Plant Immune Responses: Aphids Strike Back.

To survive and complete their life cycle, herbivorous insects face the difficult challenge of coping with the arsenal of plant defences. A new study reports that aphids secrete evolutionarily conserved cytokines in their saliva to suppress host immune responses

Large-N expansion based on the Hubbard operator path integral representation and its application to the t-J model II. The case for finite JJ

We have introduced a new perturbative approach for $t-J-V$ model where Hubbard operators are treated as fundamental objects. Using our vertices and propagators we have developed a controllable large-N expansion to calculate different correlation functions. We have investigated charge density-density response and the phase diagram of the model. The charge correlations functions are not very sensitive to the value of $J$ and they show collective peaks (or zero sound) which are more pronounced when they are well separated (in energy) from the particle-hole continuum. For a given $J$ a Fermi liquid state is found to be stable for doping $\delta$ larger than a critical doping $\delta_c$. $\delta_c$ decreases with decreasing $J$. For the physical region of the parameters and, for $\delta< \delta_c$, the system enters in an incommensurate flux or DDW phase. The inclusion of the nearest-neighbors Coulomb repulsion $V$ leads to a CDW phase when $V$ is larger than a critical value $V_c$. The dependence of $V_c$ with $\delta$ and $J$ is shown. We have compared the results with other ones in the literature.Comment: 10 pages, 8 figures, to appear in Phys. Rev.

Effect of dimensionality on the charge-density-wave in few-layers 2H-NbSe2_2

We investigate the charge density wave (CDW) instability in single and double layers, as well as in the bulk 2H-NbSe$_{2}$. We demonstrate that the density functional theory correctly describes the metallic CDW state in the bulk 2H-NbSe$_{2}$. We predict that both mono- and bilayer NbSe$_{2}$ undergo a CDW instability. However, while in the bulk the instability occurs at a momentum $\mathbf{q}_{CDW}\approx{2/3}\mathbf{\Gamma M}$, in free-standing layers it occurs at $\mathbf{q}_{CDW}\approx{1/2}\mathbf{\Gamma M}$. Furthermore, while in the bulk the CDW leads to a metallic state, in a monolayer the ground state becomes semimetallic, in agreement with recent experimental data. We elucidate the key role that an enhancement of the electron-phonon matrix element at $\mathbf{q}\approx\mathbf{q}_{CDW}$ plays in forming the CDW ground state.Comment: 4 pages 5 figure

Electron-phonon coupling and phonon self-energy in MgB2_2: do we really understand MgB2_2 Raman spectra ?

We consider a model Hamiltonian fitted on the ab-initio band structure to describe the electron-phonon coupling between the electronic $\sigma-$bands and the phonon E$_{2g}$ mode in MgB$_2$. The model allows for analytical calculations and numerical treatments using very large k-point grids. We calculate the phonon self-energy of the E$_{2g}$ mode along two high symmetry directions in the Brillouin zone. We demonstrate that the contribution of the $\sigma$ bands to the Raman linewidth of the E$_{2g}$ mode via the electron-phonon coupling is zero. As a consequence the large resonance seen in Raman experiments cannot be interpreted as originated from the $E_{2g}$ mode at $\Gamma$. We examine in details the effects of Fermi surface singularities in the phonon spectrum and linewidth and we determine the magnitude of finite temperature effects in the the phonon self-energy. From our findings we suggest several possible effects which might be responsible for the MgB$_2$ Raman spectra.Comment: 10 pages, 9 figure

Violation of Ioffe-Regel condition but saturation of resistivity of the high Tc cuprates

We demonstrate that the resistivity data of a number of high Tc cuprates, in particular La(2-x)SrxCuO4, are consistent with resistivity saturation, although the Ioffe-Regel condition is strongly violated. By using the f-sum rule together with calculations of the kinetic energy in the t-J model, we show that the saturation resistivity is unusually large. This is related to the strong reduction of the kinetic energy due to strong correlation effects. The fulfilment of the Ioffe-Regel condition for conventional transition metal compounds is found to be somewhat accidental.Comment: 4 pages, RevTeX, 2 eps figures, additional material available at http://www.mpi-stuttgart.mpg.de/andersen/saturation

Self-assembly in surfactant-based mixtures driven by acid–base reactions: bis(2-ethylhexyl) phosphoric acid– n-octylamine systems

