Lattice dynamics effects on small polaron properties

This study details the conditions under which strong-coupling perturbation theory can be applied to the molecular crystal model, a fundamental theoretical tool for analysis of the polaron properties. I show that lattice dimensionality and intermolecular forces play a key role in imposing constraints on the applicability of the perturbative approach. The polaron effective mass has been computed in different regimes ranging from the fully antiadiabatic to the fully adiabatic. The polaron masses become essentially dimension independent for sufficiently strong intermolecular coupling strengths and converge to much lower values than those tradition-ally obtained in small-polaron theory. I find evidence for a self-trapping transition in a moderately adiabatic regime at an electron-phonon coupling value of .3. Our results point to a substantial independence of the self-trapping event on dimensionality.Comment: 8 pages, 5 figure

Different classes of genomic inserts contribute to human antibody diversity

Recombination of antibody genes in B cells can involve distant genomic loci and contribute a foreign antigen-binding element to form hybrid antibodies with broad reactivity for Plasmodium falciparum. So far, antibodies containing the extracellular domain of the LAIR1 and LILRB1 receptors represent unique examples of cross-chromosomal antibody diversification. Here, we devise a technique to profile non-VDJ elements from distant genes in antibody transcripts. Independent of the preexposure of donors to malaria parasites, non-VDJ inserts were detected in 80% of individuals at frequencies of 1 in 10(4) to 10(5) B cells. We detected insertions in heavy, but not in light chain or T cell receptor transcripts. We classify the insertions into four types depending on the insert origin and destination: 1) mitochondrial and 2) nuclear DNA inserts integrated at VDJ junctions; 3) inserts originating from telomere proximal genes; and 4) fragile sites incorporated between J-to-constant junctions. The latter class of inserts was exclusively found in memory and in in vitro activated B cells, while all other classes were already detected in naïve B cells. More than 10% of inserts preserved the reading frame, including transcripts with signs of antigen-driven affinity maturation. Collectively, our study unravels a mechanism of antibody diversification that is layered on the classical V(D)J and switch recombination

Phase diagram of the Holstein polaron in one dimension

The behavior of the 1D Holstein polaron is described, with emphasis on lattice coarsening effects, by distinguishing between adiabatic and nonadiabatic contributions to the local correlations and dispersion properties. The original and unifying systematization of the crossovers between the different polaron behaviors, usually considered in the literature, is obtained in terms of quantum to classical, weak coupling to strong coupling, adiabatic to nonadiabatic, itinerant to self-trapped polarons and large to small polarons. It is argued that the relationship between various aspects of polaron states can be specified by five regimes: the weak-coupling regime, the regime of large adiabatic polarons, the regime of small adiabatic polarons, the regime of small nonadiabatic (Lang-Firsov) polarons, and the transitory regime of small pinned polarons for which the adiabatic and nonadiabatic contributions are inextricably mixed in the polaron dispersion properties. The crossovers between these five regimes are positioned in the parameter space of the Holstein Hamiltonian.Comment: 19 pages, 9 figure

Spinodally decomposed patterns in rapidly quenched Co-Cu melts

The Co-Cu system is analyzed in the region of metastable miscibility gap with separation of the undercooled melt into Co-rich and Cu-rich liquids [1]. Phase separation of undercooled and quenched samples of Co50Cu50 melt are investigated experimentally using electromagnetic levitation (EML) technique, quenching the undercooled melt onto a Pb-solder coated copper chill substrate and by splat quenching methods. It is found that quenching of the liquid samples with cooling rates of 106-107 K/s leads to a frozen in microstructure of spinodally decomposed liquids. The composition of the Co-rich phase measured by TEM-EDS is Co71.7Cu28.3 and that of the Cu-rich phase is Co26.8Cu73.2. These compositions are inside the spinodal region and close to the calculated spinodal boundary in the phase diagram of the Co-Cu system. The spinodally separated samples have periodicity of mean distance between patterns of about 0.12-0.4 μm. Using the model of fast spinodal decomposition (see Ref. [2] and references therein), computational modelling is carried out using semi-implicit numeric scheme as described in Ref. [3]. The results of modelling confirm the ability to quantitatively reproduce experimentally frozen spinodal patterns by their periodicity. The calculated time for the complete phase separation into the Co-rich and Cu-rich phases (in evolution spinodally decomposing patterns) is greater than the time for samples solidifying at cooling rates of 106-107 K/s. References [1] M. Kolbe, C.D. Cao, X.Y. Lu, P.K. Galenko, B. Wei, D.M. Herlach, Materials Science and Engineering A 375-377, 520 (2004). [2] P. Galenko, D. Jou, Physica A 388, 3113 (2009). [3] N. Lecoq, H. Zapolsky, P. Galenko, The European Physical Journal ST 177 165 (2009)