Continuous-wave frequency tripling and quadrupling by simultaneous three-wave mixings in periodically poled crystals: application to a two-step 1.19-10.71-microm frequency bridge

We observed cw third-harmonic generation in a periodically poled LiNbO(3) crystal by cascading optimally phase-matched second-harmonic and sum-frequency generation. Other processes, such as fourth-harmonic generation, are allowed by the flexibility of quasi-phase matching. We demonstrate a divide-by-nine (1.19- 10.71-microm) frequency chain that uses only two lasers.     

Exponentially small adiabatic invariant for the Schrödinger equation

We study an adiabatic invariant for the time-dependent Schrödinger equation which gives the transition probability across a gap from timet to timet. When the hamiltonian depends analytically on time, andt=–,t=+ we give sufficient conditions so that this adiabatic invariant tends to zero exponentially fast in the adiabatic limit.Supported by Fonds National Suisse de la Recherche, Grant 2000-5.600     

Correlation inequalities and uniqueness of the equilibrium state for the plane rotator ferromagnetic model

We derive new inequalities for the plane rotator ferromagnetic model and use them to obtain the following results:

1. If the model is isotropic, the derivability of the free energy as function of the magnetic fieldh implies the existence of a unique translation invariant Gibbs state and if furthermoreh=0 all Gibbs states are invariant by rotation of the spins.
2. If the model is anisotropic the above assertion holds forh non-zero.
3. If the model is anisotropic then there are at most two extremal translation invariant Gibbs states for almost all values of the anisotropy parameter.

     

Excited donor and acceptor states in zinc telluride

Excited shallow donor and acceptor states are observed in excitation spectra of donoracceptor pair luminescence in ZnTe. The experiments yield a donor ionization energyE _D =18.3±0.3 meV, and from the Li acceptor 2P _3/2, 2P _5/2( ₈), and 2P _5/2( ₇) states valence band parametersµ=0.60±0.10 and=0.22±0.05. The latter exceeds values derived from other experiments and indicates considerable nonspherical perturbations associated with this acceptor requiring an extension of existing theories for shallow acceptor states.     

Total Synthesis and Biological Evaluation of Heliolactone

Strigolactones are phytohormones, which affect diverse aspects of plant growth and development with potential application in modern agriculture. Recently, heliolactone has been isolated as a non‐canonical type of strigolactone from the root exudates of sunflower, and it could be involved in signaling in the rhizosphere as well as in planta. However, its biological activity is yet to be evaluated, due to its relative chemical instability and its low natural abundance. Herein, we describe the gram‐scale synthesis of heliolactone and its derivatives by using Stille cross‐coupling as the key bond‐forming reaction, and we disclose some of their biological activities (soil stability, binding ability to strigolactone receptor, corn germination, sunflower germination, Orobanche cumana germination and leaf senescence) in comparison with other canonical and non‐canonical strigolactones.     

Unexpected formation and structural characterisation of a novel rhodium B12 analogue

The metalation reactions of the 2,2'-bidipyrrin 4 with different rhodium(I) precursors yield the complexes 5 and 6 and the unusual corrinoid 7, depending only on the type of the ancillary ligand employed.     

Rigorous analysis of singularities and absence of analytic continuation at first-order phase-transition points in lattice-spin models

We report about two new rigorous results on the nonanalytic properties of thermodynamic potentials at first-order phase transition. For lattice models (d>or=2) with arbitrary finite state space, finite-range interactions which have two ground states, we prove that the pressure has no analytic continuation at the first-order phase-transition point, under the only further assumptions that the Peierls condition is satisfied for the ground states and that the temperature is sufficiently low. For Ising models with Kac potentials J(gamma)(x)=gamma(d)phi(gammax), where 00) and analyticity in the mean field limit (gamma SE pointing arrow 0).