IJS KOLOKVIJ, sreda 10. 4. 2019, ob 13.00 uri, prof. dr. Matthias Sperl

[Natasa Gosevac]

Vabimo vas na 15. predavanje iz sklopa "Kolokviji na IJS" v letu 2018/19, ki
bo v sredo, 10. aprila 2019, ob 13 uri v Veliki predavalnici Instituta
>Jožef Stefan<  na Jamovi cesti 39 v Ljubljani. Napovednik predavanja
najdete tudi na naslovu http://www.ijs.si/ijsw/Koledar_prireditev, posnetke
preteklih predavanj pa na http://videolectures.net/kolokviji_ijs. 

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~



prof. dr. Matthias Sperl

Deutsches Zentrum für Luft- und Raumfahrt, Köln, Nemčija

 

Idealna stanja granularnih snovi v vesolju

Takoj za vodo so granularne snovi najbolj uporabljani materiali ali snovna
stanja v industriji. Kljub tehniškemu pomenu se raziskav fizikalnih osnov
granularnih snovi lotevamo šele v zadnjem času. Glavna ovira pri opisu
granularnih snovi s statistično fiziko je močan vpliv neravnovesne dinamike:
zaradi izgube energije se že pri trku dveh delcev zlomi simetrija na obrat
časa, tako da so granularne snovi izven ravnovesja in s tem teoretični in
eksperimentalni izziv. 

Poleg tega so granularne snovi z različnimi gostotami zelo občutljive za
vpliv težnosti. Zato je izvajanje eksperimentov v mikrogravitaciji cesto
koristno ali celo nujno: na Zemlji se granularni plini hitro sedimentirajo,
granularne kapljevine so močno anizotropne, v granularnih skladih pa imamo
velike gradiente tlaka. V vseh naštetih stanjih nudijo eksperimenti na
platformah kot so parabolični let, stolp za prosti pad, raziskovalne rakete
in Mednarodna vesoljska postaja vpogled v obnašanje v idealnih ansamblov v
mikrogravitaciji, kjer lahko granularne pline vzbujamo homogeno, granularne
kapljevine opazujemo v izotropnih okoliščinah in granularne trdnine
raziskujemo brez gradientov.

Za karakterizacijo teh idealnih stanj uporabljamo vrsto diagnostičnih
pristopov od videa, sipanja svetlobe, rentgenske radiografije, dvolomnosti
zaradi mehaničnih napetosti do širjenja zvoka. V predavanju bomo orisali,
kako lahko rezultati tovrstnih eksperimentov nudijo vpogled v obnašanje
granularnih snovi in prispevajo k globljemu razumevanju.

Predavanje bo v angleščini.

Lepo vabljeni!

 

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We invite you to the 15th Institute colloquium in the academic year 2018/19.
The colloquium will be held on Wednesday, April 10, 2019 at 13 PM in the
main Institute lecture hall, Jamova 39, Ljubljana. To read the abstract
click   <http://www.ijs.si/ijsw/Koledar_prireditev>
http://www.ijs.si/ijsw/Koledar_prireditev. Past colloquia are posted on
<http://videolectures.net/kolokviji_ijs>
http://videolectures.net/kolokviji_ijs.

********************************************

prof. dr. Matthias Sperl

Deutsches Zentrum für Luft- und Raumfahrt, Köln, Germany

 

 

Ideal states of granular matter in space

 

Second only to water in volume, granular matter is the most frequently used
material or material state in industry. Despite its importance in
engineering, many physical foundations of granular matter are only now being
investigated. A major obstacle to describe granular matter within
statistical physics is the strong influence of out-of-equilibrium dynamics:
Already the two-particle collision breaks time-reversal symmetry due to
energy loss and renders granular systems out-of-equilibrium and thus a
challenge in theory and experiment alike.

In addition, granular matter at different densities is strongly susceptible
to the influence of gravity. Hence, experiments require and can benefit from
experiments in microgravity: On ground, granular gases sediment quickly,
agitated granular fluids are strongly anisotropic, and granular packings
exhibit large gradients in pressure. For all three of those states,
experiments on several platforms such as parabolic flight, drop tower,
sounding rocket and International Space Station demonstrate access to unique
and ideal ensembles under microgravity. Granular gases can be agitated
homogeneously, granular fluids observed under isotropic conditions, and
granular solids monitored free of gradients. 

In order to characterize those ideal states a variety of diagnostics can be
applied: video imaging, light-scattering, X-ray radiography, stress
birefringence, and sound  transmission. A synopsis shall be given how the
results from these experiments provide  valuable insights into the behavior
of granular matter and contribute to a deeper understanding. 

 

Cordially invited!

 

 

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