dr. Aleš Mohorič [16355]

Polymer matrix tablets are an important drug-delivery system widely used for oral drug administration. Understanding the tablet hydration process, both experimentally and theoretically, is, thus, very important for the development of drug delivery systems that exhibit high drug loading capacity and controlled release potential. In this study, we used magnetic resonance microscopy (MRM) to nondestructively and dynamically analyze the water hydration process of xanthan-based tablets. The swelling process was characterized by well-resolved fronts of erosion, swelling, and penetration. The experimental results were complemented by numerical simulations of the polymer matrix hydration process. In the simulations, the polymer tablet matrix was modeled as an assembly of interacting chains with embedded drug particles, while its hydration process was mediated by interaction with solvent particles. The swelling dynamics were modeled within a Monte Carlo-based bond fluctuation model (BFM) that elegantly accounted for steric and nearest-neighbor interactions. This study provides an efficient experimental–theoretical approach for the study of polymer matrix swelling processes.

NMR pulse gradient spin echo is the most efficient method for non-invasive elucidation of molecular transport in heterogeneous media. With a proper interpretation of experimental data, the method can also be applied to investigate molecular self-diffusion in pores small enough that the characteristic diffusion times are much shorter than time, needed to build up the spin phase structure by the pulse of magnetic field gradient. This is demonstrated by the analysis of restricted self-diffusion measurement of water molecules trapped in a polyamide membrane. The results are presented as a distribution of spin-relaxation rates and pore sizes in this nanoporous system that also present the method in its true colors as a useful tool in the bio-nanotechology.

Polarni sij je pojav interakcije Sončevega vetra in Zemljine magnetosfere. Nastane, ko delci Sončevega vetra zaidejo v termosfero in vzbujajo zračne molekule. Opisane so lastnosti polarnega sija in mehanizem nastanka.

Sistem merskih enot mora biti notranje skladen, omogočati mora merjenje vseh fizikalnih količin, definicije osnovnih enot morajo temeljiti na naravnih konstantah in velikosti osnovnih enot se ne smejo spremeniti. To so bila osnovna vodila redefinicij osnovnih enot SI, ki nastopajo v veljavo maja 2019.

Zaznava gravitacijskih valov predstavlja pomemben mejnik v razvoju fizike, saj zaznamuje potrditev vseh napovedi teorije gravitacije. Dosežek je še toliko večji, ker je bilo od samega začetka jasno, da je odkritje zaradi šibkosti gravitacijske interakcije možno le ob doseganju občutljivosti, ki je omejena samo s Heisenbergovim načelom nedoločenosti. Trikratno odkritje zlitja dveh črnih lukenj na oddaljenosti milijarde svetlobnih let tako predstavlja hkrati truimf fizike črnih lukenj in temeljnih načel kvantne mehanike.

Detection of gravitational waves is an important milestone in the progression of physics, since it rounds up the list of all the predictions of theory of gravity. The achievement is all the greater because it was clear from the outset that the discovery, because of the weakness of the gravitational interaction, is only possible at a sensitivity on the limit of the Heisenberg principle of uncertainty. The three discoveries of a pair of merging black holes at a distance of billions of light years also represent the triumph of both physics of black holes and the fundamental principles of quantum mechanics.

Pandemija covid-19 je vplivala na učni proces, ki je bil v zaključku šolskega leta 2019/20 moten zaradi pouka na daljavo. Uspeh učnega procesa lahko merimo s testi znanja in posebej primerni so testi, katerih rezultate lahko primerjamo s predhodnimi generacijami in je njihova struktura ter izvedba neodvisna od razmer. Tak test je maturitetni izpit. Matura ima velik vpliv na možnost nadaljnjega izobraževanja, zato se je pojavil strah, da bo vpliv dela na daljavo zmanjšal njeno regularnost. Pomisleke o regularnosti izvedbe mature lahko ovržemo z analizo rezultatov mature in primerjavo z rezultati prejšnjih let.

