Thermal effects on lattice strain in hcp Fe under pressure

We compute the c/a lattice strain versus temperature for nonmagnetic hcp iron at high pressures using both first-principles linear response quasiharmonic calculations based on the full potential linear-muffin-tin-orbital (LMTO) method and the particle-in-cell (PIC) model for the vibrational partition function using a tight-binding total-energy method. The tight-binding model shows excellent agreement with the all-electron LMTO method. When hcp structure is stable, the calculated geometric mean frequency and Helmholtz free energy of hcp Fe from PIC and linear response lattice dynamics agree very well, as does the axial ratio as a function of temperature and pressure. On-site anharmonicity proves to be small up to the melting temperature, and PIC gives a good estimate of its sign and magnitude. At low pressures, hcp Fe becomes dynamically unstable at large c/a ratios, and the PIC model might fail where the structure approaches lattice instability. The PIC approximation describes well the vibrational behavior away from the instability, and thus is a reasonable approach to compute high temperature properties of materials. Our results show significant differences from earlier PIC studies, which gave much larger axial ratio increases with increasing temperature, or reported large differences between PIC and lattice dynamics results.Comment: 9 figure

Dispersion Characteristics Analysis of One Dimensional Multiple Periodic Structures and Their Applications to Antennas

published_or_final_versio

One dimensional multiple periodic composite right/left handed (CRLH) structures

The wave-propagation characteristics in a one-dimensional multiple-periodic (MP) Composite right/left-handed (CRLH) structures is presented, where it is found that an increase in the number of unit cells in each supercell leads to new passbands and stopbands. To understand this phenomenon, the network parameters are employed for the theoretical analysis. Detailed dispersion characteristics and the relation between passbands and sub-periodicities are investigated using both analytical and full-wave results, and the reasons for their emergence is qualitatively discussed. Besides, its application to multi-band leaky-wave radiators is also suggested.published_or_final_versio

The multiple periodic structure antenna design

In this paper, the generalized analysis and novel application of the multiple periodic (MP) structure are proposed. Both transmission and radiation performances of one dimensional MP structures are studied. The dispersion relations are analyzed from both layered media (distributive) and lumped circuits aspects. Regarding each aspect, both non-dispersive (conventional) and dispersive (composite right/left-handed (CRLH)) materials are discussed. It is found that with the increase of the periodicity, multiple stopbands are open up due to the reflections. Meanwhile the space harmonic modes' separation distance is reduced in the dispersion diagrams. It leads to simultaneously dualistic (right- and left-handed) radiation performance and multi-beam property, and more abundant radiation modes are excited at relatively lower frequencies comparing with conventional periodic structures. A general dispersion relation formula and a general Bragg condition for MP structures are derived. The dispersion relation is simply described by the former, and the latter helps to indicate the stopbands locations and engineer the dispersion relation consequently. Applications of MP structures to phase reversal (PR) antennas are also presented in this paper. They experimentally veri¯es both transmission and radiation characteristics of MP structures. In each analysis, single (SP), double (DP) and triple periodic (TP) structures are presented and compared. This work would also contribute to designs of multi-band devices.postprin

Ferromagnetism in 2p Light Element-Doped II-oxide and III-nitride Semiconductors

II-oxide and III-nitride semiconductors doped by nonmagnetic 2p light elements are investigated as potential dilute magnetic semiconductors (DMS). Based on our first-principle calculations, nitrogen doped ZnO, carbon doped ZnO, and carbon doped AlN are predicted to be ferromagnetic. The ferromagnetism of such DMS materials can be attributed to a p-d exchange-like p-p coupling interaction which is derived from the similar symmetry and wave function between the impurity (p-like t_2) and valence (p) states. We also propose a co-doping mechanism, using beryllium and nitrogen as dopants in ZnO, to enhance the ferromagnetic coupling and to increase the solubility and activity

Finite-element-based generalized impedance boundary condition for modeling plasmonic nanostructures

The superior ability of plasmonic structures to manipulate light has propelled their extensive applications in nanophotonics techniques and devices. Computational electromagnetics plays a critical role in characterizing and optimizing the nanometallic structures. In this paper, a general numerical algorithm, which is different from the commonly used discrete dipole approximation, the finite-difference time-domain, and the surface integral equation (SIE) method, is proposed to model plasmonic nanostructures. In this algorithm, the generalized impedance boundary condition (GIBC) based on the finite element method (FEM) is formulated and converted to the SIE. The plasmonic nanostructures with arbitrary inhomogeneity and shapes are modeled by the FEM. Their complex electromagnetic interactions are accurately described by the SIE method. As a result, the near field of plasmonic nanostructures can be accurately calculated. The higher order basis functions, together with the multifrontal massively parallel sparse direct solver, are involved to provide a higher order accurate and fast solver. © 2011 IEEE.published_or_final_versio

