Smart Loads for Voltage Control in Distribution Networks

This paper shows that the smart loads (SLs) could be effective in mitigating voltage problems caused by photovoltaic (PV) generation and electric vehicle (EV) charging in low-voltage (LV) distribution networks. Limitations of the previously reported SL configuration with only series reactive compensator (SLQ) (one converter) is highlighted in this paper. To overcome these limitations, an additional shunt converter is used in back-to-back (B2B) configuration to support the active power exchanged by the series converter, which increases the flexibility of the SL without requiring any energy storage. Simulation results on a typical U.K. LV distribution network are presented to compare the effectiveness of an SL with B2B converters (SLBCs) against an SLQ in tackling under- and over-voltage problems caused by EV or PV. It is shown that SLBCs can regulate the main voltage more effectively than SLQs especially under overvoltage condition. Although two converters are required for each SLBC, it is shown that the apparent power capacity of each converter is required to be significantly less than that of an equivalent SLQ

A radiative transfer scheme for cosmological reionization based on a local Eddington tensor

A radiative transfer scheme is presented, based on a moment description of the equation of radiative transfer and the so-called ``M1 closure model'' for the Eddington tensor. This model features a strictly hyperbolic transport step for radiation: it has been implemented using standard Godunov--like techniques in a new code called ATON. Coupled to simple models of ionization chemistry and photo-heating, ATON is able to reproduce the results of other schemes on a various set of standard tests such as the expansion of a HII region, the shielding of the radiation by dense clumps and cosmological ionization by multiple sources. Being simple yet robust, such a scheme is intended to be naturally and easily included in grid--based cosmological fluid solvers.Comment: 14 pages, 13 figures, submitted to MNRA

Emergence of Topological and Strongly Correlated Ground States in trapped Rashba Spin-Orbit Coupled Bose Gases

We theoretically study an interacting few-body system of Rashba spin-orbit coupled two-component Bose gases confined in a harmonic trapping potential. We solve the interacting Hamiltonian at large Rashba coupling strengths using Exact Diagonalization scheme, and obtain the ground state phase diagram for a range of interatomic interactions and particle numbers. At small particle numbers, we observe that the bosons condense to an array of topological states with n+1/2 quantum angular momentum vortex configurations, where n = 0, 1, 2, 3... At large particle numbers, we observe two distinct regimes: at weaker interaction strengths, we obtain ground states with topological and symmetry properties that are consistent with mean-field theory computations; at stronger interaction strengths, we report the emergence of strongly correlated ground states.Comment: 14 pages, 9 figure

Reduced chemistry for butanol isomers at engine-relevant conditions

Butanol has received significant research attention as a second-generation biofuel in the past few years. In the present study, skeletal mechanisms for four butanol isomers were generated from two widely accepted, well-validated detailed chemical kinetic models for the butanol isomers. The detailed models were reduced using a two-stage approach consisting of the directed relation graph with error propagation and sensitivity analysis. During the reduction process, issues were encountered with pressure-dependent reactions formulated using the logarithmic pressure interpolation approach; these issues are discussed and recommendations made to avoid ambiguity in its future implementation in mechanism development. The performance of the skeletal mechanisms generated here was compared with that of detailed mechanisms in simulations of autoignition delay times, laminar flame speeds, and perfectly stirred reactor temperature response curves and extinction residence times, over a wide range of pressures, temperatures, and equivalence ratios. The detailed and skeletal mechanisms agreed well, demonstrating the adequacy of the resulting reduced chemistry for all the butanol isomers in predicting global combustion phenomena. In addition, the skeletal mechanisms closely predicted the time-histories of fuel mass fractions in homogeneous compression-ignition engine simulations. The performance of each butanol isomer was additionally compared with that of a gasoline surrogate with an antiknock index of 87 in a homogeneous compression-ignition engine simulation. The gasoline surrogate was consumed faster than any of the butanol isomers, with tert-butanol exhibiting the slowest fuel consumption rate. While n-butanol and isobutanol displayed the most similar consumption profiles relative to the gasoline surrogate, the two literature chemical kinetic models predicted different orderings.Comment: 39 pages, 16 figures. Supporting information available via https://doi.org/10.1021/acs.energyfuels.6b0185

The Unexpected Impact of Information-Sharing on US Pharmaceutical Supply-Chains

This paper examines the introduction of information-sharing into the supply chains for pharmaceutical products in the United States. This introduction was unusual for several reasons. First, it was catalyzed from outside the industry, by a Securities and Exchange Commission (SEC) investigation into improper financial reporting by a single manufacturer. Second, it was initiated by pharmaceutical manufacturers in order to keep distributor inventories low. Third, although its effect on pharmaceutical distributors has been profound, evidence indicates that information-sharing has had no impact on pharmaceutical manufacturers' own inventorymanagement practices.

Half-quantum vortex state in a spin-orbit coupled Bose-Einstein condensate

We investigate theoretically the condensate state and collective excitations of a two-component Bose gas in two-dimensional harmonic traps subject to isotropic Rashba spin-orbit coupling. In the weakly interacting regime when the inter-species interaction is larger than the intra-species interaction ($g_{\uparrow\downarrow}>g$), we find that the condensate ground state has a half-quantum-angular-momentum vortex configuration with spatial rotational symmetry and skyrmion-type spin texture. Upon increasing the interatomic interaction beyond a threshold $g_{c}$, the ground state starts to involve higher-order angular momentum components and thus breaks the rotational symmetry. In the case of $g_{\uparrow\downarrow}<g$, the condensate becomes unstable towards the superposition of two degenerate half-quantum vortex states. Both instabilities (at $g>g_{c}$ and $g_{\uparrow\downarrow}<g$) can be determined by solving the Bogoliubov equations for collective density oscillations of the half-quantum vortex state, and by analyzing the softening of mode frequencies. We present the phase diagram as functions of the interatomic interactions and the spin-orbit coupling. In addition, we directly simulate the time-dependent Gross-Pitaevskii equation to examine the dynamical properties of the system. Finally, we investigate the stability of the half-quantum vortex state against both the trap anisotropy and anisotropy in the spin-orbit coupling term.Comment: 13 pages, 18 figure

Interaction of Atomic and Molecular Hydrogen with Tholin Surfaces at Low Temperatures

We study the interaction of atomic and molecular hydrogen with a surface of tholin, a man-made polymer considered to be an analogue of aerosol particles present in Titan's atmosphere, using thermal programmed desorption at low temperatures below 30 K. The results are fitted and analyzed using a fine-grained rate equation model that describes the diffusion, reaction and desorption processes. We obtain the energy barriers for diffusion and desorption of atomic and molecular hydrogen. These barriers are found to be in the range of 30 to 60 meV, indicating that atom/molecule-surface interactions in this temperature range are dominated by weak adsorption forces. The implications of these results for the understanding of the atmospheric chemistry of Titan are discussed.Comment: 30 pages, 11 figure

Negative-Index Refraction in a Lamellar Composite with Alternating Single Negative Layers

Negative-index refraction is achieved in a lamellar composite with epsilon-negative (ENG) and mu-negative (MNG) materials stacked alternatively. Based on the effective medium approximation, simultaneously negative effective permittivity and permeability of such a lamellar composite are obtained theoretically and further proven by full-wave simulations. Consequently, the famous left-handed metamaterial comprising split ring resonators and wires is interpreted as an analogy of such an ENG-MNG lamellar composite. In addition, beyond the effective medium approximation, the propagating field squeezed near the ENG/MNG interface is demonstrated to be left-handed surface waves with backward phase velocity.Comment: 18 pages, 6 figure