Mechanics Colloquium

 

PROGRAM

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MATEMATIČKI INSTITUT SANU
ODELJENJE ZA MEHANIKU

PROGRAM ZA FEBRUAR 2023.

 

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Predavanja se mogu pratiti na daljinu preko stranice:
https://miteam.mi.sanu.ac.rs/asset/YfY2cZTcN3YwGqFjc
Ukoliko želite da učestvujete u radu seminara ili da postavite pitanja na kraju predavanja, a još niste registrovani na miteam platformi Matematičkog instituta, možete se registrovati popunjavanjem forme:
https://miteam.mi.sanu.ac.rs/asset/o9cuDZYqrq7jvFxw8
Arhiva snimljenih predavanja se nalazi na stranici:
https://miteam.mi.sanu.ac.rs/asset/j9rAJJvBQHx2zgSSH

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Pozivamo Vas da učestvujete u radu sednica Odeljenja i to:

Sreda, 08.02.2023. u 18:00, Online
M. Ćosić i M. Hadžijojić, Institut za nuklearne nauke Vinča
KOMPLEKSNOST BOMOVIH TRAJEKTORIJA POZITONA U HIRALNIM NANOCEVIMA
U ovom seminaru biće predstavljeni rezultati studije dinamike 1-MeV pozitrona kanalisanih kroz kratke jednozide ugljenične nanocevi hiralnog indeksa (11, 9). Potencijalna energija međudejstva pozitron-nanocev dobijena je podužnim usrednjavanjem potencijala međudejstva pozitrona i atoma ugljenika. U klasičnom pristupu, razmatrane su prostorne i ugaone funkcije transmisije i njima odgovarajuće raspodele kanalisanih čestica za razne dužine nanocevii. Ispitana je veza kritičnih tačaka uvedenih preslikavanja sa kaustikama i duginim maksimuma raspodela. U kvantnom pristupu dinamika je dobijena rešavanjem jedno-dimenzionalne vremenski-zavisne Šredingerove jednačine, pri čemu su u početnom trenutku pozitroni bili predstavljeni Gausovim tlasnim paketom velike varijanse. Uočeno je postojanje većeg broja singulariteta faze talasne funkcije pozitrona – tj. mesta gde je gustina verovatnoće nalaženja pozitrona jednaka nuli – čija se raspodela usložnjava sa dužinom nanocevi. Posebna pažnja je posvećena vezi singulariteta faze sa lokalnim LJapunovim eksponentima kratkog vremena Bomovih trajektorija. Pokazano je da interakcija singulariteta i Bomovih trajektorija dovodi do pozitivnog globalnog LJapunovom eksponenta što čini dinamiku Bomovih trajektorija kompleksnom.

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Sreda, 22.02.2023. u 18:00, Online
Fedor Mesinger, Serbian Academy of Sciences and Arts
WEATHER PREDICTION AS A NUMERICAL INTEGRATION PROBLEM: HISTORY, CHALLENGES, AND SKILL OF THE ETA MODEL
It is now a little more than 200 years that the Navier-Stokes fluid motion equations are known, but only about 120 years since the possibility was pointed out and necessary tasks specified in integrating these equations to predict weather. But with weather, the situation is not the same as in numerical integration of hyperbolic partial differential equations. While we have an initial and boundary conditions problem, neither of those can be precisely known. For example, the required initial condition can be known only approximately, with errors. If we even so generate an analysis to obtain the initial values of our time dependent variables, wind, temperature, more, at points of a grid, what do these values represent?
While the first successful integration of an atmospheric fluid dynamics equation, the vorticity equation, was published in 1950, only about two decades later practically useful results began to be achieved. They werearrived at using what is referred to as primitive equations, equations obtained by calculating vertical velocity using the two horizontal components. Among the first primitive equation codes for a limited area model was one I wrote in Belgrade during the winter break of 1973, a forerunner of what later became referred to as the Eta model. With later upgrades, primarily those of the eta vertical coordinate I added in 1984, and Zaviša Janjić's transformation of Akio Arakawa horizontal advection scheme to the model's semi-staggered grid, both implemented at the U.S. Weather Service at about the same time, it performed better than any of several regional models that service was at the time running. Eventually, in 1993, the Eta was officially accepted as the principal U.S. regional prediction model. It remained in that capacity until mid 2006.
Lately, the Eta is extensively used also as a regional climate model (RCM), mostly over the South American domain, and in near-real time for the North American Regional Reanalysis (NARR), run by the U.S. National Centers for Environmental Prediction.
After the “freezing” of its code at the end of the nineties to be used for NARR, two significant upgrades of its “dynamical core” were implemented. As an illustration of its resulting skill ensemble forecasts of the position of the upper-tropospheric jet stream are shown, compared to those of its driver highly acclaimed European Centre for Medium Range Forecasts (ECMWF) model.

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Obavezno je nošenje maski i održavanje distance. Broj prisutnih na predavanju ograničen na najviše 10 (uključujući i predavača).

Predavanja su namenjena širokom krugu slušalaca, uključujući studente redovnih i doktorskih studija. Održavaju se sredom sa početkom u 18 sati u sali 301f na trećem spratu zgrade Matematičkog instituta SANU, Knez Mihailova 36.

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