The manufacture of antibodies in vitro

A protein solution with the properties of a specific antiserum to the triphenylmethane dye methyl blue has been made by treating a solution of bovine gamma-globulin and the dye with alkali and then slowly neutralizing the alkali. Some success has been obtained also in the formation of antibodies from other serum proteins and by other denaturation-renaturation procedures. By heating solutions of gamma-globulin and antigen to 57°C. for several days antisera homologous to the antigens have been prepared. This method has been used successfully with the azodye 1,3-dihydroxy-2,4,6-tri(p-azophenyl-arsonic acid) benzene and with pneumococcus polysaccharide Type III. The antipneumococcus sera were found to precipitate the polysaccharide of Type III but not those of Types I and VIII and to agglutinate pneumococci of Type III but not those of Types I and II

Strongly correlated fermions on a kagome lattice

We study a model of strongly correlated spinless fermions on a kagome lattice at 1/3 filling, with interactions described by an extended Hubbard Hamiltonian. An effective Hamiltonian in the desired strong correlation regime is derived, from which the spectral functions are calculated by means of exact diagonalization techniques. We present our numerical results with a view to discussion of possible signatures of confinement/deconfinement of fractional charges.Comment: 10 pages, 10 figure

On the variability of return periods of European winter precipitation extremes over the last five centuries

International audienceWe investigate the changes of extreme European winter (December?February) precipitation over the last half millennium and show for various European regions that return periods of extremely wet and dry winters are subject to significant changes both before and after the onset of anthropogenic influences. Additionally, we examine the spatial pattern of the changes of the extremes covering the last 300 years where data quality is sufficient. Over central and eastern Europe dry winters occurred more frequently during the 18th and the second part of the 19th century relative to 1951?2000. Dry winters were less frequent during both the 18th and 19th century over the British Isles and the Mediterranean. Wet winters have been less abundant during the last three centuries compared to 1951?2000 except during the early 18th century in central Europe. Although winter precipitation extremes are affected by climate change, no obvious connection of these changes was found to solar, volcanic or anthropogenic forcing. However, physically meaningful interpretation with atmospheric circulation changes was possible

Structure and optical properties of high light output halide scintillators

Structural and optical properties of several high light output halide scintillators and closely related materials are presented based on first principles calculations. The optical properties are based on the Engel-Vosko generalized gradient approximation and the recently developed density functional of Tran and Blaha. The materials investigated are BaBr$_2$, BaIBr, BaCl$_2$, BaF$_2$, BaI$_2$, BiI$_3$, CaI$_2$, Cs$_2LiYCl$_6$, CsBa$_2$Br$_5$, CsBa$_2$I$_5$, K$_2$LaBr$_5$, K$_2$LaCl$_5$,K$_2$LaI$_5$, LaBr$_3$, LaCl$_3$, SrBr$_2$, and YI$_3$. For comparison results are presented for the oxide CdWO$_4$. We find that the Tran Blaha functional gives greatly improved band gaps and optical properties in this class of materials. Furthermore, we find that unlike CdWO$_4$, most of these halides are highly isotropic from an optical point of view even though in many cases the crystal structures and other properties are not. This general result is rationalized in terms of halide chemistry. Implications for the development of ceramic halide scintillators are discussed

Electronic and magnetic properties of the ionic Hubbard model on the striped triangular lattice at 3/4 filling

We report a detailed study of a model Hamiltonian which exhibits a rich interplay of geometrical spin frustration, strong electronic correlations, and charge ordering. The character of the insulating phase depends on the magnitude of Delta/|t| and on the sign of t. We find a Mott insulator for Delta >> U >> |t|; a charge transfer insulator for U >> \Delta >> |t|; and a correlated covalent insulator for U >> \Delta ~ |t|. The charge transfer insulating state is investigated using a strong coupling expansion. The frustration of the triangular lattice can lead to antiferromagnetism or ferromagnetism depending on the sign of the hopping matrix element, t. We identify the "ring" exchange process around a triangular plaquette which determines the sign of the magnetic interactions. Exact diagonalization calculations are performed on the model for a wide range of parameters and compared to the strong coupling expansion. The regime U >> \Delta ~ |t| and t<0 is relevant to Na05CoO2. The calculated optical conductivity and the spectral density are discussed in the light of recent experiments on Na05CoO2.Comment: 15 pages, 15 figure

