direct­ly. For good mea­sure, I also sprin­kled links to a few of my favorite sci­ence web­comics (such as xkcd) across the chapters.

The largest pain point remains the grad­ing. While the dis­tri­b­u­tion of final grades remains large­ly the same as in the last five years, there is a large dis­crep­an­cy between course­work and exam grades.
In the peer-grad­ed home­work pro­gram, there is evi­dence that a siz­able share of stu­dents par­tic­i­pat­ed in bad faith, which result­ed in low-qual­i­ty grad­ing of oth­er stu­dents. This is an inher­ent weak­ness of the pro­gram: if too many stu­dents, even when hand­ed a com­plete step-by-step worked-out guide, are unwill­ing or unable to iden­ti­fy the source of an error in the papers they grade, then they can­not be eas­i­ly “sort­ed out” of the sys­tem, and glob­al stu­dent moti­va­tion and learn­ing will suf­fer.
There is also plen­ty of evi­dence that the sys­tem of week­ly quizzes was abused. I had thought that because the stakes were low (quizzes amount to 10% of the final grade, so any one ques­tion weighs only 0,25%), there would be no incen­tive for gam­ing, and I was wrong.
Because of those issues, I went into the exam with the impres­sion that course­work grades did not reflect the true lev­el of learn­ing of a sig­nif­i­cant num­ber of stu­dents. The exam proved me right: with 55% of par­tic­i­pants fail­ing the exam prop­er, and 33% not even clear­ing a quar­ter of points, it was the worst stu­dent per­for­mance in record. This nec­es­sar­i­ly brings into ques­tion whether deploy­ing course­work is actu­al­ly worth the effort, since this year, it objec­tive­ly cor­re­lates with low­er learning.

There are many fac­tors that come into play here, not all of which are under my con­trol. First, this year the Uni­ver­si­ty lift­ed restric­tions on the num­ber of attempts allowed for each exam, and so some stu­dents may have been temped to have a “free try” (passed exams can­not be repeat­ed how­ev­er, which makes for weird dynam­ics). Sec­ond, grades secured with course­work reduce the pres­sure exert­ed on stu­dents dur­ing the exam. I have long under­stood that grades act as a met­ric for the student’s time bud­get­ing, both with­in my course and in between dif­fer­ent cours­es. This is com­plete­ly nat­ur­al, and I wouldn’t blame stu­dents for putting focus on oth­er exams where the stakes were high­er. (Prop­er qual­i­ty mea­sure­ment and man­age­ment would sub­stan­ti­ate those state­ments and help with strate­giz­ing, but unfor­tu­nate­ly, my uni­ver­si­ty is not there yet either.) And final­ly, the pan­dem­ic dis­pro­por­tion­ate­ly affect­ed stu­dents in my course, most of whom come from abroad. I can’t imag­ine what it means to work on an exam when you are barred from fly­ing back home to take care of loved ones, or uncer­tain whether you can even keep study­ing through the com­ing semester.

Look­ing ahead, I need to make the grades bet­ter reflect the lev­el of learn­ing. Quizzes won’t be grad­ed any­more, and I will like­ly make home­work an option­al, low-weight pro­gram again.
Ulti­mate­ly, it is clear that there are stu­dents in my course who have not attend­ed a sin­gle Zoom ses­sion dur­ing the semes­ter. There are stu­dents who do not think it use­ful to invest 20 min­utes watch­ing the exam prep video I sent them before mak­ing an attempt. There are stu­dents who are not able to manip­u­late a sim­ple equa­tion that con­tains only sym­bols, and there are stu­dents who have no inhi­bi­tion against writ­ing unin­ter­rupt­ed non­sense for two hours on a paper. Sure­ly, any of those last two issues pre­clude any suc­cess in an engi­neer­ing flu­id dynam­ics course. Before I make course­work a large part of the course again, I must be able to pre­vent those stu­dents from inter­fer­ing with the suc­cess of others.

I can­not con­clude this with­out men­tion­ing the sheer joy that comes out of all this work. It is uplift­ing and hum­bling now to meet stu­dents on cam­pus who took part in the course and express feed­back. This com­ing year, with most of the course con­tent now solid­ly cov­ered with 15-minute videos, I will be in a much bet­ter posi­tion to fol­low the foot­steps of my col­league Dr. Stef­fi Knorn and flip the course around. My vision is to be spend­ing all of my class time help­ing stu­dents actu­al­ly solve real­is­tic prob­lems in flu­id dynam­ics, using mod­ern tools and tech­niques. I look for­ward to 2021.

