Dynamical screening of the Coulomb interaction for two confined electrons in a magnetic field

We show that a difference in time scales of vertical and lateral dynamics permits one to analyze the problem of interacting electrons confined in an axially symmetric three-dimensional potential with a lateral oscillator confinement by means of the effective two-dimensional Hamiltonian with a screened Coulomb interaction. Using an adiabatic approximation based on action-angle variables, we present solutions for the effective charge of the Coulomb interaction (screening) for a vertical confinement potential simulated by parabolic, square, and triangular wells. While for the parabolic potential the solution for the effective charge is given in a closed anlytical form, for the other cases similar solutions can be easily calculated numerically.Comment: 10 pages, 6 figure

The language of dialogue in the Arabic novel ; Язык диалога в арабском романе

Sve do savremene epohe, pridržavanje normi „božanskog“ i „božanstvenog“ arapskog jezika presuđivalo je statusu književnog dela i njegovom pripajanju zvaničnom arhivu kulturnih uzora. Dela popularne i narodne književnosti istisnuta su iz ove reprezentativne riznice zbog prisustva nestandardnih varijeteta u njihovom sastavu. Dati lingvistički kriterijum u selekciji tekstova učinio je elitnu književnost jednim od najvažnijih svetovnih bastiona čistog, ispravnog, rečitog arapskog koda – fushe, ali i paravanom koji je prikrivao slojevitu jezičku stvarnost arapske govorne zajednice. Krajem XIX veka, lingvističke „pregrade” između pomenutih tipova književnosti relativizovane su pod uticajem savremenog lingvističkog pristupa, koji se temelji na posmatranju jezika kao evolutivnog bića. Tome je, zatim, doprineo uticaj književno-jezičkih principa iz zapadne književnosti, koju su arapski pisci počeli da prevode i oponašaju. Jezički preobražaj najpre je postao osetan u novim formama pripovedačke proze – drami, priči i romanu, dok su se arabljanski poetski kanoni, u okviru kojih se fusha podrazumevala kao jedino validno sredstvo izraza, zadržali sve do početka XX veka...Until the contemporary era, the adherence to the norms of the “celestial” and “divine” Arabic language served as the final verdict on the status of a literary work and its inclusion into the offical archive of cultural models. The works of popular and folk literature were ousted from this representative treasury due to the presence of non-standard varieties in their texts. The given linguistic criterion in the textual selection made elite literature one of the staunchest secular bastions of the pure, correct, eloquent Arabic code – the Fusha, but also a screen that concealed a multi-layered linguistic reality of the Arabic-speaking community. In the late 19th century, the linguistic “barriers” between the above-mentioned types of literature were relativised under the influence of the contemporary linguistic approach, based on the observation of language as an entity prone to evolutionary change. Its cause was, thereafter, supported by literary-linguistic principles from Western literature, which Arabic authors engaged in translating and imitating. The language change was first felt in the new forms of narrative – the drama, the short story and the novel, whereas the Arabic poetic canons, within which the Fusha was taken for granted as the only valid means of expression, were preserved all until the early 20th century..

A geometrical crossover in excited states of two-electron quantum dots in a magnetic field

We use the entanglement measure to study the evolution of quantum correlations in two-electron axially-symmetric parabolic quantum dots under a perpendicular magnetic field. We found that the entanglement indicates on the shape transition in the density distribution of two electrons in the lowest state with zero angular momentum projection at the specific value of the applied magnetic field.Facultad de Ciencias Exacta

A geometrical crossover in excited states of two-electron quantum dots in a magnetic field

We use the entanglement measure to study the evolution of quantum correlations in two-electron axially-symmetric parabolic quantum dots under a perpendicular magnetic field. We found that the entanglement indicates on the shape transition in the density distribution of two electrons in the lowest state with zero angular momentum projection at the specific value of the applied magnetic field.Facultad de Ciencias Exacta

