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Glej tudi: Obvestila, novice, ...
Ce zelite, da bi bili seminarji vasega odseka objavljeni na spletnih straneh Instituta "Jozef Stefan", nas prosim obvestite po e-mailu.
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Povzetek: Masa osnovnih gradnikov vesolja - kvarkov, elektronov in elekronom podobnih delcev - je osnovnega pomena pri razvoju vesolja od njegovega stvarjenja z velikim pokom naprej in v veliki meri doloca svet, v katerem zivimo. Izvor mase je trenutno najvecja bela lisa na sicer natancnem zemljevidu Standardnega Modela, s katerim fiziki na pragu 21. stoletja opisujemo osnovne gradnike snovi in sile med njimi. Najbolj elegantno resitev ponuja hipoteza o spontanem zlomu simetrije, ko delci dobijo maso ob sklopitvi s Higgsovim poljem. Ce je hipoteza pravilna, je vesolje v prvih trenutkih po velikem poku vsebovalo tudi mnozico delcev, ki jih menujemo Higgsovi bozoni. Sveze novice iz Evropskega laboratorija za fiziko delcev CERN pri Zenevi kazejo na moznost, da se je fizikom s trkalniki posrecilo ustvariti pogoje za ponovno tvorbo hipoteticnih Higgsovih delcev. Ocenili bomo verjetnost, da gre pri izmerjenih procesih res za nastanek in razpad Higgsovih bozonov in s tem za potrditev domneve o spontanem zlomu simetrije, prav tako pa bomo poskusili uganiti nadaljni potek zgodbe o izvoru mase. Vabljeni! |
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Povzetek: Molecular recognition leading to Watson-Crick hybridization between complementary DNA oligonucleotides is the basis of DNA computation [1], of self-assembly schemes that use DNA as 'addressable glue' [2] and of DNA nanostructure fabrication [3]. We report the construction of a new class of active nanostructure: a machine in which DNA is used not only as a structural material but also as a fuel [4]. The machine, which has the form of a pair of tweezers, consists of two DNA duplexes linked by a flexible hinge of single-stranded DNA. It may be repeatedly closed and opened by sequential addition of 'fuel' and 'removal' strands of DNA; operation of the machine alters the separation of dye molecules on the ends of the tweezer arms on a nanometre length scale. We also demonstrate kinetic control of DNA hybridization: 1) hybridization is topologically inhibited by formation of a loop complex with a protective strand; 2) a DNA catalyst promotes hybridization by partially displacing the protective strand and opening the loop. These results suggest the possibility of using cooperative interactions to control non-equilibrium self-assembly, a generalization of conventional equilibrium self-assembly strategies with important implications for the design of DNA computers and for the fabrication of nanometre-scale devices. [1] L. M. Adleman, Science 266, 1021 (1994) |