I own a city bicy­cle with a very nice 3‑speed Shi­mano Nexus 3 wheel hub. It is the SG-3C41 mod­el, which has an inte­grat­ed coast­er “backpedal” brake. (The SG-3R40 and SG-3D55 mod­els don’t have that.)

I real­ly dis­like coast­er brakes, which throw me off bal­ance when maneu­ver­ing at low speeds, make start­ing from a stand­ing posi­tion dif­fi­cult, and gen­er­al­ly dimin­ish my feel­ing of free­dom of move­ment when riding.

For­tu­nate­ly, it is pos­si­ble to deac­ti­vate the brake. It is an easy mod­i­fi­ca­tion, and it is com­plete­ly reversible. 

First, down­load the Inter 3 ser­vice man­u­al from the Shi­mano web­site. It is a very clear and com­plete doc­u­ment which shows you around the device, and also has a com­plete parts list.

Remove the wheel from the bicy­cle, and extract the hub from the wheel. It is safe to do so; the main roller bear­ings have their own cas­ings, so no bear­ing ball is at risk of falling off. There are two met­al brake pads inside the hub, held togeth­er by a sprung ring. They can be removed by hand.

After remov­ing the pads, you need to tight­en down the cen­trifu­gal­ly-expand­ing shaft unit around which the pads sat. The unit must be held togeth­er, to pre­vent it from expand­ing. A small piece of met­al wire will do the job, as shown in the pho­to below.

If you do not tight­en the expand­ing unit, the hub will work most­ly fine; how­ev­er, you will notice a small lag when engag­ing after free-wheel­ing. The lag also pops up when ped­al­ing con­tin­u­ous­ly at low-pow­er, cruis­ing speeds, and is ever so slight­ly annoy­ing. Tight­en­ing the expand­ing unit makes that dis­ap­pear entirely.

When reassem­bling the hub, you will need to tight­en two lock­ing nuts on the main shaft. The inner nut is only 3 mm thick, and is turned with a 22 mm key. Just like for any bicy­cle wheel hub, the two nuts must be tight­ened against one anoth­er at just the right posi­tion. Too close to the wheel, and the hub will not rotate nice­ly around the shaft; too far from the wheel, and the hub will move about slight­ly, even­tu­al­ly destroy­ing the roller bear­ings (I learned this the hard way so you don’t have to). There­fore, I high­ly rec­om­mend you use a flat 22-mm key to hold the inner nut, and then tight­en the nuts atten­tive­ly. Flat keys are very inex­pen­sive on Ebay.

Once every­thing is reassem­bled, the hub will work as before, except the rid­er can backpedal freely. There is no notice­able difference. 

The Inter 3 hub is a real­ly fine piece of engi­neer­ing. I must grant that it is not par­tic­u­lar­ly qui­et (the low­er gears are always free­wheel­ing rel­a­tive to the upper ones, so it it is only com­plete­ly silent in first gear). How­ev­er, the gears are staged just right for urban rid­ing, the ser­vice man­u­al is stel­lar, and, most impor­tant­ly, the gear switch­ing is flaw­less. Gears switch instant­ly, with­out ped­al move­ment, in a swift and sat­is­fy­ing turn of the wrist. I’ll nev­er go back.

The begin­nings of this mahogany desk from my dad’s house are not known for sure. The wood is very like­ly from Cuba, which is in itself a sad sto­ry, as this entire­ly renew­able resource was com­plete­ly wiped off from the region through cat­a­stroph­ic mis­man­age­ment. In any case, the desk arrived in the hands of a Sovi­et diplo­mat in the island.

The diplo­mat must have trav­eled around the world, and the desk land­ed in the Embassy of the USSR in Brus­sels, Bel­gium. The Embassy then donat­ed it to the Com­mu­nist Youth in Brus­sels. The orga­ni­za­tion shared its office with the Mai­son de Jeunes “1917” in the city, where my father worked in the six­ties and sev­en­ties. Pre­dictably, the occu­pants, a large group of young, loud, opin­ion­at­ed peo­ple with a knack for throw­ing par­ties and host­ing taste­ful live music, failed to take care of it prop­er­ly, and it fell into disrepair.

At some point, my father was asked to car­ry out elec­tric­i­ty cabling work in the Com­mu­nist Youth’s offices, where he spot­ted the desk. It was scratched, parts were miss­ing, and the leather cov­er was torn. An arrange­ment was made, my dad did the work for free and walked off with the desk.

