A Novel Chiral Phase of Achiral Hard Triangles and an Entropy-Driven Demixing of Enantiomers

We investigate the phase behavior of a system of hard equilateral and right-angled triangles in two dimensions using Monte Carlo simulations. Hard equilateral triangles undergo a continuous isotropic-triatic liquid crystal phase transition at packing fraction $\phi=0.7$. Similarly, hard right-angled isosceles triangles exhibit a first-order phase transition from an isotropic fluid phase to a rhombic liquid crystal phase with a coexistence region $\phi \in \left[0.733,0.782\right]$. Both these liquid crystal phases undergo a continuous phase transition to their respective close-packed crystal structures at high pressures. Although the particles and their close-packed crystals are both achiral, the solid phases of equilateral and right-angled triangles exhibit spontaneous chiral symmetry breaking at sufficiently high packing fractions. The colloidal triangles rotate either in clockwise or anti-clockwise direction with respect to one of the lattice vectors for packing fractions higher than $\phi_\chi$. As a consequence, these triangles spontaneously form a regular lattice of left- or right-handed chiral holes which are surrounded by six triangles in the case of equilateral triangles and four or eight triangles for right-angled triangles. Moreover, our simulations show a spontaneous entropy-driven demixing transition of the right- and left-handed "enantiomers".Comment: 9 pages, 10 figure

Ultrasonic distance detection for a closed-loop spinal cord stimulation system

When stimulating the spinal cord at a constant strength, the current density in the spinal cord and thus the effects on chronic, intractable pain and vascular insufficiency will change with body position, due to the varying separation of the spinal cord and the stimulating electrode. The current density in the spinal cord has to remain between the perception and discomfort threshold (stimulation window) for a good therapeutic effect, i.e. that the patient does not suffer from pain. The stimulation window is very small. In current SCS systems the stimulus applied to the electrode is set at a constant value. A major improvement could be achieved when the distance between stimulation electrode and spinal cord could be measured and used to control the stimulus amplitude in a closed-loop system. An ultrasonic piezoelectric transducer was chosen to measure the distance between the electrode and the spinal cor

On the relation between adjacent inviscid cell type solutions to the rotating-disk equations

Over a large range of the axial coordinate a typical higher-branch solution of the rotating-disk equations consists of a chain of inviscid cells separated from each other by viscous interlayers. In this paper the leading-order relation between two adjacent cells will be established by matched asymptotic expansions for general values of the parameter appearing in the equations. It is found that the relation between the solutions in the two cells crucially depends on the behaviour of the tangential velocity in the viscous interlayer. The results of the theory are compared with accurate numerical solutions and good agreement is obtained

Non-Markovian entanglement dynamics in the presence of system-bath coherence

A complete treatment of the entanglement of two-level systems, which evolves through the contact with a thermal bath, must include the fact that the system and the bath are not fully separable. Therefore, quantum coherent superpositions of system and bath states, which are almost never fully included in theoretical models, are invariably present when an entangled state is prepared experimentally. We show their importance for the time evolution of the entanglement of two qubits coupled to independent baths. In addition, our treatment is able to handle slow and low-temperature thermal baths.Comment: Accepted for publication in Phys. Rev. Lett

The Correlation Between Star Formation and 21cm Emission During the Reionization Epoch

Reionization is thought to be dominated by low mass galaxies, while direct observations of resolved galaxies probe only the most massive, rarest objects. The cross-correlation between fluctuations in the surface brightness of the cumulative Ly-alpha emission (which serves as a proxy for the star formation rate) and the redshifted 21cm signal from neutral hydrogen in the intergalactic medium (IGM), will directly probe the causal link between the production of ionizing photons in galaxies and the reionization of the IGM. We discuss the prospects for detecting this cross-correlation for unresolved galaxies. We find that on angular scales <10 arc-minutes, detection will be practical using widefield near-IR imaging from space in combination with the forthcoming Mileura Widefield Array - Low Frequency Demonstrator. When redshifted 21cm observations of the neutral IGM are combined with space-based near-IR imaging of Ly-alpha emission, the detection on angular scales <3 arc-minutes will be limited by the sensitivity of the 21cm signal, even when a small aperture optical telescope (~2m) and a moderate field of view (~10 square degrees) are used. On scales >3 arc-minutes, the measurement of cross-correlation will be limited by the accuracy of the foreground sky subtraction.Comment: 12 pages. 5 figures. Submitted to MNRA

An optimised algorithm for ionized impurity scattering in Monte Carlo simulations

We present a new optimised model of Brookes-Herring ionized impurity scattering for use in Monte Carlo simulations of semiconductors. When implemented, it greatly decreases the execution time needed for simulations (typically by a factor of the order of 100), and also properly incorporates the great proportion of small angle scatterings that are neglected in the standard algorithm. It achieves this performance by using an anisotropic choice of scattering angle which accurately mimics the true angular distribution of ionized impurity scattering.Comment: 5 page