Structural and dynamic features of bis(2-ethylhexyl) phosphoric acid (HDEHP)–n-octylamine (NOA) mixtures as a function of the NOA mole fraction (XNOA) have been investigated by SAXS, WAXS, IR, dielectric spectroscopy and polarized optical microscopy. In the 0 ¡ XNOA , 0.5 range, mixtures are transparent liquids, while the abrupt formation of a waxy solid characterized by an hexagonal bidimensional structure occurs at XNOA = 0.5. Such a composition-induced phase transition results from the synergetic effect of the progressive increase in number density of ordered HDEHP–NOA nanodomains with XNOA. Mainly driven by an HDEHP to NOA proton transfer, the increase of structural order with XNOA arises from the progressive substitution of loosely hydrogen bonded HDEHP–HDEHP aggregates with strongly bonded NOA–HDEHP ones. Analysis of SAXS patterns at temperatures in the 10–70 uC range emphasized that these local structures are scarcely impacted by an increase of thermal fluctuations. Effects due to the steric compatibility between HDEHP and NOA apolar moieties have been highlighted. Overall, the results allow us to emphasize the role of specific polar and apolar interactions joined to steric effects in regulating the molecular organization in surfactant mixtures and can be used to design novel materials with planned physico-chemical properties

Modeling of the particle scattering structure factor for branched bio-polymers in solution: A X-ray scattering study

We present a study which illustrates the modeling of the Particle Scattering Structure Factor from Small Angle X-ray Scattering (SAXS) data. The studied sample was a poly(amidoamine) Pamam dendrimers in water solution. The intra-particle form factor P(q) has been analyzed employing an inverse Fourier transformation which allows to obtain the particle pair distance distribution function and to gain information about dendrimer shape. The experimental inter-dendrimer structure factor S(q) has been analysed in the framework of liquid integral equation theory for charged systems in solution. From that, we derive an effective interparticle interaction composed of a screened Coulombic plus hard-sphere repulsion potential, which allow the estimation of the dendrimer effective surface charge Zeff. The present analysis, applied to a Pamam dendrimers in water solution, strongly supports the finding that structures and interaction of dendrimer is strongly influenced by charge effects. As a result, this quantity can be considered as a crucial parameters for the modulation of the degree of structural organization in solution, suitable for a number of potential applications

Clinical experience with Timentin in severe hospital infections

Sixty-four severe infections in hospitalized patients were treated with intravenous Timentin. Most patients (mean age: 50-5 years, range 18-85) had serious underlying conditions such as agranulocytosis, heart failure, cancer, diabetes mellitus, chronic alcoholism or other functional or anatomical abnormalities. Forty-three episodes were bacteriologically proved, and bacteraemia was diagnosed in 18. The sites of infection were: lower respiratory tract (10), upper respiratory tract (10), soft tissues(9), urinary tract (7), bones (6), peritoneal cavity (3), meninges (1) and pelvis (1). Inaddition, 13 episodes of fever and four of septicaemia in patients with agranulocytosis were treated with Timentin plus amilcacin. Overall, 59% of the episodes were cured, 14% improved and 17% failed to respond. In 9% of cases the efficacy of the Timentin was unassessable mainly because of concurrent administration of other antimicrobials. Failure appeared to be more frequent in soft tissue and intra-abdominal infections, in patients infected with bacteria susceptibleto Timentin but resistant to ticarcillin and in patients superinfected with Timentin-resistant strains. Major side effects were haemorrhagic diathesis with platelet dysfunction (1), severe water sodium overload (1), and possibly pancreatitis (1).Other side effects were mild: catheter-related phlebitis, and abnormal but clinically insignificant laboratory test results. Timentin appears to be an effective and safebroad-spectrum combination which compares favourably with third-generation cephalosporins in the treatment of severe hospital infections. More experience is needed to decide whether the some what lower response rate in patients infected with ticarcillin-resistant strains is significan

Thermodynamic stabilities of ternary metal borides: An ab initio guide for synthesizing layered superconductors

Density functional theory calculations have been used to identify stable layered Li-$M$-B crystal structure phases derived from a recently proposed binary metal-sandwich (MS) lithium monoboride superconductor. We show that the MS lithium monoboride gains in stability when alloyed with electron-rich metal diborides; the resulting ordered Li$_{2(1-x)}M_x$B$_2$ ternary phases may form under normal synthesis conditions in a wide concentration range of $x$ for a number of group-III-V metals $M$. In an effort to pre-select compounds with the strongest electron-phonon coupling we examine the softening of the in-plane boron phonon mode at $\Gamma$ in a large class of metal borides. Our results reveal interesting general trends for the frequency of the in-plane boron phonon modes as a function of the boron-boron bond length and the valence of the metal. One of the candidates with a promise to be an MgB$_2$-type superconductor, Li$_2$AlB$_4$, has been examined in more detail: according to our {\it ab initio} calculations of the phonon dispersion and the electron-phonon coupling $\lambda$, the compound should have a critical temperature of $\sim4$ K.Comment: 10 pages, 9 figures, submitted to PR