Experimental investigations and multi-objective optimization of an air-source absorption heat pump for residential district heating

The traditional single-effect absorption heat pump is an effective district heating measure, while the low ambient temperature will degrade its performance significantly. To overcome this dilemma, a novel air-source absorption heat pump (ASAHP) for district heating (DH) is proposed in this paper. This system can operate at low ambient temperature and recover the waste heat of the flue gas with higher efficiency compared with the conventional gas-fired boilers. The falling film form is adopted in the generator and absorber, which reduces the system mass flow rate and electricity consumption. The thermodynamic performance of the system is analyzed by the lumped parameter model. An experimental rig is established to study the system performance and validate the mathematical model. Results show that the proposed system is an efficient way for DH, especially in cold regions. The heating capacity and the COP of the system are 38.32 kW and 1.39 at the evaporation temperature of −10 °C, respectively. The system can provide 36.21 kW heating capacity and 39.21 kW heating capacityfg (heating capacity of the system with flue gas recovery) with flue gas recovery to heat water from 25 °C to 39.1 °C with the COP of 1.21 and COP_{fg} (COP of the system with flue gas recovery) with flue gas recovery of 1.36. The maximum ratio of COP_{fg} ith flue gas recovery to simulation value and the maximum ratio of heating capacityfg with flue gas recovery to simulation value are 92.91% and 92.23%, respectively. Additionally, to obtain the optimal operating condition, the TOPSIS decision-making method and NSGA-II technology is adopted in multi-objective optimization

Notch Signaling Activation Promotes Seizure Activity in Temporal Lobe Epilepsy

Notch signaling in the nervous system is often regarded as a developmental pathway. However, recent studies have suggested that Notch is associated with neuronal discharges. Here, focusing on temporal lobe epilepsy, we found that Notch signaling was activated in the kainic acid (KA)-induced epilepsy model and in human epileptogenic tissues. Using an acute model of seizures, we showed that DAPT, an inhibitor of Notch, inhibited ictal activity. In contrast, pretreatment with exogenous Jagged1 to elevate Notch signaling before KA application had proconvulsant effects. In vivo, we demonstrated that the impacts of activated Notch signaling on seizures can in part be attributed to the regulatory role of Notch signaling on excitatory synaptic activity in CA1 pyramidal neurons. In vitro, we found that DAPT treatment impaired synaptic vesicle endocytosis in cultured hippocampal neurons. Taken together, our findings suggest a correlation between aberrant Notch signaling and epileptic seizures. Notch signaling is up-regulated in response to seizure activity, and its activation further promotes neuronal excitation of CA1 pyramidal neurons in acute seizures

Model development and numerical analysis of a vertical falling film absorption heat pump

Traditional gas fired boilers and air-source heat pumps are not efficient for heating when the outdoor temperature is low, while the air-source heat pump is still one of the most promoting measures for building energy-efficient heating. In this study, a novel air-source gas-fired absorption heat pump with vertical falling film exchangers has been proposed for district heating. Compared with conventional gas fired boilers, the proposed system has higher efficiency, since it can absorb heat from the ambient air. A lumped and distributed parameter coupled numerical model is established to analyze its thermodynamic performance, together with a test rig established to validate the numerical model. Experimental results indicated that when the evaporator temperature increased from −10 °C to −5 °C, the coefficient of performance rose from 1.53 to 1.62, and heating capacity improved from 36.88 kW to 45.32 kW. Additionally, the coupled model showed high prediction accuracy, with the maximum error less than 8%. Due to the opposite contributions of the supply water temperature and water flow rate to the coefficient of performance, the genetic algorithm was adopted to identify the optimal solution of a multi-objective optimization procedure. Results displayed that the proposed system was feasible and efficient for heating in cold region under different operating conditions

Performance analysis and optimization for a novel air-source gas-fired absorption heat pump

In district heating technologies, gas fired boilers and conventional heat pumps have poor performance at low ambient temperature. To tackle this issue, this study has proposed a novel air-source gas-fired absorption heat pump for district heating with flue gas recovery. Compared with conventional absorption heat pumps, the proposed solution in this study can absorb heat from both air and flue gas. Additionally, the working fluid works properly when air temperature is below 0 °C, safe and nonflammable. To analyze the economic and the thermodynamic performance of this air-source gas-fired absorption heat pump, a mathematical model, considering energy, exergy, economy and environment, has been developed. According to the simulation results of the model, the proposed air-source gas-fired absorption heat pump system here had good stability and feasibility under various operational conditions. However, as the payback period and the exergy destruction were found to be conflicting with each other, a multi-objective optimization method was established to minimize the system’s payback period and exergy destruction simultaneously. Additionally, the technique for order preference by similarity to an ideal solution decision-making method has been applied to look for the optimal solutions in the Pareto frontier, with optimal solutions of the system under different operational conditions recommended