Two lignite samples, Beulah No. 3 and Big Brown No. 1, were liquefied at 420 °C using H2 and synthesis gas to determine the optimum beneficial amount of H2S in the batch autoclave reactor. Under the conditions employed, 50–100 psi partial pressure of H2S, nominally 4–10 wt% of daf lignite, was optimum for both samples. Synthesis gas outperformed H2 with and without H2S for the liquefaction of the two coals. 相似文献
Layered transition metal (TM) oxides of the stoichiometry NaxMO2 (M = TM) have shown great promise in sodium‐ion batteries (SIBs); however, they are extremely sensitive to moisture. To date, most reported titanium‐based layered anodes exhibit a P2‐type structure. In contrast, O3‐type compounds are rarely investigated and their synthesis is challenging due to their higher percentage of unstable Ti3+ than the P2 type. Here, a pure phase and highly crystalline O3‐type Na0.73Li0.36Ti0.73O2 with high performance is successfully proposed in SIBs. This material delivers a reversible capacity of 108 mAh g?1 with a stable and safe potential of 0.75 V versus Na/Na+. In situ X‐ray diffraction reveals that this material does not undergo any phase transitions and exhibits a near‐zero volume change upon Na+ insertion/de‐insertion, which ensures exceptional long cycle life over 6000 cycles. Importantly, it is found that this O3‐Na0.73Li0.36Ti0.73O2 shows superior moisture stability, even when immersed into water, which are both elusive for conventional layered TM oxides in SIBs. It is believed that the small interlayer distance and high occupation of interlayer vacancy promise such unprecedented water stability. 相似文献
To effectively estimate the parameters of the multiple frequency-hopping signals, a blind parameter estimation method based on time–frequency diagram modification is proposed. Firstly, the observed signal is transformed to the time–frequency domain, using short time Fourier transform with overlapping windows. Then an energy detection method based on adaptive threshold is used to modify the time–frequency diagram, and the parameters of the frequency-hopping signals are finally obtained from the modified spectrogram. Theoretical analysis and simulation results show that the method proposed can get a clear time–frequency diagram at low signal-to-noise ratio (SNR), and its accuracy of parameter estimated is higher than that of previous methods. When SNR is ?10 dB, estimation errors of frequency, hopping time and hop duration is 0.0002, 0.0008 and 0.0013, respectively, which are about 1–2 orders of magnitude lower over the previous method.
We studied the problem of QoS guarantee for differentiated services. A two-level hierarchical scheduling framework was deployed to separate QoS metrics. Due to its desirable property of minimizing the maximum packet lateness, the Earliest Deadline First (EDF) scheduling was adopted to provide the in-class scheduling for the time-sensitive traffic. We employed an EDF scheduler combined with an active buffer management scheme (CHOKe) to improve the fairness of resource allocation and to maintain a good delay performance for real-time applications. Simulation results showed that the proposed scheme can achieve a better delay performance and make a more fair bandwidth allocation between the real-time TCP and UDP connections than the First Come First Served (FCFS) scheduling with the drop-tail buffer management which is commonly deployed in traditional IP routers. 相似文献
Lithium (Li) metal anodes have been proposed as a promising candidate for high-energy-density electrode materials in secondary batteries. However, the dendrite growth and unstable electrode–electrolyte interfaces during Li plating/stripping are fatal to their practical applications. Herein, the construction of 3D porous Au/Cu nanoscaffold prepared via a convenient template-sacrificed hot fusion construction method and a nanoseed modification process as an effective Li metal hosting material are proposed. The Au/Cu nanoscaffold can spatially guide uniform deposition of Li metal free from the growth of Li dendrites due to the homogenous Li+ ion flux and negligible nucleation overpotential. Moreover, the Cu skeleton can relieve volume change and stabilize local current density during cycling processes. Benefiting from these advantages, the symmetric cells based on self-supported Li-filled Au/Cu (Li-Au/Cu) nanoscaffold electrodes present highly stable Li plating/stripping for more than 1000 h with a low voltage hysteresis less than 90 mV and a long lifespan over 1300 h at 1.0 mA cm–2 in carbonate-based electrolytes. Impressively, the Li-Au/Cu nanoscaffold||LiFePO4 full cells also exhibit exceptional cycling stability and rate performance. This work provides a promising strategy to construct dendrite-free lithium metal anodes toward high-performance lithium metal batteries. 相似文献