210,332 research outputs found
Ballistic magneto-thermal transport in a Heisenberg spin chain at low temperatures
We study ballistic thermal transport in Heisenberg spin chain with
nearest-neighbor ferromagnetic interactions at low temperatures. Explicit
expressions for transmission coefficients are derived for thermal transport in
a periodic spin chain of arbitrary junction length by a spin-wave model. Our
analytical results agree very well with the ones from nonequilibrium Green's
function method. Our study shows that the transmission coefficient oscillates
with the frequency of thermal wave. Moreover, the thermal transmission shows
strong dependence on the intrachain coupling, the length of the spin chain, and
the external magnetic field. The results demonstrate the possibility of
manipulating spin-wave propagation and magnetothermal conductance in the
spin-chain junction by adjusting the intrachain coupling and/or the external
magnetic field.Comment: 6 pages, 7 figure
Shuttling heat across 1D homogenous nonlinear lattices with a Brownian heat motor
We investigate directed thermal heat flux across 1D homogenous nonlinear
lattices when no net thermal bias is present on average. A nonlinear lattice of
Fermi-Pasta-Ulam-type or Lennard-Jones-type system is connected at both ends to
thermal baths which are held at the same temperature on temporal average. We
study two different modulations of the heat bath temperatures, namely: (i) a
symmetric, harmonic ac-driving of temperature of one heat bath only and (ii) a
harmonic mixing drive of temperature acting on both heat baths. While for case
(i) an adiabatic result for the net heat transport can be derived in terms of
the temperature dependent heat conductivity of the nonlinear lattice a similar
such transport approach fails for the harmonic mixing case (ii). Then, for case
(ii), not even the sign of the resulting Brownian motion induced heat flux can
be predicted a priori. A non-vanishing heat flux (including a non-adiabatic
reversal of flux) is detected which is the result of an induced dynamical
symmetry breaking mechanism in conjunction with the nonlinearity of the lattice
dynamics. Computer simulations demonstrate that the heat flux is robust against
an increase of lattice sizes. The observed ratchet effect for such directed
heat currents is quite sizable for our studied class of homogenous nonlinear
lattice structures, thereby making this setup accessible for experimental
implementation and verification.Comment: 9 pages, 10 figures. Phys. Rev. E (in press
Antireflection silicon structures with hydrophobic property fabricated by three-beam laser interference
This paper demonstrates antireflective structures on silicon wafer surfaces with hydrophobic property fabricated by three-beam laser interference. In this work, a three-beam laser interference system was set up to generate periodic micro-nano hole structures with hexagonal distributions. Compared with the existing technologies, the array of hexagonally-distributed hole structures fabricated by three-beam laser interference reveals a design guideline to achieve considerably low solar-weighted reflectance (SWR) in the wavelength range of 300-780 nm. The resulting periodic hexagonally-distributed hole structures have shown extremely low SWR (1.86%) and relatively large contact angle (140°) providing with a self-cleaning capability on the solar cell surface
Space Alignment Based on Regularized Inversion Precoding in Cognitive Transmission
For a two-tier Multiple-Input Multiple-Output (MIMO) cognitive network with common receiver, the precoding matrix has a compact relationship with the capacity performance in the unlicensed secondary system. To increase the capacity of secondary system, an improved precoder based on the idea of regularized inversion for secondary transmitter is proposed. An iterative space alignment algorithm is also presented to ensure the Quality of Service (QoS) for primary system. The simulations reveal that, on the premise of achieving QoS for primary system, our proposed algorithm can get larger capacity in secondary system at low Signal-to-Noise Ratio (SNR), which proves the effectiveness of the algorithm
Robust optimization for energy transactions in multi-microgrids under uncertainty
Independent operation of single microgrids (MGs) faces problems such as low self-consumption of local renewable energy, high operation cost and frequent power exchange with the grid. Interconnecting multiple MGs as a multi-microgrid (MMG) is an effective way to improve operational and economic performance. However, ensuring the optimal collaborative operation of a MMG is a challenging problem, especially under disturbances of intermittent renewable energy. In this paper, the economic and collaborative operation of MMGs is formulated as a unit commitment problem to describe the discrete characteristics of energy transaction combinations among MGs. A two-stage adaptive robust optimization based collaborative operation approach for a residential MMG is constructed to derive the scheduling scheme which minimizes the MMG operating cost under the worst realization of uncertain PV output. Transformed by its KKT optimality conditions, the reformulated model is efficiently solved by a column-and-constraint generation (C&CG) method. Case studies verify the effectiveness of the proposed model and evaluate the benefits of energy transactions in MMGs. The results show that the developed MMG operation approach is able to minimize the daily MMG operating cost while mitigating the disturbances of uncertainty in renewable energy sources. Compared to the non-interactive model, the proposed model can not only reduce the MMG operating cost but also mitigate the frequent energy interaction between the MMG and the grid
Evaluation of the EMC environment generated by a static var compensator
Describes an evaluation of the EMC environment generated by a static var compensator
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