On analytical solutions of f(R) modified gravity theories in FLRW cosmologies

A novel analytical method for f(R) modified theories without matter in Friedmann-Lemaitre-Robertson-Walker spacetimes is introduced. The equation of motion for the scale factor in terms of cosmic time is reduced to the equation for the evolution of the Ricci scalar R with the Hubble parameter H. The solution of equation of motion for actions of the form of power law in Ricci scalar R, is presented with a detailed elaboration of the action quadratic in R. The reverse use of the introduced method is exemplified in finding functional forms f(R) which lead to specified scale factor functions. The analytical solutions are corroborated by numerical calculations with excellent agreement. Possible further applications to the phases of inflationary expansion and late-time acceleration as well as f(R) theories with radiation are outlined.Comment: 16 pages, 6 figures. v2: minor changes, references added. v3: minor changes, more references added. v4: version to appear in IJMPD. v5: DOI and journal reference adde

Silencing of germacrene A synthase genes reduces guaianolide oxalate content in <i>Cichorium intybus</i> L.

Chicory (Cichorium intybus L.) is a medicinal and industrial plant from the Asteraceae family that produces a variety of sesquiterpene lactones (STLs), most importantly bitter guaianolides: lactucin, lactucopicrin and 8-deoxylactucin as well as their modified forms such as oxalates. These compounds have medicinal properties; however, they also hamper the extraction of inulin – a very important food industry product from chicory roots. The first step in guaianolide biosynthesis is catalyzed by germacrene A synthase (GAS) which in chicory exists in two isoforms – GAS long (encoded by CiGASlo) and GAS short (encoded by CiGASsh). AmiRNA silencing was used to obtain plants with reduced GAS gene expression and level of downstream metabolites, guaianolide-15-oxalates, as the major STLs in chicory. This approach could be beneficial for engineering new chicory varieties with varying STL content, and especially varieties with reduced bitter compounds more suitable for inulin production

Bragg diffraction of large organic molecules

We demonstrate Bragg diffraction of the antibiotic ciprofloxacin and the dye molecule phthalocyanine at a thick optical grating. The observed patterns show a single dominant diffraction order with the expected dependence on the incidence angle as well as oscillating population transfer between the undiffracted and diffracted beams. We achieve an equal-amplitude splitting of $14 \hbar k$ (photon momenta) and maximum momentum transfer of $18 \hbar k$. This paves the way for efficient, large-momentum beam splitters and mirrors for hot and complex molecules.Comment: 8 pages, 7 figures (including Supplemental Material). Corrected errors in bibliograph

Khronon inflation

We study the possibility that the approximate time shift symmetry during inflation is promoted to the full invariance under time reparametrization t \to \tilde t(t), or equivalently under field redefinition of the inflaton \phi \to \tilde\phi(\phi). The symmetry allows only two operators at leading order in derivatives, so that all n-point functions of scalar perturbations are fixed in terms of the power spectrum normalization and the speed of sound. During inflation the decaying mode only decays as 1/a and this opens up the possibility to violate some of the consistency relations in the squeezed limit, although this violation is suppressed by the (small) breaking of the field reparametrization symmetry. In particular one can get terms in the 3-point function that are only suppressed by 1/k_L in the squeezed limit k_L \to 0 compared to the local shape.Comment: 15 pages, 1 figure, v2. changes regarding the violation of the consistency relation. JCAP published versio

Threshold Laws for the Break-up of Atomic Particles into Several Charged Fragments

The processes with three or more charged particles in the final state exhibit particular threshold behavior, as inferred by the famous Wannier law for (2e + ion) system. We formulate a general solution which determines the threshold behavior of the cross section for multiple fragmentation. Applications to several systems of particular importance with three, four and five leptons (electrons and positrons) in the field of charged core; and two pairs of identical particles with opposite charges are presented. New threshold exponents for these systems are predicted, while some previously suggested threshold laws are revised.Comment: 40 pages, Revtex, scheduled for the July issue of Phys.Rev.A (1998