Novel cyclic amide heterodimer lansamide-2 from Clausena lansium

A new cyclic amide heterodimer has been isolated from Clausena-lansium leaves. The structure of this amide heterodimer was determined by X-ray crystallographic studies and spectrochemical evidence.     

Sub- and superluminal propagation of intense pulses in media with saturated and reverse absorption

We develop models for the propagation of intense pulses in solid state media which can have either saturated absorption or reverse absorption. We model subluminal propagation in ruby and superluminal propagation in alexandrite as three and four level systems, respectively, coupled to Maxwell's equations. We present results well beyond the traditional pump-probe approach and explain the experiments of Bigelow et al. [Phys. Rev. Lett. 90, 113903 (2003)]Science 301, 200 (2003)]] on solid state materials.     

Coupled folding-binding versus docking: a lattice model study

Using a simple hydrophobic/polar protein model, we perform a Monte Carlo study of the thermodynamics and kinetics of binding to a target structure for two closely related sequences, one of which has a unique folded state while the other is unstructured. We obtain significant differences in their binding behavior. The stable sequence has rigid docking as its preferred binding mode, while the unstructured chain tends to first attach to the target and then fold. The free-energy profiles associated with these two binding modes are compared.     

Three solutions of constant sign for a system of discrete equations

We consider the following system of discrete equations

Inducing disallowed two-atom transitions with temporally entangled photons

Two uncoupled two-level atoms cannot be jointly excited by classical light under general circumstances, due to destructive interference of excitation pathways in two-photon absorption. However, with temporally entangled light, two-atom excitation is shown possible. Photons arising from three-level cascade decay are intrinsically ordered in time of emission. This field correlation induces a joint resonance in the two-atom excitation probability via suppression of one of the time-ordered excitation pathways. The relative gain in two-photon absorption increases with the time-frequency entanglement.     

Atomic absorbers for controlling pulse propagation in resonators

We consider pulse propagation through a Fabry-Perot cavity with silver mirrors that contain macroscopic samples of resonant absorbers. We show that the pulse velocity can be tuned from subluminal to superluminal in a strongly coupled atom-cavity system. We delineate the effects of the interplay of cavity and absorbers. We demonstrate the saturation effects of pulse advancement with increasing mirror thickness and atomic damping.     

Molecular simulation of the reversible mechanical unfolding of proteins

In this work we have combined a Wang-Landau sampling scheme [F. Wang and D. Landau, Phys. Rev. Lett. 86, 2050 (2001)] with an expanded ensemble formalism to yield a simple and powerful method for computing potentials of mean force. The new method is implemented to investigate the mechanical deformation of proteins. Comparisons are made with analytical results for simple model systems such as harmonic springs and Rouse chains. The method is then illustrated on a model 15-residue alanine molecule in an implicit solvent. Results for mechanical unfolding of this oligopeptide are compared to those of steered molecular dynamics calculations.     

On nonoscillatory solutions of differential inclusions

This paper introduces a nonoscillatory theory for differential inclusions based on fixed point theory for multivalued maps.

     

Inhibition of decoherence due to decay in a continuum

We propose a scheme for slowing down decay into a continuum. We make use of a sequence of ultrashort 2pi pulses applied on an auxiliary transition of the system so that there is a destructive interference between the two transition amplitudes--one before the application of the pulse and the other after the application of the pulse. We give explicit results for a structured continuum. Our scheme can also inhibit unwanted transitions.     

Twin solutions to singular boundary value problems

In this paper we establish the existence of two nonnegative solutions to singular and singular focal boundary value problems. Our nonlinearity may be singular at , and/or .