Delovanje možganov je še vedno zavito v tančico skrivnosti. Nedavni napredki v slikanju z magnetno resonanco tančico nekoliko razgrinjajo. Difuzijsko uteženo slikanje z magnetno resonanco lahko razkrije lokalno anizotropijo difuzije in s tem potek živčnih vlaken. To je podatek na na mikroskopski skali, ki je manjša od ločljivosti slikanja samega.

Prispevek opisuje najpreprostejši model širjenja epidemije v populaciji. Opisane so glavne značilnosti modela in virusa ter primerjave z aktualno epidemijo virusa SARS-Cov-2.

Besedilo podaja kratko zgodovino odkrivanja gravitacijskih valov. Opisane so osnovne lastnosti valov in način detekcije. Uspešne detekcije valov kažejo na velik raziskovalni potencial gravitacijske astronomije.

The article outlines a short history of gravitational wave detection. Fundamental properties of waves and its detection are described. Recent successful detections show a great potential of gravitational astronomy.

Gravitacijski valovi so potujoče motnje v ukrivljenosti prostor-časa, ki jih ustvarjajo gibajoči objekti. Valovanje napove splošna teorija relativnosti. Prvič so ga izmerili leta 2015 z merilnim sistemom LIGO. Valovanje je nastalo ob združitvi dveh masivnih črnih lukenj, oddaljenih dobro milijardo svetlobnih let.

Gravitational waves are ripples in the curvature of space-time, caused by accelerated objects. Waves are described by general theory of relativity. The phenomenon was succesfully directly detected for the first time in 2015 with the measuring system LIGO. The detected waves were the result of two black holes merger more than a billion light-years ago.

V članku so predstavljeni človeški barvni vid, osnove barvnih sistemov in način, kako prikažemo barvo določenega svetlobnega spektra z dostopno programsko opremo.

The article describes human color vision, basics of color systems and a way of repre- senting color of a light with a given spectrum by readily available software.

V letu 2015 sta Nobelovo nagrado za fiziko prejela Takaaki Kajita z univerze v Tokiju, Japonska, in Arthur B. McDonald s Kraljeve univerze v Kingstonu, Kanada, za pomembno vlogo v eksperimentih Super-Kamiokande in SNO, ki nedvoumno kažeta na to, da nevtrini ene vrste prehajajo v nevtrine druge vrste in nazaj. Prehodi, ki jih imenujemo nevtrinske oscilacije, so možni le, če imajo nevtrini maso. To odkritje je spremenilo naše razumevanje temeljev narave in lahko pomembno vpliva na fizikalni pogled na vesolje.

This year's (2015) Nobel Prize in physics was awarded to Takaaki Kajita, University of Tokyo, Japan, and to Arthur B. McDonald, Queen's University, Kingston, Canada, for their key contributions to the experiments which demonstrated that neutrinos change identities. This metamorphosis requires that neutrinos have mass. The discovery has changed our understanding for innermost workings of matter and can prove cruical to our view to the universe.

Žarnica sveti zato, ker v njej električni tok drobno kovinsko žico segreje do zelo visoke temperature. Svetilnost žarnice, priključene na izmenično napetost, niha z dvojno frekvenco toka in zaostaja v fazi za trenutno električno močjo zaradi omejenega toplotnega toka in toplotne kapacitete žareče žice.

An incandescent bulb radiates light because electric current heats up its filament to a very high temperature. The luminosity of an incandescent lamp driven by AC oscillates at double frequency of the current and is out of phase with the electric power supplied because of the finite heat capacity of the filament and the limited rate at which it radiates heat.