Impurity induced spin-orbit coupling in graphene

We study the effect of impurities in inducing spin-orbit coupling in graphene. We show that the sp3 distortion induced by an impurity can lead to a large increase in the spin-orbit coupling with a value comparable to the one found in diamond and other zinc-blende semiconductors. The spin-flip scattering produced by the impurity leads to spin scattering lengths of the order found in recent experiments. Our results indicate that the spin-orbit coupling can be controlled via the impurity coverage.Comment: 4 pages, 6 figure

Vacancy complexes with oversized impurities in Si and Ge

In this paper we examine the electronic and geometrical structure of impurity-vacancy complexes in Si and Ge. Already Watkins suggested that in Si the pairing of Sn with the vacancy produces a complex with the Sn-atom at the bond center and the vacancy split into two half vacancies on the neighboring sites. Within the framework of density-functional theory we use two complementary ab initio methods, the pseudopotential plane wave (PPW) method and the all-electron Kohn-Korringa-Rostoker (KKR) method, to investigate the structure of vacancy complexes with 11 different sp-impurities. For the case of Sn in Si, we confirm the split configuration and obtain good agreement with EPR data of Watkins. In general we find that all impurities of the 5sp and 6sp series in Si and Ge prefer the split-vacancy configuration, with an energy gain of 0.5 to 1 eV compared to the substitutional complex. On the other hand, impurities of the 3sp and 4sp series form a (slightly distorted) substitutional complex. Al impurities show an exception from this rule, forming a split complex in Si and a strongly distorted substitutional complex in Ge. We find a strong correlation of these data with the size of the isolated impurities, being defined via the lattice relaxations of the nearest neighbors.Comment: 8 pages, 4 bw figure

On confined fractional charges: a simple model

We address the question whether features known from quantum chromodynamics (QCD) can possibly also show up in solid-state physics. It is shown that spinless fermions of charge $e$ on a checkerboard lattice with nearest-neighbor repulsion provide for a simple model of confined fractional charges. After defining a proper vacuum the system supports excitations with charges $\pm e/2$ attached to the ends of strings. There is a constant confining force acting between the fractional charges. It results from a reduction of vacuum fluctuations and a polarization of the vacuum in the vicinity of the connecting strings.Comment: 5 pages, 3 figure

Structural motifs of biomolecules

Biomolecular structures are assemblies of emergent anisotropic building modules such as uniaxial helices or biaxial strands. We provide an approach to understanding a marginally compact phase of matter that is occupied by proteins and DNA. This phase, which is in some respects analogous to the liquid crystal phase for chain molecules, stabilizes a range of shapes that can be obtained by sequence-independent interactions occurring intra- and intermolecularly between polymeric molecules. We present a singularityfree self-interaction for a tube in the continuum limit and show that this results in the tube being positioned in the marginally compact phase. Our work provides a unified framework for understanding the building blocks of biomolecules.Comment: 13 pages, 5 figure

Trion ground state, excited states and absorption spectrum using electron-exciton basis

We solve the Schr\"{o}dinger equation for two electrons plus one hole by writing it in the electron-exciton basis. The main advantage of this basis is to eliminate the exciton contribution from the trion energy in a natural way. The interacting electron-exciton system is treated using the recently developed composite boson many-body formalism which allows an exact handling of electron exchange. We numerically solve the resulting electron-exciton Schr\"{o}dinger equation, with the exciton levels restricted to the lowest $1s, 2s$ and $3s$ states, and we derive the trion ground state energy as a function of the electron-to-hole mass ratio. While our results are in reasonable agreement with those obtained through the best variational methods using free carrier basis, this electron-exciton basis is mostly suitable to easily reach the bound and unbound trion excited states. Through their wave functions, we here calculate the optical absorption spectrum in the presence of hot carriers for 2D quantum wells. We find large peaks located at the exciton levels, which are attributed to electron-exciton (unbound) scattering states, and small peaks identified with trion bound states.Comment: 16 pages; 15 figure