Coupling-induced oscillations in nonhomogeneous, overdamped, bistable systems

Coupling-induced oscillations in a homogeneous network of overdamped bistable systems have been previously studied both theoretically and experimentally for a system of N (odd) elements, unidirectionally coupled in a ring topology. In this work, we extend the analysis of this system to include a network of nonhomogeneous elements with respect to the parameter that controls the topology of the potential function and the bistability of each element. In particular, we quantify the effects of the nonhomogeneity on the onset of oscillations and the response of the network to external (assumed to be constant and very small) perturbations, using our (recently developed) coupled core fluxgate magnetometer as a representative system. The potential applications of this work include signal detection and characterization for a large class of sensor systems.     

Effective action in a general chiral model: Next to leading order derivative expansion in the worldline method

We present a formalism to determine the imaginary part of a general chiral model in the derivative expansion. Our formalism is based on the worldline path integral for the covariant current that can be given in an explicit chiral and gauge covariant form. The effective action is then obtained by integrating the covariant current, taking account of the anomaly.     

Slow light with cavity electromagnetically induced transparency

We report an experimental observation of slow light propagation in cold Rb atoms exhibiting cavity electromagnetically induced transparency (EIT). The steep slope of the atomic dispersion manifested by EIT reduces the light group velocity. The cavity filtering and feedback further contribute to the slowdown and delay of the light pulse propagation. A combination of the cavity and the EIT atomic system significantly improves the performance of the slow light propagation. A propagation time delay of approximately 200 ns was observed in the cavity and Rb EIT system, which is approximately 70 times greater than the time delay calculated for the light pulse propagation through the same Rb EIT system without the cavity.     

Solvent-induced acceleration of the rate of activation of a molecular reaction

An increase in the rates of activated processes with the coupling to the solvent has long been predicted through the phenomenological Langevin equation in the weak coupling regime. However, its direct observation in particle-based models has been elusive because the coupling typically places the processes in the spacial-diffusion limited regime wherein rates decrease with increasing friction. In this work, the forward and backward reaction rates of the LiNC<==>LiCN isomerization reaction in a bath of argon atoms at various densities have been calculated directly using molecular dynamics trajectories. The so-called Kramers turnover in the rate with microscopic friction is clearly visible, thus providing direct and unambiguous evidence for the energy-diffusion regime in which rates increase with friction.     

Semileptonic bc to cc and bb to bc baryon decays and heavy quark spin symmetry

We study the semileptonic decays of the lowest-lying bc baryons to the lowest-lying cc baryons （Ξ （＊） bc → Ξ （＊） cc and Ω （ ＊） bc → Ω （＊） cc ）,in the limit m b,m c Λ QCD and close to the zero recoil point.The separate heavy quark spin symmetries make it possible to describe all these decays using a single form factor.We also show how these constraints can be used to test the validity of different quark model calculations.bb to bc baryon decays are also discussed.     

Polyphosphinoborane Block Copolymer Synthesis Using Catalytic Reversible Chain-Transfer Dehydropolymerization

An amphiphilic block copolymer of polyphosphinoborane has been prepared by a mechanism-led strategy of the sequential catalytic dehydropolymerization of precursor monomers, H₃B ⋅ PRH₂ (R=Ph, n-hexyl), using the simple pre-catalyst [Rh(Ph₂PCH₂CH₂PPh₂)₂]Cl. Speciation, mechanism and polymer chain growth studies support a step-growth process where reversible chain transfer occurs, i.e. H₃B ⋅ PRH₂/oligomer/polymer can all coordinate with, and be activated by, the catalyst. Block copolymer [H₂BPPhH]₁₁₀-b-[H₂BP(n-hexyl)H]₁₁ can be synthesized and self-assembles in solution to form either rod-like micelles or vesicles depending on solvent polarity.     

Mechanochemical Desymmetrization of Unbiased Bis- and Tris-alkynes to Access 3,5-Isoxazoles-Alkyne Adducts and Unsymmetrical Bis-3,5-isoxazoles**

A mechanochemical desymmetrization of symmetrical bis- and tris-alkynes by a controlled 1,3-dipolar cycloaddition reaction using nitrile oxide dipoles (NOs). This operationally simple protocol allows access to 3,5-isoxazole-alkyne adducts from easily prepared or commercially available symmetrical bis- and tris-alkynes in moderate to excellent yields. In addition, we have highlighted the synthetic utility of 3,5-isoxazole-alkyne by developing a route to access, for the first time, β-ketoenamine-alkyne derivatives, and unsymmetrical bis-3,5-isoxazoles.