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The internet of things accelerates the wireless connections of massive devices to provide all kinds of new services, and thus intensifies the spectrum scarcity and access delay. Cognitive radio (CR) technology brings a solution for the issue. As a typical CR scheme, opportunistic spectrum access (OSA) has been addressed widely in the past decade. However, the tradeoff between two key indexes, the throughput of cognitive radio network (CRN) and the delay of secondary user (SU), is rarely mentioned so far, which ignites the authors' work in this paper. Taking into account a channel handoff (CH) based multi‐channel OSA scenario, the authors first analyze the opportunistic transmission performance of SU, and model the throughput of CRN as well as the handoff delay of SU. Then, the authors build up a delay‐constraint throughput optimization problem, and thus formulate the throughput‐delay tradeoff for OSA. Finally, the optimal traffic rates of SU for a good throughput‐delay tradeoff are derived according to maximizing the throughput of CRN. Theoretical and simulated results show that to enhance the throughput and to reduce the delay do not conflict always. By well adjusting the traffic rates of SU according to the traffic rates of primary user, the throughput of CRN can be improved while the handoff delay can be kept under a given level. [ABSTRACT FROM AUTHOR]

Several commonly used detection methods in the pry-Olympics study of energetic materialism with their advantages and disadvantages were bile-fly introduced. The "soft" ionization characteristics of routinizations mass spec--Tome-qty (PI MS) and As advantages in the analysis of pry-colitis produces were described. "Soft" ionization can make the hp-duces ionize without genera-ion of ionization fragments, which is convenient of- the sapid analysis of complex systems. It is conducive to online detection of the rapidly evolving inter-mediates generated from the pry-Olympics hp-chess of energetic materialism. Recent application hp-ogress of PI MS in study of pyrolysis of energetic materialism, such as NOT, FOX-7, FOX-12 and JCL-20, we-e summarized emphatically. The PI MS methods used in these studies include Jingle photon ionization mass spec--Tome-qty and atmospheric pressure pontoon-anion high -resolution mass spec--Tome-qty based on vacuum UI-ravioli (VU) bight generated from disc ha-GE lamp O- synch-O---on -radiation sources. The new pry-colitis hp-duchies and inter-mediates detected by online PI MS were ISO summarized. Finally, he future-e opportunities of PI MS in study of gene-genic materialism we-e hp-inspected. Of- characterization of fast -reactions, by Hopi-mazing he mass spec--mete- and developing high-lightness routinizations sources, it is expected to achieve Jaime-resolved measurement at millisecond O- sub-millisecond. It will help to study the pry-colitis and combustion hp-chess of gene-genic materialism undue- high temperature and high hp-assure. Of- quantitative/e measurement, it is necessary to establish and imp-rove he pontoon-action ac-doss section database of energetic materialism and main hp-duchies. 61 Refed-fences were attached. [ABSTRACT FROM AUTHOR]

Owing to the sapid release of multi-component gas during the reaction process of energetic materials, the technical issues in sampling and transmission, spectral analysis, and quantitative analysis are elaborated by using the continuous real-time and full-component scanning detection method of mass spectrometry. The technical difficulties of the reliability and distortion mechanism of different mass spectrometry sampling interfaces, the overlap of spectra due to the synchronous coupling of react-facing process and ionization, and quantitative analysis of multi-component gas are analyzed. Three representative reaction processes are defected to illustrate the secondary reaction of crystallization of the evolved gas from bolder lags, nonlinear anal-sass of he mass spectrum signal in Casa gratification, and quantitative analysis of the mass spectra of the evoked gas from the typical energetic material FAX. The re suits show hat the quantitative mass spectrometry method, equivalent characteristic spec-rum analysis (MESA®), can be used to determine the sampling distortion and accurately analyze the mass change abate of multi-component gas. Based on the continuous dynamic information for he mass changes of the multi-component gas and the mass balance of materials, components, and elements, the MESA® method nab!els accurate identification of multiple reaction processes. [ABSTRACT FROM AUTHOR]

To explore the difference in thermal stability of different CL-20 polymorphs, the initial thermal decomposition of four CL-20 polymorphs (α -, β-, γ-, and ε-) were depicted using longtime ReaxFF MD simulations at relative low temperatures of 600-900 K, which are close to the conventional thermal analysis experiments. The dynamic responses of varied CL-20 polymorphs under heating were characterized by the initial conformer transformation and thermal decomposition kinetics. The results show that under relative mild thermal stimulation conditions, conformer conversion dominates the initial responses of four CL-20 polymorphs. The molecular conformer stability of varied CL-20 polymorphs ranks as γ>β≈α>ε. Under heating conditions, ε -CL-20 converts to γ" or ϛ conformes, and γ-CL-20 converts to ϛ conformer. The above conformational transition phenomenons agree broadly with experimental phase diagram of Russell et al. Conformer conversion from ε to γ occurring very early in ε-CL-20 polymorph induces its fast initiation of decomposition reactions. In contrast, γ-CL-20 is rather stable and is conformer transformation and decomposion lags behind ε-CL-20. Once the decomposition initiates, the overall decomposition rate of γ-CL-20 polymorph is higher than that of ε-CL-20 polymorphs with increasing of thermolysis duration or tempeaatures. In terms of the reaction kinetics of weight loss and major bond cleavage during the entire thermolysis process, the thermal stability of ε-CL-20 polymorph is higher than that of γ-CL-20, which agrees with Nedelko's TG experiments. This work suggests that ReaxFF MD stimulations may be served as a computational prediction method for temperature phase diagram of polymorph conversion of energetic materials. [ABSTRACT FROM AUTHOR]

Ni(NH3)4(AFT)2 [NiC6H16N18O2, AFT = 4-amino-3-(5-tetrazolate)furazan] is synthesized and characterized by elemental analysis and Fourier-transform infrared spectroscopy for the first time. X-ray diffraction measurements are used to determine the crystal structure of compound 1. The results demonstrate that compound 1 crystallized in the orthorhombic crystal system. The nickel(II) ion is six-coordinated by N atoms from two AFT-ligands and four NH3 molecules. Its thermal properties are investigated by differential scanning calorimetry and thermogravimetry-derivative thermogravimetry methods, with the results demonstrating that the differential scanning calorimetry curve exhibits two endothermic and one exothermic processes. The endothermic processes are in the range of 130–510 °C with a peak temperature of 188 °C. The temperature from 230 to 400 °C is the exothermic process in which the peak temperature is 314.58 °C. In addition, Kissinger's and Ozawa-Doyle's methods are used for calculating the non-isothermal kinetics parameters. Moreover, the apparent activation energy (E), safety, and thermal stability parameters (T SADT, T TIT, T b) for Ni(NH3)4(AFT)2 are calculated. In addition, the calculated thermodynamic functions (∆S ≠, ∆H ≠, and ∆G ≠) for the exothermic decomposition process of Ni(NH3)4(AFT)2 are 55.07 J mol−1 K−1, 196.18 kJ mol−1, and 164.90 kJ mol−1, respectively. [ABSTRACT FROM AUTHOR]

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