At that time, my father was gath­er­ing old and inter­est­ing fur­ni­ture found in var­i­ous places, and learn­ing to restore them. Togeth­er with his part­ner at the time, he worked on the desk and they restored it com­plete­ly. He couldn’t find new draw­er han­dles to replace the miss­ing ones, so he had some forged based on the exist­ing ones at Sif­fleur in the city.

I was born in 1983. Short­ly after, he drove down to the French Riv­iera, found a job, and my moth­er and I joined him there, start­ing a new life. He brought all of his cher­ished fur­ni­ture with him, and so I have always known this desk, as well as half a dozen oth­er pieces of fur­ni­ture with sim­i­lar­ly inter­est­ing sto­ries. My dad always said that a good piece of wood­en fur­ni­ture was nicer to look at than a painting.

Last May, my dad lost all hope of recov­er­ing from of a long-term med­ical con­di­tion. At the time, the covid19 pan­dem­ic had just hit Europe, and my uni­ver­si­ty had just switched to online teach­ing, so I was able to work remote­ly. Some air­lines were oper­at­ing again, so I flew down south. I brought with me a half-decent lap­top, a web­cam, a micro­phone, and a Wacom tablet, all snapped off Ebay in the weeks prior. 

And so I arrived at the desk. Over the course of the fol­low­ing weeks, I was able to spend time with my dad in his last bat­tle, at home, all while work­ing: pro­duc­ing lec­ture videos, week­ly quizzes, indi­vid­u­al­ized peer-grad­ed home­work assign­ments, inter­ac­tive Zoom ses­sions, and most­ly-com­plete lec­ture notes for my course in flu­id dynam­ics. I had the oppor­tu­ni­ty to con­tem­plate and appre­ci­ate the many bless­ings which allowed me to be there. The sup­port of my super­vi­sor and col­leagues. The love of close rel­a­tives. The patience of stu­dents. The resilience of many tech­no­log­i­cal sys­tems upon which I depend­ed. And a blur­ry but strong inher­it­ed feel­ing for how to take life deci­sions and own­ing up to them. The desk was not par­tic­u­lar­ly com­fort­able, and I nev­er had time to fix the chair. But it was so fit­ting that I was able to work on this beau­ti­ful, sol­id, mas­sive-wood piece of my father’s life.

My father passed away in June. I flew back to Ger­many. I miss him. I don’t know what is going to hap­pen to the desk.

With uni­ver­si­ties mas­sive­ly turn­ing to online teach­ing, there is a lot of dis­cus­sion regard­ing exams, and pro­pos­als for tech-enabled, remote­ly proc­tored exam­i­na­tions are often prop­ping up.

I came across this deck of slides (archive) titled “Prü­fun­gen von zuhause aus? Geht das?” (“Exams from home? Is that pos­si­ble?”), authored in May 2019 by the cen­ter for teach­ing and learn­ing of the Teschnis­che Uni­ver­sität München (TUM). It is noth­ing short of horrifying.

There are only two instances of stu­dents in this TUM pre­sen­ta­tion: a smil­ing woman sit­ting on her bed, and a hand­ful of cheaters.

Sure­ly the author could have con­sid­ered the real­i­ty of going through an online proc­tored exam for the peo­ple who are at the heart of it: the students.

I am mild­ly nau­se­at­ed by this dis­cus­sion of var­i­ous deep sur­veil­lance tech­ni­cal sys­tems that some­how man­ages not to include a dis­cus­sion of ethics. Dump­ing it all on stu­dent con­sent is cheap and careless.

I’d care for a descrip­tion of the poten­tial for abuse, the risk of loss of con­trol of data, the lack of over­sight, and of the deep­er human right con­cerns asso­ci­at­ed with giv­ing a for-prof­it third par­ty access to the most inti­mate aspects of people’s lives. Drew Har­well cov­ers this well in the Wash­ing­ton Post this month: Mass school clo­sures in the wake of the coro­n­avirus are dri­ving a new wave of stu­dent sur­veil­lance.
After that we could per­haps dis­cuss the issue of fuel­ing deep dis­trust and con­tempt between teach­ers and learners.

Instead, in this deck of slides, we are shown a total­i­tar­i­an state’s dream sys­tem (face recog­ni­tion, eye move­ment track­ing, fin­ger­print­ing, type pat­tern analy­sis, remote stor­age of video record­ings, remote con­trol of per­son­al devices, you name it) with flow charts that have smi­leys in them.

It’s not flat­ter­ing for the TUM to release a doc­u­ment like this. We have ethics com­mit­tees for things as small as pace­mak­ers or ABS brak­ing sys­tems. Peo­ple of TUM. Think­ing of that was part of the actu­al homework.