Dipolar effect in coherent spin mixing of two atoms in a single optical lattice site

We show that atomic dipolar effects are detectable in the system that recently demonstrated two-atom coherent spin dynamics within individual lattice sites of a Mott state. Based on a two-state approximation for the two-atom internal states and relying on a variational approach, we have estimated the spin dipolar effect. Despite the absolute weakness of the dipole-dipole interaction, it is shown that it leads to experimentally observable effects in the spin mixing dynamics.     

Antihydrogen formation by autoresonant excitation of antiproton plasmas

In efforts to trap antihydrogen, a key problem is the vast disparity between the neutral trap energy scale ( $\sim\!50\,\upmu\mathrm{eV}$ ), and the energy scales associated with plasma confinement and space charge (~1 eV). In order to merge charged particle species for direct recombination, the larger energy scale must be overcome in a manner that minimizes the initial antihydrogen kinetic energy. This issue motivated the development of a novel injection technique utilizing the inherent nonlinear nature of particle oscillations in our traps. We demonstrated controllable excitation of the center-of-mass longitudinal motion of a thermal antiproton plasma using a swept-frequency autoresonant drive. When the plasma is cold, dense and highly collective in nature, we observe that the entire system behaves as a single-particle nonlinear oscillator, as predicted by a recent theory. In contrast, only a fraction of the antiprotons in a warm or tenuous plasma can be similarly excited. Antihydrogen was produced and trapped by using this technique to drive antiprotons into a positron plasma, thereby initiating atomic recombination. The nature of this injection overcomes some of the difficulties associated with matching the energies of the charged species used to produce antihydrogen.     

Driven spatially autoresonant stimulated Raman scattering in the kinetic regime

The autoresonant behavior of Langmuir waves excited by stimulated Raman scattering (SRS) is clearly identified in particle-in-cell (PIC) simulations in an inhomogeneous plasma. As previously shown via a 3-wave coupling model [T. Chapman et al., Phys. Plasmas 17, 122317 (2010)], weakly kinetic effects such as trapping can be described via an amplitude-dependent frequency shift that compensates the dephasing of the resonance of SRS due to the inhomogeneity. The autoresonance (AR) leads to phase locking and to growth of the Langmuir wave beyond the spatial amplification expected from Rosenbluth's model in an inhomogeneous profile [M. N. Rosenbluth, Phys. Rev. Lett. 29, 565 (1972)]. Results from PIC simulations and from a 3-wave coupling code show very good agreement, leading to the conclusion that AR arises even beyond the so-called weakly kinetic regime.     

Role of nonlinear coupling and density fluctuations in magnetic-fluctuation-induced particle transport

Three-wave nonlinear coupling among spatial Fourier modes of density and magnetic fluctuations is directly measured in a magnetically confined toroidal plasma. Density fluctuations are observed to gain (lose) energy from (to) either equilibrium or fluctuating fields depending on the mode number. Experiments indicate that nonlinear interactions alter the phase relation between density and magnetic fluctuations, leading to strong particle transport.     

All-fiber integrated 10 GHz repetition rate femtosecond laser source based on Raman compression of pulses generated through spectral masking of a phase-modulated diode

We report the development of a 10?GHz repetition rate all-fiber integrated femtosecond source tunable around 1.55?μm. A phase modulator and sharp spectral filter are used to convert the output of a tunable CW diode to a 10?GHz pulse train. These pulses are compressed using Raman soliton adiabatic compression in a 21?km long length of fiber to generate sub-300-fs duration pulses at a 10?GHz repetition rate. By tuning the wavelength of the diode and appropriate filtering, similar performance was achieved over a 20?nm bandwidth.     

A Natural Transition Between Equilibrium Patterns of Dislocation Dipoles

The equilibrium configurations of a row of uniformly distributed dislocation dipoles are first studied. The analysis is then generalised to study dipoles in two-dimensional rectangular periodic lattices. By examining the stability of the equilibrium configurations we find that the system may undergo a natural transition from the Taylor lattice to a row of dipole walls. This bifurcation may be involved in the transition from channel-vein to persistent slip band (PSB) structures in the early stage of metal fatigue.     

General method for nucleophilic aromatic substitution of aryl fluorides and chlorides with dimethylamine using hydroxide-assisted decomposition of N,N-dimethylforamide

A practical and convenient procedure for the nucleophilic aromatic substitution of aryl fluorides and chlorides with dimethylamine was developed using a hydroxide-assisted thermal decomposition of N,N-dimethylforamide. These conditions are tolerant of nitro, nitrile, aldehyde, ketone, and amide groups but will undergo acyl substitution to form amides for methyl esters and acyl chlorides. Isolated yields of the products range from 44% to 98%, with the majority being greater than 70% for 17 examples.     

Design of a mouse restraint for synchrotron‐based computed tomography imaging

High‐resolution computed tomography (CT) imaging of a live animal within a lead‐lined synchrotron light hutch presents several unique challenges. In order to confirm that the animal is under a stable plane of anaesthesia, several physiological parameters (e.g. heart rate, arterial oxygen saturation, core body temperature and respiratory rate) must be remotely monitored from outside the imaging hutch. In addition, to properly scan the thoracic region using CT, the animal needs to be held in a vertical position perpendicular to the fixed angle of the X‐ray beam and free to rotate 180°–360°. A new X‐ray transparent mouse restraint designed and fabricated using computer‐aided design software and three‐dimensional rapid prototype printing has been successfully tested at the Biomedical Imaging and Therapy bending‐magnet (BMIT‐BM) beamline at the Canadian Light Source.