Rational design of all organic polymer dielectrics.

To date, trial and error strategies guided by intuition have dominated the identification of materials suitable for a specific application. We are entering a data-rich, modelling-driven era where such Edisonian approaches are gradually being replaced by rational strategies, which couple predictions from advanced computational screening with targeted experimental synthesis and validation. Here, consistent with this emerging paradigm, we propose a strategy of hierarchical modelling with successive downselection stages to accelerate the identification of polymer dielectrics that have the potential to surpass 'standard' materials for a given application. Successful synthesis and testing of some of the most promising identified polymers and the measured attractive dielectric properties (which are in quantitative agreement with predictions) strongly supports the proposed approach to material selection.

Rejection-free Monte Carlo scheme for anisotropic particles.

We extend the geometric cluster algorithm [J. Liu and E. Luijten, Phys. Rev. Lett. 92, 035504 (2004)], a highly efficient, rejection-free Monte Carlo scheme for fluids and colloidal suspensions, to the case of anisotropic particles. This is made possible by adopting hyperspherical boundary conditions. A detailed derivation of the algorithm is presented, along with extensive implementation details as well as benchmark results. We describe how the quaternion notation is particularly suitable for the four-dimensional geometric operations employed in the algorithm. We present results for asymmetric Lennard-Jones dimers and for the Yukawa one-component plasma in hyperspherical geometry. The efficiency gain that can be achieved compared to conventional, Metropolis-type Monte Carlo simulations is investigated for rod-sphere mixtures as a function of rod aspect ratio, rod-sphere diameter ratio, and rod concentration. The effect of curved geometry on physical properties is addressed.

Nanoparticle-controlled aggregation of colloidal tetrapods.

Tetrapods are among the most promising building blocks for nanoscale self-assembly, offering various desirable features. Whereas these particles can be fabricated with remarkable precision, comparatively less is known about their aggregation behavior. Employing a novel, powerful simulation method, we demonstrate that charged nanoparticles offer considerable control over the assembly of tip-functionalized tetrapods. Extending these findings to tetrapods confined to a gas/liquid interface, we show that regular structures can be achieved even without functionalization.

Improved rejection of transmitter noise: a convenient scheme with resonant crossed diodes.

A method is presented for improved rejection of transmitter noise in the duplexer (transmit-receive switch). The capacitance of a set of crossed diodes forms a resonant circuit with a length of coaxial cable. The rejection of our resonant design is 60 dB, compared with only 12-15 dB for the usual method, all measured at 175 MHz. Tuning the entire duplexer to different frequencies is convenient, requiring only two new lengths of cable. The scheme is most useful with ungated linear rf power amplifiers at very high frequencies (above 100 MHz), where transmitter noise can be a severe problem.

Frequency shifts in parametrically enhanced low-field MR detection.

A high-amplitude, high-frequency readout field has previously been proposed for use with low-field MR. Because the resulting modulation sidebands are at higher frequencies than the low-field steady precession, improved detection sensitivity results. However, if the ac readout field is inhomogeneous, it will necessarily have transverse components resulting in frequency shifts and broadening of the MR signal. Numerical solutions of Bloch's equations are compared to the Bloch-Siegert result to assess the size of the frequency shifts. A formula is derived by the average Hamiltonian method and provides an excellent fit to the numerically obtained shifts.