656 research outputs found
PROPERTIES AND STRUCTURES OF Li-N BASED HYDROGEN STORAGE MATERIALS
Traditional transportation fuel, petroleum, is limited and nonrenewable, and it also causes pollutions. Hydrogen is considered one of the best alternative fuels for transportation. The key issue for using hydrogen as fuel for transportation is hydrogen storage. Lithium nitride (Li3N) is an important material which can be used for hydrogen storage. The decompositions of lithium amide (LiNH2) and lithium imide (Li2NH) are important steps for hydrogen storage in Li3N. The effect of anions (e.g. Cl-) on the decomposition of LiNH2 has never been studied. Li3N can react with LiBr to form lithium nitride bromide Li13N4Br which has been proposed as solid electrolyte for batteries.
The decompositions of LiNH2 and Li2NH with and without promoter were investigated by using temperature programmed decomposition (TPD) and X-ray diffraction (XRD) techniques. It was found that the decomposition of LiNH2 produced Li2NH and NH3 via two steps: LiNH2 into a stable intermediate species (Li1.5NH1.5) and then into Li2NH. The decomposition of Li2NH produced Li, N2 and H2 via two steps: Li2NH into an intermediate species --- Li4NH and then into Li. The kinetic analysis of Li2NH decomposition showed that the activation energies are 533.6 kJ/mol for the first step and 754.2 kJ/mol for the second step. Furthermore, XRD demonstrated that the Li4NH, which was generated in the decomposition of Li2NH, formed a solid solution with Li2NH. In the solid solution, Li4NH possesses a similar cubic structure as Li2NH. The lattice parameter of the cubic Li4NH is 0.5033nm.
The decompositions of LiNH2 and Li2NH can be promoted by chloride ion (Cl-). The introduction of Cl- into LiNH2 resulted in the generation of a new NH3 peak at low temperature of 250 °C besides the original NH3 peak at 330 °C in TPD profiles. Furthermore, Cl- can decrease the decomposition temperature of Li2NH by about 110 °C.
The degradation of Li3N was systematically investigated with techniques of XRD, Fourier transform infrared (FT-IR) spectroscopy, and UV-visible spectroscopy. It was found that O2 could not affect Li3N at room temperature. However, H2O in air can cause the degradation of Li3N due to the reaction between H2O and Li3N to LiOH. The produced LiOH can further react with CO2 in air to Li2CO3 at room temperature. Furthermore, it was revealed that Alfa-Li3N is more stable in air than Beta-Li3N.
The chemical stability of Li13N4Br in air has been investigated by XRD, TPD-MS, and UV-vis absorption as a function of time. The aging process finally leads to the degradation of the Li13N4Br into Li2CO3, lithium bromite (LiBrO2) and the release of gaseous NH3. The reaction order n = 2.43 is the best fitting for the Li13N4Br degradation in air reaction. Li13N4Br energy gap was calculated to be 2.61 eV
Spontaneous fission half-lives of heavy and superheavy nuclei within a generalized liquid drop model
We systematically calculate the spontaneous fission half-lives for heavy and
superheavy nuclei between U and Fl isotopes. The spontaneous fission process is
studied within the semi-empirical WKB approximation. The potential barrier is
obtained using a generalized liquid drop model, taking into account the nuclear
proximity, the mass asymmetry, the phenomenological pairing correction, and the
microscopic shell correction. Macroscopic inertial-mass function has been
employed for the calculation of the fission half-life. The results reproduce
rather well the experimental data. Relatively long half-lives are predicted for
many unknown nuclei, sufficient to detect them if synthesized in a laboratory.Comment: 20 pages, 5 figures, 2 tables, accepted version by Nucl. Phys.
Distributed pressure matching strategy using diffusion adaptation
Personal sound zone (PSZ) systems, which aim to create listening (bright) and
silent (dark) zones in neighboring regions of space, are often based on
time-varying acoustics. Conventional adaptive-based methods for handling PSZ
tasks suffer from the collection and processing of acoustic transfer
functions~(ATFs) between all the matching microphones and all the loudspeakers
in a centralized manner, resulting in high calculation complexity and costly
accuracy requirements. This paper presents a distributed pressure-matching (PM)
method relying on diffusion adaptation (DPM-D) to spread the computational load
amongst nodes in order to overcome these issues. The global PM problem is
defined as a sum of local costs, and the diffusion adaption approach is then
used to create a distributed solution that just needs local information
exchanges. Simulations over multi-frequency bins and a computational complexity
analysis are conducted to evaluate the properties of the algorithm and to
compare it with centralized counterparts
Enabling Deep Learning-based Physical-layer Secret Key Generation for FDD-OFDM Systems in Multi-Environments
Deep learning-based physical-layer secret key generation (PKG) has been used
to overcome the imperfect uplink/downlink channel reciprocity in frequency
division duplexing (FDD) orthogonal frequency division multiplexing (OFDM)
systems. However, existing efforts have focused on key generation for users in
a specific environment where the training samples and test samples obey the
same distribution, which is unrealistic for real world applications. This paper
formulates the PKG problem in multiple environments as a learning-based problem
by learning the knowledge such as data and models from known environments to
generate keys quickly and efficiently in multiple new environments.
Specifically, we propose deep transfer learning (DTL) and meta-learning-based
channel feature mapping algorithms for key generation. The two algorithms use
different training methods to pre-train the model in the known environments,
and then quickly adapt and deploy the model to new environments. Simulation
results show that compared with the methods without adaptation, the DTL and
meta-learning algorithms both can improve the performance of generated keys. In
addition, the complexity analysis shows that the meta-learning algorithm can
achieve better performance than the DTL algorithm with less time, lower CPU and
GPU resources
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