Prispevek opisuje preprost model naravne konvekcije v valjasti geometriji. Reševanja sklopljenega sistema sistema diferencialnih enačb, ki opisujejo gibanje in toplotne tokove tekočine, se lotimo s Fourierjevo metodo in obdržimo čim manj členov. Rešitve poenostavljenega sistema v faynem prostoru težijo k Lorenzovem atraktorju, če je temperaturni gradient dovolj velik. Rešitve, ki jih poiščemo numerično, dajo občutek za temperaturne gradiente, velikosti tokov in časovno skalo, na kateri pride do sprememb.

The article describes a basic model of natural convection in cylindrical geometry. We solve the coupled system of dynamical and thermodynamical equations describing a liquid by truncating the Fourier series. The solutions of the simplified system tend toward the Lorenz attractor in phase space for large enough temperature gradients. The numerical solutions offer an insight into the order of temperature, flow, and characteristic time, typical for convection in a closed container.

Pred štiristo leti se je Galilej lotil opazovanaj nočnega neba s teleskopom. Pri tem je odkril štiri največje Jupitrove lune. Opazovanje gibanja lun je pomembno prispevalo k razvoju heliocentričnega sistema in k spoznanju o končni hitrosti svetlobe. Opayovanja Jupitrovih lun se s preprostimi sodobnimi pripomočki lahko lotimo tudi sami.

Four hundred years ago Galileo observed the night skies with a telescope. He discovered the four largest moons of Jupiter. The motion of the moons contributed to advent of the heliocentric system and recognition of the finite speed of light. The observation of the Jovian satellites can be done at home with the use of some simple modern utilities.

Sprejemnost tuljave je definirana funkcija kraja, ki pove, kolikšen signal inducira v tuljavi magnetni dipol, ki precesira okoli neke osi na nekem mestu. Tu je pokazan račun za tuljavo, ki ima obliko krožne zanke. Izračunan je tudi signal, ki ga v taki zanki inducira neskončno dolg valjast vzorec istega premera, kot je premer zanke.

The sensitivity of the coil is a function of position given as a normalized signal induced by a magnetic dipole precessing in a given position round a certain axis. Here, the sensitivity of a circular loopis presented. The signal, induced by an infinite uniformly magnetized cylindrical rod, with the same diameter as the loop, is calculated as an example of the use of sensitivity

The question about the proper stohastic treatment of the spin-echo self-diffusion attenuation of confined particle that arises when short gradient pulse approximation fails is still open. In the following article we compare results of computer simulation of the spin-echo spatial distribution with the theoretical calculations for the PGSE sequence with long gradient pulses. For the sake of simplicity we investigate restricted self-diffusion for one-dimensional problem where the spin-bearing particles are trapped parallel perfectly reflecting planes and with gradient applied normal to the planes. Computer simulation of Brownian motion of the spins in confined space is implemented as numerical simulation of successive random steps, which are restricted to the space between two perfectly reflecting parallel planes. The spatial distribution of the spin-echo signal is calculated from the simulated trajectories when the magnetic field gradient is perpendicular to the plane boundaries. Theoretical calculation by the method of cumulant expansion in the Gaussian approximation (cumulants higher than second are negligible), where the Einstein's approximation of the VCF (hsort time VCF) is used, agreeswith the results of the simulation only for the particle displacement shorter than the size of the confinement. For a long gradient sequence, when the number of collisions between spins and walls increases, this approximation shows a strong deviation from the result of the simulation. Replacement of the short time VCF with the Oppenheim and Mazur solution gives a better approximation to the results of simulation. To get even closer fit tothe simulated signal we have made simple value estimation for cumulants higher than the second. It points out that for a long gradient sequence we should considered higher orders of cumulants for the proper treatment of restricted self-diffusion in an isolated pore.

Ob 70-letnici DMFA Slovenije je bila 27. in 28. septembra 2019 na Bledu organizirana 1. mednarodna konferenca o poučevanju matematike, fizike in astronomije z vodilno temo delo z nadarjenimi učenci (tekmovanja, krožki, tabori, raziskovalne naloge…).

Učbenik za fiziko za gimnazije in srednje šole