Dipolar interactions and origin of spin ice in ising pyrochlore magnets

Recent experiments suggest that the Ising pyrochlore magnets Ho2Ti2O7 and Dy2Ti2O7 display qualitative properties of the nearest-neighbor "spin ice" model. We discuss the dipolar energy scale present in both these materials and discuss how spin-ice behavior can occur despite the presence of long-range dipolar interactions. We present results of numerical simulations and a mean field analysis of Ising pyrochlore systems. Based on our quantitative theory, we suggest that the spin-ice behavior in these systems is due to long-range dipolar interactions, and that the nearest-neighbor exchange in Dy2Ti2O7 is antiferromagnetic.     

Photoassociative production and trapping of ultracold KRb molecules

We have produced ultracold heteronuclear KRb molecules by the process of photoassociation in a two-species magneto-optical trap. Following decay of the photoassociated KRb*, the molecules are detected using two-photon ionization and time-of-flight mass spectroscopy of KRb+. A portion of the metastable triplet molecules thus formed are magnetically trapped. Photoassociative spectra down to 91 cm(-1) below the K(4s)+Rb(5p(1/2)) asymptote have been obtained. We have made assignments to all eight of the attractive Hund's case (c) KRb* potential curves in this spectral region.     

Exact scalar field cosmologies in a higher derivative theory

We obtain exact cosmological solutions of a higher derivative theory described by the Lagrangian L=R+2αR ² in the presence of interacting scalar field. The interacting scalar field potential required for a known evolution of the FRW universe in the framework of the theory is obtained using a technique different from the usual approach to solve the Einstein field equations. We follow here a technique to determine potential similar to that used by Ellis and Madsen in Einstein gravity. Some new and interesting potentials are noted in the presence of R ² term in the Einstein action for the known behaviours of the universe. These potentials in general do not obey the slow rollover approximation.     

Energy transfer in Li(4p) + (Ar,H2,CH4) collisions

The direct collisional energy transfer processes of the excited states of Li(4p) by several gases are investigated under gas cell conditions. The nonreactive absorption profiles of the collision complex are monitored as a function of laser detuning from the Li(2s-4p) resonances. Pronounced structures in the absorption spectra along with high level ab initio calculations of the relevant potential energy surfaces are used to understand the experimental results.     

Orbital Angular Momentum in Scalar Diquark Model and QED

We compare the orbital angular momentum of the ‘quark’ in the scalar diquark model as well as that of the electron in QED (to order α) obtained from the Jaffe–Manohar decomposition to that obtained from the Ji relation. We estimate the importance of the vector potential in the definition of orbital angular momentum.     

An efficient one-pot synthesis of coumarin-amino acid derivatives as potential anti-inflammatory and antioxidant agents

Abstract

A series of seven coumarinyl-amino acid ester conjugates have been synthesized and characterized by NMR (¹H and 13C) and mass spectra. Further, the compounds were investigated for their therapeutic applications such as anti-inflammatory and antioxidant activities. Among the synthesized compounds most of the analogs showed good efficiency compared with the standard.     

The photoassociative spectroscopy, photoassociative molecule formation, and trapping of ultracold \mathsf{^{39}K^{85}Rb}

We have observed the photoassociative spectra of colliding ultracold ³⁹K and ⁸⁵Rb atoms to produce KRb* in all eight bound electronic states correlating with the ³⁹K (4s) + ⁸⁵Rb(5p _1/2 and 5p _3/2) asymptotes. These electronically excited KRb* ultracold molecules are detected after their radiative decay to the metastable triplet (a state and (in some cases) the singlet (X ground state. The triplet (a ultracold molecules are detected by two-photon ionization at 602.5 nm to form KRb ⁺ , followed by time-of-flight mass spectroscopy. We are able to assign a majority of the spectrum to three states (2(0 ⁺ ), 2(0^-), 2(1)) in a lower triad of states with similar C ₆ values correlating to the K(4s) + Rb (5p _1/2) asymptote; and to five states in an upper triad of three states (3(0 ⁺ ), 3(0^-), 3(1)) and a dyad of two states (4(1), 1(2)), with one set of similar C ₆ values within the upper triad and a different set of similar C ₆ values within the dyad. We are also able to make connection with the short-range spectra of Kasahara et al. [J. Chem. Phys. 111, 8857 (1999)], identifying three of our levels as v = 61, 62 and 63 of the 1 4(1) state they observed. We also argue that ultracold photoassociation to levels between the K(4s) + Rb (5p _3/2) and K(4s) + Rb (5p _1/2) asymptotes may be weakly or strongly predissociated and therefore difficult to observe by ionization of a (or X molecules; we do know from Kasahara et al. that levels of the 1 4(1) and 2 5(1) states in the intra-asymptote region are predissociated. A small fraction ( 1/3) of the triplet (a ultracold molecules formed are trapped in the weak magnetic field of our magneto-optical trap (MOT).Received: 22 September 2004, Published online: 23 November 2004PACS: 33.20.Fb Raman and Rayleigh spectra (including optical scattering) - 34.20.Cf Interatomic potentials and forces - 33.80.Ps Optical cooling of molecules; trapping